First pass at implementation.

README.md

@@ -1,41 +1,110 @@
-# DGI Fixity
+# Fixity
 
 ## Introduction
 
-A module to perform fixity checks on original media.
+Perform periodic fixity checks on selected files.
+
+This module defines a new content entity type `fixity_check`. This entity is
+used as an audit trail for fixity checks performed on a related `file` entity.
+Wherein the revisions of the `fixity_check` record the results of previous 
+checks against that `file` entity.
+
+This modules requires and enforces the following constraints on `fixity_check` 
+entities:
+
+- **Must** be related to a `file`
+- `file` relations **must** be unique
+- `file` relation **cannot** be changed after creation
+- `performed` and `state` properties **cannot** be modified after creation.
+
+Users with the permission `Administer Fixity Checks` can:
+
+- Manually perform checks
+- Manually remove `fixity_check` entities and their revisions
+- Manually mark files as requiring periodic checks
+- Generate `fixity_check` entities for all previously existing files
+
+Users with the permission `View Fixity Checks` can:
+
+- View fixity audit log of Media entities
+
+A `cron` hook is setup to automatically mark files as _requiring_ periodic
+checks. As well as performing those checks on a regular basis. Email 
+notifications can be configured to alert the selected user of the status
+of all performed checks on a regular basis or only when an error occurs.
 
 ## Requirements
 
 This module requires the following modules/libraries:
 
-* [filehash](https://www.drupal.org/project/filehash)
+* [filehash]
+
+## Configuration
+
+The module can be configured at `admin/config/fixity`.
 
-## Usage
+## Drush
 
+A number of drush commands come bundled with this module.
+
+```bash
+$ drush dgi_fixity:clear --help
+Sets the periodic check flag to FALSE for all files.
+```
+
+```bash
+$ drush dgi_fixity:generate --help
+Creates a fixity_check entity for all previously created files.
+```
+
+```bash
+$ drush dgi_fixity:check --help
+Perform fixity checks on files.
+
+Options:
+  --fids[=FIDS] Comma separated list of file identifiers, or a path to a file containing file identifiers.
+                The file should have each fid separated by a new line. If not specified the modules settings
+                for sources is used to determine which files to check.
+  --force       Skip time elapsed threshold check when processing files.
+```
 
 ## Installation
 
-Install as usual, see
-[this](https://drupal.org/documentation/install/modules-themes/modules-8) for
-further information.
+Install as usual, see [this][install] for further information.
+
+Additionally after this module is first enabled, you will need to generate
+`fixity_check` entities for all pre-existing `file` entities. This does not
+require that the checks are performed, only that one `fixity_check` entity
+exists for every applicable `file` entity in the system.
+
+This can be done with `drush`:
+
+```bash
+drush dgi_fixity:generate
+```
+
+Or via the admin form on the page `admin/config/fixity/generate`.
 
 ## Troubleshooting/Issues
 
-Having problems or solved a problem? Contact
-[discoverygarden](http://support.discoverygarden.ca).
+Having problems or solved a problem? Contact [discoverygarden].
 
 ## Maintainers/Sponsors
 
 Current maintainers:
 
-* [discoverygarden](http://www.discoverygarden.ca)
+* [discoverygarden]
 
 ## Development
 
 If you would like to contribute to this module create an issue, pull request
-and or contact
-[discoverygarden](http://support.discoverygarden.ca).
+and or contact [discoverygarden].
 
 ## License
 
-[GPLv2](http://www.gnu.org/licenses/gpl-2.0.txt)
+[GPLv2][gplv2]
+
+[discoverygarden]: http://support.discoverygarden.ca
+[filehash]: https://www.drupal.org/project/filehash
+[gplv2]: http://www.gnu.org/licenses/gpl-2.0.txt
+[install]: https://drupal.org/documentation/install/modules-themes/modules-8

composer.json

@@ -0,0 +1,8 @@
+{
+  "name": "discoverygarden/dgi_fixity",
+  "type": "drupal-module",
+  "license": "GPL-2.0-or-later",
+  "require": {
+    "drupal/filehash": "^2.0"
+  }
+}

config/install/dgi_fixity.settings.yml

@@ -0,0 +1,7 @@
+sources:
+  'fixity_check_source:all_files': 'fixity_check_source:all_files'
+threshold: '-1 month'
+batch_size: 100
+notify_user: 1
+notify_user_threshold: '-1 week'
+notify_status: 2

config/install/views.view.fixity_check_source.yml

@@ -0,0 +1,246 @@
+langcode: en
+status: true
+dependencies:
+  enforced:
+    module:
+      - dgi_fixity
+  module:
+    - file
+id: fixity_check_source
+label: 'Fixity Check Source Default'
+module: views
+description: 'Default fixity check source, selects all permanent files.'
+tag: fixity
+base_table: file_managed
+base_field: fid
+display:
+  default:
+    display_plugin: default
+    id: default
+    display_title: Default
+    position: 0
+    display_options:
+      access:
+        type: none
+        options: {  }
+      cache:
+        type: none
+        options: {  }
+      query:
+        type: views_query
+        options:
+          disable_sql_rewrite: false
+          distinct: false
+          replica: false
+          query_comment: ''
+          query_tags: {  }
+      exposed_form:
+        type: basic
+        options:
+          submit_button: Apply
+          reset_button: false
+          reset_button_label: Reset
+          exposed_sorts_label: 'Sort by'
+          expose_sort_order: true
+          sort_asc_label: Asc
+          sort_desc_label: Desc
+      pager:
+        type: mini
+        options:
+          items_per_page: 10
+          offset: 0
+          id: 0
+          total_pages: null
+          expose:
+            items_per_page: false
+            items_per_page_label: 'Items per page'
+            items_per_page_options: '5, 10, 25, 50'
+            items_per_page_options_all: false
+            items_per_page_options_all_label: '- All -'
+            offset: false
+            offset_label: Offset
+          tags:
+            previous: ‹‹
+            next: ››
+      style:
+        type: default
+        options:
+          grouping: {  }
+          row_class: ''
+          default_row_class: true
+          uses_fields: false
+      row:
+        type: fields
+        options:
+          inline: {  }
+          separator: ''
+          hide_empty: false
+          default_field_elements: true
+      fields:
+        fid:
+          id: fid
+          table: file_managed
+          field: fid
+          relationship: none
+          group_type: group
+          admin_label: 'File ID'
+          label: ''
+          exclude: false
+          alter:
+            alter_text: false
+            text: ''
+            make_link: false
+            path: ''
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: ''
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: true
+            ellipsis: true
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: false
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: false
+          empty: ''
+          hide_empty: true
+          empty_zero: false
+          hide_alter_empty: true
+          click_sort_column: value
+          type: number_unformatted
+          settings: {  }
+          group_column: value
+          group_columns: {  }
+          group_rows: true
+          delta_limit: 0
+          delta_offset: 0
+          delta_reversed: false
+          delta_first_last: false
+          multi_type: separator
+          separator: ', '
+          field_api_classes: false
+          entity_type: file
+          entity_field: fid
+          plugin_id: field
+      filters:
+        status:
+          id: status
+          table: file_managed
+          field: status
+          relationship: none
+          group_type: group
+          admin_label: ''
+          operator: in
+          value:
+            1: '1'
+          group: 1
+          exposed: false
+          expose:
+            operator_id: ''
+            label: ''
+            description: ''
+            use_operator: false
+            operator: ''
+            operator_limit_selection: false
+            operator_list: {  }
+            identifier: ''
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+            reduce: false
+          is_grouped: false
+          group_info:
+            label: ''
+            description: ''
+            identifier: ''
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items: {  }
+          entity_type: file
+          entity_field: status
+          plugin_id: file_status
+      sorts:
+        fid:
+          id: fid
+          table: file_managed
+          field: fid
+          relationship: none
+          group_type: group
+          admin_label: 'File ID'
+          order: ASC
+          exposed: false
+          expose:
+            label: ''
+          entity_type: file
+          entity_field: fid
+          plugin_id: standard
+      header: {  }
+      footer: {  }
+      empty: {  }
+      relationships: {  }
+      arguments: {  }
+      display_extenders: {  }
+      show_admin_links: false
+    cache_metadata:
+      max-age: -1
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+        - url.query_args
+      tags: {  }
+  all_files:
+    display_plugin: entity_reference
+    id: all_files
+    display_title: 'All Files'
+    position: 1
+    display_options:
+      display_extenders: {  }
+      style:
+        type: entity_reference
+        options:
+          search_fields:
+            fid: fid
+      row:
+        type: entity_reference
+        options:
+          default_field_elements: false
+          inline: {  }
+          separator: '-'
+          hide_empty: true
+      display_description: 'Gets all files regardless of state or usage'
+      pager:
+        type: some
+        options:
+          items_per_page: 10
+          offset: 0
+    cache_metadata:
+      max-age: -1
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+      tags: {  }

config/install/views.view.fixity_check_status.yml

@@ -0,0 +1,824 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - dgi_fixity
+    - file
+    - user
+id: fixity_check_status
+label: 'Fixity Check Status'
+module: views
+description: 'Find and manage fixity checks'
+tag: fixity
+base_table: fixity_check
+base_field: id
+display:
+  default:
+    display_plugin: default
+    id: default
+    display_title: Default
+    position: 0
+    display_options:
+      access:
+        type: perm
+        options:
+          perm: 'administer fixity checks'
+      cache:
+        type: tag
+        options: {  }
+      query:
+        type: views_query
+        options:
+          disable_sql_rewrite: false
+          distinct: false
+          replica: false
+          query_comment: ''
+          query_tags: {  }
+      exposed_form:
+        type: basic
+        options:
+          submit_button: Filter
+          reset_button: false
+          reset_button_label: Reset
+          exposed_sorts_label: 'Sort by'
+          expose_sort_order: true
+          sort_asc_label: Asc
+          sort_desc_label: Desc
+      pager:
+        type: mini
+        options:
+          items_per_page: 10
+          offset: 0
+          id: 0
+          total_pages: null
+          expose:
+            items_per_page: false
+            items_per_page_label: 'Items per page'
+            items_per_page_options: '5, 10, 25, 50'
+            items_per_page_options_all: false
+            items_per_page_options_all_label: '- All -'
+            offset: false
+            offset_label: Offset
+          tags:
+            previous: ‹‹
+            next: ››
+      style:
+        type: table
+        options:
+          grouping: {  }
+          row_class: ''
+          default_row_class: true
+          override: true
+          sticky: false
+          caption: ''
+          summary: ''
+          description: ''
+          columns:
+            file: file
+            state: state
+            performed: performed
+            operations: operations
+          info:
+            file:
+              sortable: false
+              default_sort_order: asc
+              align: ''
+              separator: ''
+              empty_column: false
+              responsive: ''
+            state:
+              sortable: true
+              default_sort_order: asc
+              align: ''
+              separator: ''
+              empty_column: false
+              responsive: ''
+            performed:
+              sortable: true
+              default_sort_order: desc
+              align: ''
+              separator: ''
+              empty_column: false
+              responsive: ''
+            operations:
+              align: ''
+              separator: ''
+              empty_column: false
+              responsive: ''
+          default: performed
+          empty_table: false
+      row:
+        type: fields
+      fields:
+        fixity_check_bulk_form:
+          id: fixity_check_bulk_form
+          table: fixity_check
+          field: fixity_check_bulk_form
+          relationship: none
+          group_type: group
+          admin_label: ''
+          label: ''
+          exclude: false
+          alter:
+            alter_text: false
+            text: ''
+            make_link: false
+            path: ''
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: ''
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: true
+            ellipsis: true
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: false
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_empty: false
+          empty_zero: false
+          hide_alter_empty: true
+          action_title: Action
+          include_exclude: exclude
+          selected_actions: {  }
+          entity_type: fixity_check
+          plugin_id: bulk_form
+        view_fixity_check:
+          id: view_fixity_check
+          table: fixity_check
+          field: view_fixity_check
+          relationship: none
+          group_type: group
+          admin_label: ''
+          label: ''
+          exclude: true
+          alter:
+            alter_text: false
+            text: '<a href="{{ view_fixity_check }}>{{ file }}</a>'
+            make_link: false
+            path: ''
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: '{{ file }}'
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: true
+            ellipsis: true
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: false
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_empty: false
+          empty_zero: false
+          hide_alter_empty: true
+          text: ''
+          output_url_as_text: true
+          absolute: false
+          entity_type: fixity_check
+          plugin_id: entity_link
+        file_1:
+          id: file_1
+          table: fixity_check
+          field: file
+          relationship: none
+          group_type: group
+          admin_label: ''
+          label: Check
+          exclude: false
+          alter:
+            alter_text: false
+            text: '<a href="{{ view_fixity_check }}">{{ file_1 }}</a>'
+            make_link: true
+            path: '{{ view_fixity_check }}'
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: ''
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: true
+            ellipsis: true
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: false
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_empty: false
+          empty_zero: false
+          hide_alter_empty: true
+          click_sort_column: target_id
+          type: entity_reference_label
+          settings:
+            link: false
+          group_column: target_id
+          group_columns: {  }
+          group_rows: true
+          delta_limit: 0
+          delta_offset: 0
+          delta_reversed: false
+          delta_first_last: false
+          multi_type: separator
+          separator: ', '
+          field_api_classes: false
+          entity_type: fixity_check
+          entity_field: file
+          plugin_id: field
+        state:
+          id: state
+          table: fixity_check
+          field: state
+          relationship: none
+          group_type: group
+          admin_label: ''
+          label: State
+          exclude: false
+          alter:
+            alter_text: false
+            text: ''
+            make_link: false
+            path: ''
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: ''
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: true
+            ellipsis: true
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: false
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_empty: false
+          empty_zero: false
+          hide_alter_empty: true
+          click_sort_column: value
+          type: dgi_fixity_state
+          settings: {  }
+          group_column: value
+          group_columns: {  }
+          group_rows: true
+          delta_limit: 0
+          delta_offset: 0
+          delta_reversed: false
+          delta_first_last: false
+          multi_type: separator
+          separator: ', '
+          field_api_classes: false
+          entity_type: fixity_check
+          entity_field: state
+          plugin_id: field
+        performed:
+          id: performed
+          table: fixity_check
+          field: performed
+          relationship: none
+          group_type: group
+          admin_label: ''
+          label: Performed
+          exclude: false
+          alter:
+            alter_text: false
+            text: ''
+            make_link: false
+            path: ''
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: ''
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: true
+            ellipsis: true
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: false
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_empty: false
+          empty_zero: false
+          hide_alter_empty: true
+          click_sort_column: value
+          type: timestamp_ago
+          settings:
+            future_format: '@interval hence'
+            past_format: '@interval ago'
+            granularity: 2
+          group_column: value
+          group_columns: {  }
+          group_rows: true
+          delta_limit: 0
+          delta_offset: 0
+          delta_reversed: false
+          delta_first_last: false
+          multi_type: separator
+          separator: ', '
+          field_api_classes: false
+          entity_type: fixity_check
+          entity_field: performed
+          plugin_id: field
+        periodic:
+          id: periodic
+          table: fixity_check
+          field: periodic
+          relationship: none
+          group_type: group
+          admin_label: ''
+          label: Periodic
+          exclude: false
+          alter:
+            alter_text: false
+            text: ''
+            make_link: false
+            path: ''
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: ''
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: true
+            ellipsis: true
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: false
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_empty: false
+          empty_zero: false
+          hide_alter_empty: true
+          click_sort_column: value
+          type: boolean
+          settings:
+            format: default
+            format_custom_true: ''
+            format_custom_false: ''
+          group_column: value
+          group_columns: {  }
+          group_rows: true
+          delta_limit: 0
+          delta_offset: 0
+          delta_reversed: false
+          delta_first_last: false
+          multi_type: separator
+          separator: ', '
+          field_api_classes: false
+          entity_type: fixity_check
+          entity_field: periodic
+          plugin_id: field
+        operations:
+          table: fixity_check
+          field: operations
+          id: operations
+          entity_type: null
+          entity_field: null
+          plugin_id: entity_operations
+          relationship: none
+          group_type: group
+          admin_label: ''
+          label: 'Operations links'
+          exclude: false
+          alter:
+            alter_text: false
+            text: ''
+            make_link: false
+            path: ''
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: ''
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: true
+            ellipsis: true
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: true
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_empty: false
+          empty_zero: false
+          hide_alter_empty: true
+          destination: false
+      filters:
+        filename:
+          id: filename
+          table: file_managed
+          field: filename
+          relationship: file
+          group_type: group
+          admin_label: ''
+          operator: contains
+          value: ''
+          group: 1
+          exposed: true
+          expose:
+            operator_id: filename_op
+            label: Filename
+            description: ''
+            use_operator: false
+            operator: filename_op
+            operator_limit_selection: false
+            operator_list: {  }
+            identifier: filename
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+              anonymous: '0'
+              administrator: '0'
+            placeholder: ''
+          is_grouped: false
+          group_info:
+            label: ''
+            description: ''
+            identifier: ''
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items: {  }
+          entity_type: file
+          entity_field: filename
+          plugin_id: string
+        state:
+          id: state
+          table: fixity_check
+          field: state
+          relationship: none
+          group_type: group
+          admin_label: ''
+          operator: '='
+          value:
+            min: ''
+            max: ''
+            value: ''
+          group: 1
+          exposed: true
+          expose:
+            operator_id: state_op
+            label: State
+            description: ''
+            use_operator: false
+            operator: state_op
+            operator_limit_selection: false
+            operator_list: {  }
+            identifier: state
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+              anonymous: '0'
+              administrator: '0'
+              fedoraadmin: '0'
+            placeholder: ''
+            min_placeholder: ''
+            max_placeholder: ''
+          is_grouped: true
+          group_info:
+            label: State
+            description: ''
+            identifier: state
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items:
+              1:
+                title: Passed
+                operator: '='
+                value:
+                  value: '1'
+                  min: ''
+                  max: ''
+              2:
+                title: Failed
+                operator: '!='
+                value:
+                  value: '1'
+                  min: ''
+                  max: ''
+          entity_type: fixity_check
+          entity_field: state
+          plugin_id: numeric
+        performed:
+          id: performed
+          table: fixity_check
+          field: performed
+          relationship: none
+          group_type: group
+          admin_label: ''
+          operator: '='
+          value:
+            min: ''
+            max: ''
+            value: '1970-01-01 00:00:00'
+            type: date
+          group: 1
+          exposed: true
+          expose:
+            operator_id: performed_op
+            label: Performed
+            description: ''
+            use_operator: false
+            operator: performed_op
+            operator_limit_selection: false
+            operator_list: {  }
+            identifier: performed
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+              anonymous: '0'
+              administrator: '0'
+              fedoraadmin: '0'
+            placeholder: ''
+            min_placeholder: ''
+            max_placeholder: ''
+          is_grouped: true
+          group_info:
+            label: Performed
+            description: ''
+            identifier: performed
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items:
+              1:
+                title: 'True'
+                operator: '!='
+                value:
+                  type: date
+                  value: '1970-01-01 00:00:00'
+                  min: ''
+                  max: ''
+              2:
+                title: 'False'
+                operator: '='
+                value:
+                  type: date
+                  value: '1970-01-01 00:00:00'
+                  min: ''
+                  max: ''
+          entity_type: fixity_check
+          entity_field: performed
+          plugin_id: date
+        periodic:
+          id: periodic
+          table: fixity_check
+          field: periodic
+          relationship: none
+          group_type: group
+          admin_label: ''
+          operator: '='
+          value: All
+          group: 1
+          exposed: true
+          expose:
+            operator_id: ''
+            label: Periodic
+            description: ''
+            use_operator: false
+            operator: periodic_op
+            operator_limit_selection: false
+            operator_list: {  }
+            identifier: periodic
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+              anonymous: '0'
+              administrator: '0'
+          is_grouped: false
+          group_info:
+            label: ''
+            description: ''
+            identifier: ''
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items: {  }
+          entity_type: fixity_check
+          entity_field: periodic
+          plugin_id: boolean
+      sorts:
+        performed:
+          id: performed
+          table: fixity_check
+          field: performed
+          relationship: none
+          group_type: group
+          admin_label: ''
+          order: DESC
+          exposed: false
+          expose:
+            label: Performed
+          granularity: second
+          entity_type: fixity_check
+          entity_field: performed
+          plugin_id: date
+      title: Status
+      header: {  }
+      footer: {  }
+      empty:
+        area_text_custom:
+          id: area_text_custom
+          table: views
+          field: area_text_custom
+          relationship: none
+          group_type: group
+          admin_label: ''
+          empty: true
+          tokenize: false
+          content: 'No fixity checks have been performed.'
+          plugin_id: text_custom
+      relationships:
+        file:
+          id: file
+          table: fixity_check
+          field: file
+          relationship: none
+          group_type: group
+          admin_label: File
+          required: false
+          entity_type: fixity_check
+          entity_field: file
+          plugin_id: standard
+      arguments: {  }
+      display_extenders: {  }
+      filter_groups:
+        operator: AND
+        groups:
+          1: AND
+    cache_metadata:
+      max-age: 0
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+        - url
+        - url.query_args
+        - user.permissions
+      tags: {  }
+  fixity_checks:
+    display_plugin: page
+    id: fixity_checks
+    display_title: Page
+    position: 1
+    display_options:
+      display_extenders: {  }
+      path: admin/reports/fixity
+      enabled: true
+    cache_metadata:
+      max-age: 0
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+        - url
+        - url.query_args
+        - user.permissions
+      tags: {  }

config/optional/system.action.fixity_check_check_action.yml

@@ -0,0 +1,10 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - dgi_fixity
+id: fixity_check_check_action
+label: 'Perform check'
+type: fixity_check
+plugin: dgi_fixity:check_action:fixity_check
+configuration: {  }

config/optional/system.action.fixity_check_delete_action.yml

@@ -0,0 +1,10 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - dgi_fixity
+id: fixity_check_delete_action
+label: 'Delete check'
+type: fixity_check
+plugin: entity:delete_action:fixity_check
+configuration: {  }

config/optional/system.action.fixity_check_periodic_disable_action.yml

@@ -0,0 +1,10 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - dgi_fixity
+id: fixity_check_periodic_disable_action
+label: 'Disable periodic checks'
+type: fixity_check
+plugin: dgi_fixity:periodic_disable_action:fixity_check
+configuration: {  }

config/optional/system.action.fixity_check_periodic_enable_action.yml

@@ -0,0 +1,10 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - dgi_fixity
+id: fixity_check_periodic_enable_action
+label: 'Enable periodic checks'
+type: fixity_check
+plugin: dgi_fixity:periodic_enable_action:fixity_check
+configuration: {  }

config/optional/system.action.media_check_action.yml

@@ -0,0 +1,11 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - media
+    - dgi_fixity
+id: media_check_action
+label: 'Check media'
+type: media
+plugin: dgi_fixity:check_action:media
+configuration: {  }

config/optional/system.action.media_periodic_disable_action.yml

@@ -0,0 +1,11 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - dgi_fixity
+    - media
+id: media_periodic_disable_action
+label: 'Disable periodic media checks'
+type: media
+plugin: dgi_fixity:periodic_disable_action:media
+configuration: {  }

config/optional/system.action.media_periodic_enable_action.yml

@@ -0,0 +1,11 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - dgi_fixity
+    - media
+id: media_periodic_enable_action
+label: 'Enable periodic media checks'
+type: media
+plugin: dgi_fixity:periodic_enable_action:media
+configuration: {  }

config/optional/views.view.fixity_check_source_islandora.yml

@@ -0,0 +1,901 @@
+langcode: en
+status: true
+dependencies:
+  enforced:
+    config:
+      # Requires the following fields to work.
+      - field.storage.media.field_media_use
+      - field.storage.taxonomy_term.field_external_uri
+    module:
+      - dgi_fixity
+  module:
+    - file
+    - media
+    - taxonomy
+id: fixity_check_source_islandora
+label: 'Fixity Check Source Islandora'
+module: views
+description: 'Fixity Check Source for islandora, selects all "Original Files"'
+tag: fixity
+base_table: file_managed
+base_field: fid
+display:
+  default:
+    display_plugin: default
+    id: default
+    display_title: Default
+    position: 0
+    display_options:
+      access:
+        type: none
+        options: {  }
+      cache:
+        type: none
+        options: {  }
+      query:
+        type: views_query
+        options:
+          disable_sql_rewrite: false
+          distinct: false
+          replica: false
+          query_comment: ''
+          query_tags: {  }
+      exposed_form:
+        type: basic
+        options:
+          submit_button: Apply
+          reset_button: false
+          reset_button_label: Reset
+          exposed_sorts_label: 'Sort by'
+          expose_sort_order: true
+          sort_asc_label: Asc
+          sort_desc_label: Desc
+      pager:
+        type: mini
+        options:
+          items_per_page: 10
+          offset: 0
+          id: 0
+          total_pages: null
+          expose:
+            items_per_page: false
+            items_per_page_label: 'Items per page'
+            items_per_page_options: '5, 10, 25, 50'
+            items_per_page_options_all: false
+            items_per_page_options_all_label: '- All -'
+            offset: false
+            offset_label: Offset
+          tags:
+            previous: ‹‹
+            next: ››
+      style:
+        type: default
+        options:
+          grouping: {  }
+          row_class: ''
+          default_row_class: true
+          uses_fields: false
+      row:
+        type: fields
+        options:
+          inline: {  }
+          separator: ''
+          hide_empty: false
+          default_field_elements: true
+      fields:
+        fid:
+          id: fid
+          table: file_managed
+          field: fid
+          relationship: none
+          group_type: group
+          admin_label: ''
+          label: ''
+          exclude: false
+          alter:
+            alter_text: false
+            text: ''
+            make_link: false
+            path: ''
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: ''
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: true
+            ellipsis: true
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: false
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_empty: false
+          empty_zero: false
+          hide_alter_empty: true
+          click_sort_column: value
+          type: number_unformatted
+          settings: {  }
+          group_column: value
+          group_columns: {  }
+          group_rows: true
+          delta_limit: 0
+          delta_offset: 0
+          delta_reversed: false
+          delta_first_last: false
+          multi_type: separator
+          separator: ', '
+          field_api_classes: false
+          entity_type: file
+          entity_field: fid
+          plugin_id: field
+      filters:
+        status:
+          id: status
+          table: file_managed
+          field: status
+          relationship: none
+          group_type: group
+          admin_label: ''
+          operator: in
+          value:
+            1: '1'
+          group: 1
+          exposed: false
+          expose:
+            operator_id: ''
+            label: ''
+            description: ''
+            use_operator: false
+            operator: ''
+            operator_limit_selection: false
+            operator_list: {  }
+            identifier: ''
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+            reduce: false
+          is_grouped: false
+          group_info:
+            label: ''
+            description: ''
+            identifier: ''
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items: {  }
+          entity_type: file
+          entity_field: status
+          plugin_id: file_status
+      sorts:
+        fid:
+          id: fid
+          table: file_managed
+          field: fid
+          relationship: none
+          group_type: group
+          admin_label: ''
+          order: ASC
+          exposed: false
+          expose:
+            label: ''
+          entity_type: file
+          entity_field: fid
+          plugin_id: standard
+      header: {  }
+      footer: {  }
+      empty: {  }
+      relationships: {  }
+      arguments: {  }
+      display_extenders: {  }
+      show_admin_links: false
+    cache_metadata:
+      max-age: -1
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+        - url.query_args
+      tags: {  }
+  original_files_audio:
+    display_plugin: entity_reference
+    id: original_files_audio
+    display_title: 'Original File: Audio'
+    position: 1
+    display_options:
+      display_extenders: {  }
+      style:
+        type: entity_reference
+        options:
+          search_fields:
+            fid: fid
+      display_description: 'Gets the "Original File" files of Audio Media'
+      row:
+        type: entity_reference
+        options:
+          default_field_elements: false
+          inline: {  }
+          separator: '-'
+          hide_empty: true
+      relationships:
+        reverse_field_media_audio_file_media:
+          id: reverse_field_media_audio_file_media
+          table: file_managed
+          field: reverse_field_media_audio_file_media
+          relationship: none
+          group_type: group
+          admin_label: Audio
+          required: true
+          entity_type: file
+          plugin_id: entity_reverse
+        field_media_use:
+          id: field_media_use
+          table: media__field_media_use
+          field: field_media_use
+          relationship: reverse_field_media_audio_file_media
+          group_type: group
+          admin_label: 'Media Use'
+          required: true
+          plugin_id: standard
+      defaults:
+        relationships: false
+        filters: false
+        filter_groups: false
+      filters:
+        status:
+          id: status
+          table: file_managed
+          field: status
+          relationship: none
+          group_type: group
+          admin_label: ''
+          operator: in
+          value:
+            1: '1'
+          group: 1
+          exposed: false
+          expose:
+            operator_id: ''
+            label: ''
+            description: ''
+            use_operator: false
+            operator: ''
+            operator_limit_selection: false
+            operator_list: {  }
+            identifier: ''
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+            reduce: false
+          is_grouped: false
+          group_info:
+            label: ''
+            description: ''
+            identifier: ''
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items: {  }
+          entity_type: file
+          entity_field: status
+          plugin_id: file_status
+        field_external_uri_uri:
+          id: field_external_uri_uri
+          table: taxonomy_term__field_external_uri
+          field: field_external_uri_uri
+          relationship: field_media_use
+          group_type: group
+          admin_label: 'Original File'
+          operator: '='
+          value: 'http://pcdm.org/use#OriginalFile'
+          group: 1
+          exposed: false
+          expose:
+            operator_id: ''
+            label: ''
+            description: ''
+            use_operator: false
+            operator: ''
+            operator_limit_selection: false
+            operator_list: {  }
+            identifier: ''
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+            placeholder: ''
+          is_grouped: false
+          group_info:
+            label: ''
+            description: ''
+            identifier: ''
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items: {  }
+          plugin_id: string
+      filter_groups:
+        operator: AND
+        groups:
+          1: AND
+    cache_metadata:
+      max-age: -1
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+      tags: {  }
+  original_files_document:
+    display_plugin: entity_reference
+    id: original_files_document
+    display_title: 'Original File: Document'
+    position: 2
+    display_options:
+      display_extenders: {  }
+      style:
+        type: entity_reference
+        options:
+          search_fields:
+            fid: fid
+      display_description: 'Gets the "Original File" files of Document Media'
+      row:
+        type: entity_reference
+        options:
+          default_field_elements: false
+          inline: {  }
+          separator: '-'
+          hide_empty: true
+      relationships:
+        reverse_field_media_document_media:
+          id: reverse_field_media_document_media
+          table: file_managed
+          field: reverse_field_media_document_media
+          relationship: none
+          group_type: group
+          admin_label: Document
+          required: true
+          entity_type: file
+          plugin_id: entity_reverse
+        field_media_use:
+          id: field_media_use
+          table: media__field_media_use
+          field: field_media_use
+          relationship: reverse_field_media_document_media
+          group_type: group
+          admin_label: 'Media Use'
+          required: true
+          plugin_id: standard
+      defaults:
+        relationships: false
+        filters: false
+        filter_groups: false
+      filters:
+        status:
+          id: status
+          table: file_managed
+          field: status
+          relationship: none
+          group_type: group
+          admin_label: ''
+          operator: in
+          value:
+            1: '1'
+          group: 1
+          exposed: false
+          expose:
+            operator_id: ''
+            label: ''
+            description: ''
+            use_operator: false
+            operator: ''
+            operator_limit_selection: false
+            operator_list: {  }
+            identifier: ''
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+            reduce: false
+          is_grouped: false
+          group_info:
+            label: ''
+            description: ''
+            identifier: ''
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items: {  }
+          entity_type: file
+          entity_field: status
+          plugin_id: file_status
+        field_external_uri_uri:
+          id: field_external_uri_uri
+          table: taxonomy_term__field_external_uri
+          field: field_external_uri_uri
+          relationship: field_media_use
+          group_type: group
+          admin_label: 'Original File'
+          operator: '='
+          value: 'http://pcdm.org/use#OriginalFile'
+          group: 1
+          exposed: false
+          expose:
+            operator_id: ''
+            label: ''
+            description: ''
+            use_operator: false
+            operator: ''
+            operator_limit_selection: false
+            operator_list: {  }
+            identifier: ''
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+            placeholder: ''
+          is_grouped: false
+          group_info:
+            label: ''
+            description: ''
+            identifier: ''
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items: {  }
+          plugin_id: string
+      filter_groups:
+        operator: AND
+        groups:
+          1: AND
+    cache_metadata:
+      max-age: -1
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+      tags: {  }
+  original_files_file:
+    display_plugin: entity_reference
+    id: original_files_file
+    display_title: 'Original File: File'
+    position: 3
+    display_options:
+      display_extenders: {  }
+      style:
+        type: entity_reference
+        options:
+          search_fields:
+            fid: fid
+      display_description: 'Gets the "Original File" files of File Media'
+      row:
+        type: entity_reference
+        options:
+          default_field_elements: false
+          inline: {  }
+          separator: '-'
+          hide_empty: true
+      relationships:
+        reverse_field_media_file_media:
+          id: reverse_field_media_file_media
+          table: file_managed
+          field: reverse_field_media_file_media
+          relationship: none
+          group_type: group
+          admin_label: File
+          required: true
+          entity_type: file
+          plugin_id: entity_reverse
+        field_media_use:
+          id: field_media_use
+          table: media__field_media_use
+          field: field_media_use
+          relationship: reverse_field_media_file_media
+          group_type: group
+          admin_label: 'Media Use'
+          required: true
+          plugin_id: standard
+      defaults:
+        relationships: false
+        filters: false
+        filter_groups: false
+      filters:
+        status:
+          id: status
+          table: file_managed
+          field: status
+          relationship: none
+          group_type: group
+          admin_label: ''
+          operator: in
+          value:
+            1: '1'
+          group: 1
+          exposed: false
+          expose:
+            operator_id: ''
+            label: ''
+            description: ''
+            use_operator: false
+            operator: ''
+            operator_limit_selection: false
+            operator_list: {  }
+            identifier: ''
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+            reduce: false
+          is_grouped: false
+          group_info:
+            label: ''
+            description: ''
+            identifier: ''
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items: {  }
+          entity_type: file
+          entity_field: status
+          plugin_id: file_status
+        field_external_uri_uri:
+          id: field_external_uri_uri
+          table: taxonomy_term__field_external_uri
+          field: field_external_uri_uri
+          relationship: field_media_use
+          group_type: group
+          admin_label: 'Original File'
+          operator: '='
+          value: 'http://pcdm.org/use#OriginalFile'
+          group: 1
+          exposed: false
+          expose:
+            operator_id: ''
+            label: ''
+            description: ''
+            use_operator: false
+            operator: ''
+            operator_limit_selection: false
+            operator_list: {  }
+            identifier: ''
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+            placeholder: ''
+          is_grouped: false
+          group_info:
+            label: ''
+            description: ''
+            identifier: ''
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items: {  }
+          plugin_id: string
+      filter_groups:
+        operator: AND
+        groups:
+          1: AND
+    cache_metadata:
+      max-age: -1
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+      tags: {  }
+  original_files_image:
+    display_plugin: entity_reference
+    id: original_files_image
+    display_title: 'Original File: Image'
+    position: 3
+    display_options:
+      display_extenders: {  }
+      style:
+        type: entity_reference
+        options:
+          search_fields:
+            fid: fid
+      display_description: 'Gets the "Original File" files of Image Media'
+      row:
+        type: entity_reference
+        options:
+          default_field_elements: false
+          inline: {  }
+          separator: '-'
+          hide_empty: true
+      relationships:
+        reverse_field_media_image_media:
+          id: reverse_field_media_image_media
+          table: file_managed
+          field: reverse_field_media_image_media
+          relationship: none
+          group_type: group
+          admin_label: Image
+          required: true
+          entity_type: file
+          plugin_id: entity_reverse
+        field_media_use:
+          id: field_media_use
+          table: media__field_media_use
+          field: field_media_use
+          relationship: reverse_field_media_image_media
+          group_type: group
+          admin_label: 'Media Use'
+          required: true
+          plugin_id: standard
+      defaults:
+        relationships: false
+        filters: false
+        filter_groups: false
+      filters:
+        status:
+          id: status
+          table: file_managed
+          field: status
+          relationship: none
+          group_type: group
+          admin_label: ''
+          operator: in
+          value:
+            1: '1'
+          group: 1
+          exposed: false
+          expose:
+            operator_id: ''
+            label: ''
+            description: ''
+            use_operator: false
+            operator: ''
+            operator_limit_selection: false
+            operator_list: {  }
+            identifier: ''
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+            reduce: false
+          is_grouped: false
+          group_info:
+            label: ''
+            description: ''
+            identifier: ''
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items: {  }
+          entity_type: file
+          entity_field: status
+          plugin_id: file_status
+        field_external_uri_uri:
+          id: field_external_uri_uri
+          table: taxonomy_term__field_external_uri
+          field: field_external_uri_uri
+          relationship: field_media_use
+          group_type: group
+          admin_label: 'Original File'
+          operator: '='
+          value: 'http://pcdm.org/use#OriginalFile'
+          group: 1
+          exposed: false
+          expose:
+            operator_id: ''
+            label: ''
+            description: ''
+            use_operator: false
+            operator: ''
+            operator_limit_selection: false
+            operator_list: {  }
+            identifier: ''
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+            placeholder: ''
+          is_grouped: false
+          group_info:
+            label: ''
+            description: ''
+            identifier: ''
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items: {  }
+          plugin_id: string
+      filter_groups:
+        operator: AND
+        groups:
+          1: AND
+    cache_metadata:
+      max-age: -1
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+      tags: {  }
+  original_files_video:
+    display_plugin: entity_reference
+    id: original_files_video
+    display_title: 'Original File: Video'
+    position: 3
+    display_options:
+      display_extenders: {  }
+      style:
+        type: entity_reference
+        options:
+          search_fields:
+            fid: fid
+      display_description: 'Gets the "Original File" files of Video Media'
+      row:
+        type: entity_reference
+        options:
+          default_field_elements: false
+          inline: {  }
+          separator: '-'
+          hide_empty: true
+      relationships:
+        reverse_field_media_video_file_media:
+          id: reverse_field_media_video_file_media
+          table: file_managed
+          field: reverse_field_media_video_file_media
+          relationship: none
+          group_type: group
+          admin_label: Video
+          required: true
+          entity_type: file
+          plugin_id: entity_reverse
+        field_media_use:
+          id: field_media_use
+          table: media__field_media_use
+          field: field_media_use
+          relationship: reverse_field_media_video_file_media
+          group_type: group
+          admin_label: 'Media Use'
+          required: true
+          plugin_id: standard
+      defaults:
+        relationships: false
+        filters: false
+        filter_groups: false
+      filters:
+        status:
+          id: status
+          table: file_managed
+          field: status
+          relationship: none
+          group_type: group
+          admin_label: ''
+          operator: in
+          value:
+            1: '1'
+          group: 1
+          exposed: false
+          expose:
+            operator_id: ''
+            label: ''
+            description: ''
+            use_operator: false
+            operator: ''
+            operator_limit_selection: false
+            operator_list: {  }
+            identifier: ''
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+            reduce: false
+          is_grouped: false
+          group_info:
+            label: ''
+            description: ''
+            identifier: ''
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items: {  }
+          entity_type: file
+          entity_field: status
+          plugin_id: file_status
+        field_external_uri_uri:
+          id: field_external_uri_uri
+          table: taxonomy_term__field_external_uri
+          field: field_external_uri_uri
+          relationship: field_media_use
+          group_type: group
+          admin_label: ''
+          operator: '='
+          value: 'http://pcdm.org/use#OriginalFile'
+          group: 1
+          exposed: false
+          expose:
+            operator_id: ''
+            label: ''
+            description: ''
+            use_operator: false
+            operator: ''
+            operator_limit_selection: false
+            operator_list: {  }
+            identifier: ''
+            required: false
+            remember: false
+            multiple: false
+            remember_roles:
+              authenticated: authenticated
+            placeholder: ''
+          is_grouped: false
+          group_info:
+            label: ''
+            description: ''
+            identifier: ''
+            optional: true
+            widget: select
+            multiple: false
+            remember: false
+            default_group: All
+            default_group_multiple: {  }
+            group_items: {  }
+          plugin_id: string
+      filter_groups:
+        operator: AND
+        groups:
+          1: AND
+    cache_metadata:
+      max-age: -1
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+      tags: {  }

config/schema/dgi_fixity.schema.yml

@@ -0,0 +1,22 @@
+dgi_fixity.settings:
+  type: config_object
+  label: 'Fixity check settings'
+  mapping:
+    sources:
+      type: sequence
+      label: 'File Selection for Fixity Checks'
+    threshold:
+      type: string
+      label: 'Time elapsed between Fixity Checks'
+    batch_size:
+      type: integer
+      label: 'How many files will be processed at once when performing a batch / cron job'
+    notify_status:
+      type: integer
+      label: 'Notification trigger on status'
+    notify_user:
+      type: integer
+      label: 'User to notify'
+    notify_user_threshold:
+      type: string
+      label: 'Time elapsed between notifications'

dgi_fixity.info.yml

@@ -0,0 +1,12 @@
+name: 'Fixity'
+description: "Performs fixity checks on files."
+type: module
+package: DGI
+core_version_requirement: ^8 || ^9
+configure: dgi_fixity.settings
+dependencies:
+  - drupal:file
+  - drupal:media
+  - drupal:user
+  - drupal:views
+  - filehash:filehash

dgi_fixity.install

@@ -0,0 +1,36 @@
+<?php
+
+/**
+ * @file
+ * Install hook implementations.
+ */
+
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Implements hook_requirements().
+ */
+function dgi_fixity_requirements($phase) {
+  $requirements = [];
+  if ($phase == 'runtime') {
+    /** @var \Drupal\dgi_fixity\FixityCheckServiceInterface $fixity */
+    $fixity = \Drupal::service('dgi_fixity.fixity_check');
+    $stats = $fixity->stats();
+    $elements = [];
+    foreach ($fixity->summary($stats) as $summary) {
+      $elements[] = [
+        '#markup' => $summary,
+        '#suffix' => '<br/>',
+      ];
+    }
+    $failed = $stats['failed'] > 0;
+    $out_to_date = $stats['periodic']['expired'] > 0;
+    $requirements['dgi_fixity'] = [
+      'title' => new TranslatableMarkup('Fixity'),
+      'value' => $failed ? new TranslatableMarkup('Error') : ($out_to_date ? new TranslatableMarkup('Out of date') : new TranslatableMarkup('Up to date')),
+      'description' => \Drupal::service('renderer')->render($elements),
+      'severity' => $failed ? REQUIREMENT_ERROR : ($out_to_date ? REQUIREMENT_WARNING : REQUIREMENT_OK),
+    ];
+  }
+  return $requirements;
+}

dgi_fixity.links.menu.yml

@@ -0,0 +1,11 @@
+dgi_fixity.settings:
+  title: 'Fixity'
+  description: 'Configure Fixity Settings.'
+  route_name: dgi_fixity.settings
+  parent: 'system.admin_config_media'
+
+dgi_fixity.report:
+  title: 'Fixity report'
+  description: 'Report of all fixity checks.'
+  route_name: entity.fixity_check.collection
+  parent: 'system.admin_reports'

dgi_fixity.links.task.yml

@@ -0,0 +1,45 @@
+dgi_fixity.entities:
+  class: \Drupal\Core\Menu\LocalTaskDefault
+  deriver: 'Drupal\dgi_fixity\Plugin\Derivative\FixityCheckLocalTasks'
+
+dgi_fixity.config:
+  route_name: dgi_fixity.settings
+  base_route: dgi_fixity.settings
+  title: Configuration
+
+dgi_fixity.batch:
+  route_name: dgi_fixity.batch
+  base_route: dgi_fixity.settings
+  title: Check
+
+dgi_fixity.generate:
+  route_name: dgi_fixity.generate
+  base_route: dgi_fixity.settings
+  title: Generate
+  
+entity.fixity_check.view:
+  route_name: entity.fixity_check.canonical
+  base_route: entity.fixity_check.canonical
+  title: View
+
+entity.fixity_check.edit:
+  route_name: entity.fixity_check.edit_form
+  base_route: entity.fixity_check.canonical
+  title: Edit
+
+entity.fixity_check.delete_form:
+  route_name: entity.fixity_check.delete_form
+  base_route: entity.fixity_check.canonical
+  weight: 10
+  title: Delete
+
+entity.fixity_check.revision:
+  route_name: entity.fixity_check.revision
+  base_route: entity.fixity_check.revision
+  title: Revision
+
+entity.fixity_check.revision.delete_form:
+  route_name: entity.fixity_check.revision_delete_confirm
+  base_route: entity.fixity_check.revision
+  weight: 10
+  title: Delete

dgi_fixity.module

@@ -0,0 +1,206 @@
+<?php
+
+/**
+ * @file
+ * General hook implementations.
+ */
+
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\Config\FileStorage;
+use Drupal\Core\Config\InstallStorage;
+use Drupal\Core\Config\StorageInterface;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Mail\MailFormatHelper;
+use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\Core\Url;
+use Drupal\dgi_fixity\EntityTypeInfo;
+use Drupal\dgi_fixity\Form\SettingsForm;
+use Drupal\user\Entity\User;
+
+/**
+ * Implements hook_modules_installed().
+ */
+function dgi_fixity_modules_installed($modules) {
+  // Install optional configuration for islandora / action.
+  if (in_array('islandora_defaults', $modules) || in_array('action', $modules)) {
+    $optional_install_path = \Drupal::moduleHandler()
+      ->getModule('dgi_fixity')
+      ->getPath() . '/' . InstallStorage::CONFIG_OPTIONAL_DIRECTORY;
+    /** @var \Drupal\Core\Config\ConfigInstallerInterface $config_installer */
+    $config_installer = \Drupal::service('config.installer');
+    $storage = new FileStorage($optional_install_path, StorageInterface::DEFAULT_COLLECTION);
+    // This will not overwrite the existing optional configuration if already
+    // installed.
+    $config_installer->installOptionalConfig($storage);
+  }
+}
+
+/**
+ * Implements hook_mail().
+ */
+function dgi_fixity_mail($key, &$message, $params) {
+  switch ($key) {
+    case 'notify':
+      $config = \Drupal::config(SettingsForm::CONFIG_NAME);
+      $last = \Drupal::state()->get(SettingsForm::STATE_LAST_NOTIFICATION);
+
+      if ($last !== NULL) {
+        // If enough time has not elapsed since the last notification do not
+        // send again.
+        $threshold = strtotime($config->get(SettingsForm::NOTIFY_USER_THRESHOLD));
+        if ($last > $threshold) {
+          $message['send'] = FALSE;
+          return;
+        }
+      }
+
+      // Check if the configuration has enabled notifications.
+      $notify_status = $config->get(SettingsForm::NOTIFY_STATUS);
+      if ($notify_status === SettingsForm::NOTIFY_STATUS_NEVER) {
+        $message['send'] = FALSE;
+        return;
+      }
+
+      /** @var \Drupal\dgi_fixity\FixityCheckServiceInterface $fixity */
+      $fixity = \Drupal::service('dgi_fixity.fixity_check');
+      $stats = $fixity->stats();
+      // Only notify if an error has occurred.
+      if ($notify_status == SettingsForm::NOTIFY_STATUS_ERROR && $stats['failed'] === FALSE) {
+        $message['send'] = FALSE;
+        return;
+      }
+
+      $now = \Drupal::time()->getRequestTime();
+      $subject = (new TranslatableMarkup('Fixity Check Report - @now', ['@now' => date(DATE_RFC7231, $now)]))->render();
+      $body = $fixity->summary($stats);
+      if ($stats['failed'] !== 0) {
+        $body[] = (new TranslatableMarkup(
+          'There are failed checks which require your attention please review the current state of checks <a href="@site">here</a>.',
+          ['@site' => Url::fromRoute('entity.fixity_check.collection', [], ['absolute' => TRUE])->toString()]
+        ))->render();
+      }
+
+      $message['subject'] = $subject;
+      foreach ($body as $line) {
+        $message['body'][] = MailFormatHelper::htmlToText($line);
+      }
+
+      // Track when the last message was sent.
+      \Drupal::state()->set(SettingsForm::STATE_LAST_NOTIFICATION, $now);
+      break;
+  }
+}
+
+/**
+ * Implements hook_cron().
+ */
+function dgi_fixity_cron() {
+  $queued = \Drupal::time()->getRequestTime();
+  $settings = \Drupal::config(SettingsForm::CONFIG_NAME);
+  $threshold = strtotime($settings->get(SettingsForm::THRESHOLD));
+  $sources = $settings->get(SettingsForm::SOURCES);
+
+  // Update enabled periodic checks.
+  $queue = \Drupal::queue('dgi_fixity.process_source');
+  foreach ($sources as $source) {
+    // It safe to have queue processing a source multiple times,
+    // they will steal work from each other but will not conflict.
+    $queue->createItem($source);
+  }
+
+  /** @var \Drupal\dgi_fixity\FixityCheckStorageInterface $storage */
+  $storage = \Drupal::entityTypeManager()->getStorage('fixity_check');
+
+  // Queue items that exceed the current threshold.
+  $storage->queue($queued, $threshold, 100);
+
+  // Dequeued items after 6 hours assuming the check has failed.
+  // They will be re-queued if appropriate on the next cron run.
+  $storage->dequeue($queued - (3600 * 6));
+
+  // Send notification if appropriate.
+  $uid = $settings->get(SettingsForm::NOTIFY_USER);
+  $user = User::load($uid);
+  if ($user) {
+    \Drupal::service('plugin.manager.mail')->mail('dgi_fixity', 'notify', $user->getEmail(), $user->getPreferredAdminLangcode(TRUE));
+  }
+}
+
+/**
+ * Implements hook_entity_type_alter().
+ */
+function dgi_fixity_entity_type_alter(array &$entity_types) {
+  return \Drupal::service('class_resolver')
+    ->getInstanceFromDefinition(EntityTypeInfo::class)
+    ->entityTypeAlter($entity_types);
+}
+
+/**
+ * Implements hook_entity_operation().
+ */
+function dgi_fixity_entity_operation(EntityInterface $entity) {
+  return \Drupal::service('class_resolver')
+    ->getInstanceFromDefinition(EntityTypeInfo::class)
+    ->entityOperation($entity);
+}
+
+/**
+ * Implements hook_ENTITY_TYPE_insert().
+ */
+function dgi_fixity_file_insert(EntityInterface $entity) {
+  // Make sure the fixity_check table contains a row for every file.
+  \Drupal::entityTypeManager()
+    ->getStorage('fixity_check')
+    ->create([
+      'file' => $entity->id(),
+    ])
+    ->save();
+}
+
+/**
+ * Implements hook_ENTITY_TYPE_delete().
+ */
+function dgi_fixity_file_delete(EntityInterface $entity) {
+  /** @var \Drupal\dgi_fixity\FixityCheckStorageInterface $storage */
+  $storage = \Drupal::entityTypeManager()->getStorage('fixity_check');
+  $checks = $storage->loadByProperties([
+    'file' => $entity->id(),
+  ]);
+  // Remove checks for non-existent files.
+  $storage->delete($checks);
+}
+
+/**
+ * Implements hook_ENTITY_TYPE_revision_create().
+ */
+function dgi_fixity_fixity_check_revision_create(EntityInterface $entity) {
+  Cache::invalidateTags([
+    'fixity_check:' . $entity->id() . ':revisions_list',
+  ]);
+}
+
+/**
+ * Implements hook_ENTITY_TYPE_revision_delete().
+ */
+function dgi_fixity_fixity_check_revision_delete(EntityInterface $entity) {
+  Cache::invalidateTags([
+    'fixity_check:' . $entity->id() . ':revisions_list',
+  ]);
+}
+
+/**
+ * Implements hook_help().
+ */
+function dgi_fixity_help($route_name, RouteMatchInterface $route_match) {
+  switch ($route_name) {
+    case 'help.page.dgi_fixity':
+    case 'dgi_fixity.settings':
+      $output = array_fill(0, 2, ['#type' => 'html_tag', '#tag' => 'p']);
+      $output[0]['#value'] = new TranslatableMarkup(
+        'The Fixity module validates selected files by generating hashes and comparing it against stored values produced by the <a href="@file_hash">File Hash module</a> for selected files uploaded to the site.',
+        ['@file_hash' => URL::fromRoute('help.page', ['name' => 'filehash'])->toString()],
+      );
+      return $output;
+  }
+}

dgi_fixity.permissions.yml

@@ -0,0 +1,4 @@
+administer fixity checks:
+  title: 'Administer Fixity Checks'
+view fixity checks:
+  title: 'View Fixity Checks'

dgi_fixity.routing.yml

@@ -0,0 +1,52 @@
+dgi_fixity.settings:
+  path: '/admin/config/fixity'
+  defaults:
+    _form: '\Drupal\dgi_fixity\Form\SettingsForm'
+    _title: 'Fixity'
+  requirements:
+    _permission: 'access administration pages,administer fixity checks'
+
+dgi_fixity.batch:
+  path: '/admin/config/fixity/check'
+  defaults:
+    _form: '\Drupal\dgi_fixity\Form\BatchForm'
+    _title: 'Check'
+  requirements:
+    _permission: 'access administration pages,administer fixity checks'
+
+dgi_fixity.generate:
+  path: '/admin/config/fixity/generate'
+  defaults:
+    _form: '\Drupal\dgi_fixity\Form\GenerateForm'
+    _title: 'Generate'
+  requirements:
+    _permission: 'access administration pages,administer fixity checks'
+
+entity.fixity_check.revision:
+  path: '/fixity/{fixity_check}/revisions/{fixity_check_revision}'
+  defaults:
+    _controller: '\Drupal\Core\Entity\Controller\EntityViewController::viewRevision'
+    _title_callback: '\Drupal\Core\Entity\Controller\EntityController::title'
+  requirements:
+    _permission: 'view fixity checks'
+    fixity_check: \d+
+    fixity_check_revision: \d+
+  options:
+    _admin_route: TRUE
+    parameters:
+      fixity_check:
+        type: entity:fixity_check
+      fixity_check_revision:
+        type: entity_revision:fixity_check
+
+entity.fixity_check.revision_delete_confirm:
+  path: '/fixity/{fixity_check}/revisions/{fixity_check_revision}/delete'
+  defaults:
+    _form: '\Drupal\dgi_fixity\Form\RevisionDeleteForm'
+    _title: 'Delete earlier check'
+  requirements:
+    _permission: 'administer fixity checks'
+    fixity_check: \d+
+    fixity_check_revision: \d+
+  options:
+    _admin_route: TRUE

dgi_fixity.services.yml

@@ -0,0 +1,18 @@
+services:
+  logger.channel.dgi_fixity:
+    class: Drupal\Core\Logger\LoggerChannel
+    factory: logger.factory:get
+    arguments: ['dgi_fixity']
+  dgi_fixity.fixity_check:
+    class: Drupal\dgi_fixity\FixityCheckService
+    arguments: ['@string_translation', '@config.factory', '@entity_type.manager', '@datetime.time', '@plugin.manager.mail', '@logger.channel.dgi_fixity', '@filehash']
+  dgi_fixity.route_subscriber:
+    class: Drupal\dgi_fixity\Routing\FixityCheckRouteSubscriber
+    arguments: ['@entity_type.manager', '@dgi_fixity.fixity_check']
+    tags:
+      - { name: event_subscriber }
+  dgi_fixity.paramconverter.fixity:
+    class: Drupal\dgi_fixity\Routing\FixityCheckConverter
+    arguments: ['@entity_type.manager', '@entity.repository', '@dgi_fixity.fixity_check']
+    tags:
+      - { name: paramconverter }

dgi_fixity.views.inc

@@ -0,0 +1,56 @@
+<?php
+
+/**
+ * @file
+ * Provide views data for file.module.
+ */
+
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Implements hook_views_data_alter().
+ */
+function dgi_fixity_views_data_alter(&$data) {
+  // Reverse relationship on fixity_check.file to file_managed.fid.
+  $field_id = 'file';
+  $entity_type_id = 'fixity_check';
+
+  $entity_type_manager = \Drupal::entityTypeManager();
+  $entity_type = $entity_type_manager->getDefinition($entity_type_id);
+
+  /** @var \Drupal\Core\Entity\EntityFieldManager $entity_field_manager */
+  $entity_field_manager = \Drupal::service('entity_field.manager');
+  $field_definitions = $entity_field_manager->getBaseFieldDefinitions($entity_type_id);
+  $field_type = $field_definitions[$field_id];
+
+  // Allow relations to both the entity and revision base table.
+  // The fixity_check entity does use data tables.
+  $tables = [$entity_type->getBaseTable(), $entity_type->getRevisionTable()];
+  foreach ($tables as $table) {
+    $group = $data[$table]['table']['group'];
+    $pseudo_field_name = 'reverse_' . $field_type->getName() . '_' . $table;
+    $data['file_managed'][$pseudo_field_name] = [
+      'real field' => $field_type->getName(),
+      'relationship' => [
+        'title' => new TranslatableMarkup('@entity using @field',
+          [
+            '@entity' => $entity_type->getLabel(),
+            '@field' => $field_type->getLabel(),
+          ],
+        ),
+        'label' => $group,
+        'help' => new TranslatableMarkup('Relate each @entity with a @field set to the file.',
+          [
+            '@entity' => $entity_type->getLabel(),
+            '@field' => $field_type->getLabel(),
+          ],
+        ),
+        'group' => $group,
+        'id' => 'standard',
+        'base' => $table,
+        'base field' => $field_type->getName(),
+        'relationship field' => 'fid',
+      ],
+    ];
+  }
+}

drush.services.yml

@@ -0,0 +1,6 @@
+services:
+  dgi_fixity.commands.fixity_check:
+    class: \Drupal\dgi_fixity\Commands\FixityCheck
+    arguments: ['@string_translation', '@logger.dblog', '@entity_type.manager']
+    tags:
+      - { name: drush.command }

src/Commands/FixityCheck.php

@@ -0,0 +1,113 @@
+<?php
+
+namespace Drupal\dgi_fixity\Commands;
+
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\Core\StringTranslation\TranslationInterface;
+use Drupal\dgi_fixity\FixityCheckBatchCheck;
+use Drupal\dgi_fixity\FixityCheckBatchGenerate;
+use Drush\Commands\DrushCommands;
+use Psr\Log\LoggerInterface;
+
+/**
+ * Drush command to perform fixity checks.
+ */
+class FixityCheck extends DrushCommands {
+
+  use StringTranslationTrait;
+
+  /**
+   * A logger instance.
+   *
+   * @var \Psr\Log\LoggerInterface
+   */
+  protected $logger;
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * Creates the drush command object.
+   *
+   * @param \Drupal\Core\StringTranslation\TranslationInterface $string_translation
+   *   The translation manager.
+   * @param \Psr\Log\LoggerInterface $logger
+   *   A logger instance.
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity manager.
+   */
+  public function __construct(TranslationInterface $string_translation, LoggerInterface $logger, EntityTypeManagerInterface $entity_type_manager) {
+    parent::__construct();
+    $this->stringTranslation = $string_translation;
+    $this->logger = $logger;
+    $this->entityTypeManager = $entity_type_manager;
+  }
+
+  /**
+   * Sets the periodic check flag to FALSE for all files.
+   *
+   * @command dgi_fixity:clear
+   */
+  public function clear() {
+    /** @var \Drupal\dgi_fixity\FixityCheckStorageInterface $storage */
+    $storage = $this->entityTypeManager->getStorage('fixity_check');
+    $count = $storage->countPeriodic();
+    if ($this->io()->confirm("This will remove periodic checks on ${count} files, are you sure?", FALSE)) {
+      $storage->clearPeriodic();
+    }
+  }
+
+  /**
+   * Creates a fixity_check entity for all previously created files.
+   *
+   * @command dgi_fixity:generate
+   */
+  public function generate() {
+    $batch = FixityCheckBatchGenerate::build();
+    batch_set($batch);
+    drush_backend_batch_process();
+  }
+
+  /**
+   * Perform fixity checks on files.
+   *
+   * @option fids   Comma separated list of file identifiers, or a path to a
+   *                file containing file identifiers. The file should have each
+   *                fid separated by a new line. If not specified the modules
+   *                settings for sources is used to determine which files to
+   *                check.
+   * @option force  Skip time elapsed threshold check when processing files.
+   *
+   * @command dgi_fixity:check
+   */
+  public function check(array $options = [
+    'fids' => NULL,
+    'force' => FALSE,
+  ]) {
+    $fids = $options['fids'];
+    if (!is_null($fids)) {
+      // If a file path is provided, parse it.
+      if (is_file($fids)) {
+        if (is_readable($fids)) {
+          $fids = explode("\n", trim(file_get_contents($fids)));
+        }
+        else {
+          $this->logger->error($this->t('Cannot read file @file', ['@file' => $fids]));
+          return;
+        }
+      }
+      else {
+        $fids = explode(',', $fids);
+      }
+    }
+    $batch = FixityCheckBatchCheck::build($fids, $options['force']);
+    batch_set($batch);
+    drush_backend_batch_process();
+  }
+
+}

src/Controller/FixityCheckController.php

@@ -0,0 +1,266 @@
+<?php
+
+namespace Drupal\dgi_fixity\Controller;
+
+use Drupal\Core\Controller\ControllerBase;
+use Drupal\Core\Datetime\DateFormatterInterface;
+use Drupal\Core\Entity\EntityStorageInterface;
+use Drupal\Core\Link;
+use Drupal\Core\Render\RendererInterface;
+use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\Core\Url;
+use Drupal\dgi_fixity\FixityCheckInterface;
+use Drupal\dgi_fixity\FixityCheckServiceInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Controller for fixity_check tasks.
+ */
+class FixityCheckController extends ControllerBase {
+
+  /**
+   * The date formatter service.
+   *
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
+   */
+  protected $dateFormatter;
+
+  /**
+   * The renderer service.
+   *
+   * @var \Drupal\Core\Render\RendererInterface
+   */
+  protected $renderer;
+
+  /**
+   * The fixity check service.
+   *
+   * @var \Drupal\dgi_fixity\FixityCheckServiceInterface
+   */
+  protected $fixity;
+
+  /**
+   * Constructs a controller for displaying fixity_check related tasks.
+   *
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
+   *   The date formatter service.
+   * @param \Drupal\Core\Render\RendererInterface $renderer
+   *   The renderer service.
+   * @param \Drupal\dgi_fixity\FixityCheckServiceInterface $fixity
+   *   The fixity service.
+   */
+  public function __construct(DateFormatterInterface $date_formatter, RendererInterface $renderer, FixityCheckServiceInterface $fixity) {
+    $this->dateFormatter = $date_formatter;
+    $this->renderer = $renderer;
+    $this->fixity = $fixity;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('date.formatter'),
+      $container->get('renderer'),
+      $container->get('dgi_fixity.fixity_check'),
+    );
+  }
+
+  /**
+   * Returns the audit display for the current entity.
+   *
+   * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
+   *   A RouteMatch object.
+   *
+   * @return array
+   *   Array of page elements to render.
+   */
+  public function entityAudit(RouteMatchInterface $route_match) {
+    $entity = $this->getEntityFromRouteMatch($route_match);
+    return $this->audit($entity);
+  }
+
+  /**
+   * Generates an overview table of all revisions of a given fixity_check.
+   *
+   * @param \Drupal\dgi_fixity\FixityCheckInterface $fixity_check
+   *   A fixity_check entity.
+   *
+   * @return array
+   *   An array expected by \Drupal\Core\Render\RendererInterface::render().
+   */
+  public function audit(FixityCheckInterface $fixity_check) {
+    $account = $this->currentUser();
+    $storage = $this->entityTypeManager()->getStorage('fixity_check');
+
+    $build['#title'] = $this->t('Audit for %title', [
+      '%title' => $fixity_check->label(),
+    ]);
+
+    $header = [
+      $this->t('Performed'),
+      $this->t('State'),
+      $this->t('Operations'),
+    ];
+
+    $canDelete = $account->hasPermission('administer fixity checks') && $fixity_check->access('delete');
+
+    $rows = [];
+    $defaultRevision = $fixity_check->getRevisionId();
+    $currentRevisionDisplayed = FALSE;
+
+    foreach ($this->getRevisionIds($fixity_check, $storage) as $revision_id) {
+      /** @var \Drupal\dgi_fixity\FixityCheckInterface $revision */
+      $revision = $storage->loadRevision($revision_id);
+
+      // Use timestamp rather than timestamp_ago to allow for caching.
+      $date = ($revision->wasPerformed()) ?
+       $revision->performed->view([
+         'label' => 'hidden',
+         'type' => 'timestamp',
+       ]) :
+       $this->t('never');
+
+      $isCurrentRevision = $revision_id == $defaultRevision || (!$currentRevisionDisplayed && $revision->wasDefaultRevision());
+      if (!$isCurrentRevision) {
+        $link = Link::fromTextAndUrl($date, new Url(
+          'entity.fixity_check.revision',
+          [
+            'fixity_check' => $fixity_check->id(),
+            'fixity_check_revision' => $revision_id,
+          ]
+        ))->toString();
+      }
+      else {
+        $link = $fixity_check->toLink($date)->toString();
+        $currentRevisionDisplayed = TRUE;
+      }
+
+      $state = $revision->state->view([
+        'label' => 'hidden',
+        'type' => 'dgi_fixity_state',
+      ]);
+
+      $row = [
+        [
+          'data' => [
+            '#markup' => $link,
+          ],
+        ],
+        [
+          'data' => [
+            '#markup' => $this->renderer->renderRoot($state),
+          ],
+        ],
+      ];
+
+      if ($isCurrentRevision) {
+        $row[] = [
+          'data' => [
+            '#prefix' => '<em>',
+            '#markup' => $this->t('Current revision'),
+            '#suffix' => '</em>',
+          ],
+        ];
+
+        $rows[] = [
+          'data' => $row,
+          'class' => ['revision-current'],
+        ];
+      }
+      else {
+        $links = [];
+
+        if ($canDelete) {
+          $links['delete'] = [
+            'title' => $this->t('Delete'),
+            'url' => Url::fromRoute(
+              'entity.fixity_check.revision_delete_confirm',
+              [
+                'fixity_check' => $fixity_check->id(),
+                'fixity_check_revision' => $revision_id,
+              ]
+            ),
+          ];
+        }
+
+        $row[] = [
+          'data' => [
+            '#type' => 'operations',
+            '#links' => $links,
+          ],
+        ];
+
+        $rows[] = $row;
+      }
+    }
+
+    $build['fixity_check_revisions_table'] = [
+      '#theme' => 'table',
+      '#rows' => $rows,
+      '#header' => $header,
+      '#attributes' => [
+        'class' => 'fixity_check-revision-table',
+      ],
+    ];
+    $build['pager'] = [
+      '#type' => 'pager',
+    ];
+
+    $build['#cache'] = [
+      'keys' => [
+        'entity_view', 'fixity_check', $fixity_check->id(), 'revisions',
+      ],
+      'contexts' => [
+        // Date displayed varies by timezone.
+        'timezone',
+      ],
+      'tags' => [
+        // Invalidated by revision create/delete hooks.
+        'fixity_check:' . $fixity_check->id() . ':revisions_list',
+      ],
+      'bin' => 'render',
+    ];
+    $this->renderer->addCacheableDependency($build, $fixity_check);
+    return $build;
+  }
+
+  /**
+   * Gets a list of fixity_check revision IDs for a given fixity_check.
+   *
+   * @param \Drupal\dgi_fixity\FixityCheckInterface $fixity_check
+   *   Media entity to search for revisions.
+   * @param \Drupal\Core\Entity\EntityStorageInterface $storage
+   *   Media storage to load revisions from.
+   *
+   * @return int[]
+   *   fixity_check revision IDs in descending order.
+   */
+  protected function getRevisionIds(FixityCheckInterface $fixity_check, EntityStorageInterface $storage) {
+    $result = $storage->getQuery()
+      ->allRevisions()
+      ->condition('id', $fixity_check->id())
+      ->sort('performed', 'DESC')
+      ->pager(50)
+      ->execute();
+    return array_keys($result);
+  }
+
+  /**
+   * Retrieves entity from route match.
+   *
+   * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
+   *   The route match.
+   *
+   * @return \Drupal\dgi_fixity\FixityCheckInterface|null
+   *   The fixity check entity from the passed-in route match.
+   */
+  protected function getEntityFromRouteMatch(RouteMatchInterface $route_match): ?FixityCheckInterface {
+    // Option added by Route Subscriber.
+    $parameter_name = $route_match->getRouteObject()->getOption('_fixity_entity_type_id');
+    return ($parameter_name == 'fixity_check') ?
+       $route_match->getParameter($parameter_name) :
+       $this->fixity->fromEntity($route_match->getParameter($parameter_name));
+  }
+
+}

src/Entity/FixityCheck.php

@@ -0,0 +1,335 @@
+<?php
+
+namespace Drupal\dgi_fixity\Entity;
+
+use Drupal\Core\Entity\ContentEntityBase;
+use Drupal\Core\Entity\EntityStorageInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Field\BaseFieldDefinition;
+use Drupal\Core\Language\LanguageInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\dgi_fixity\FixityCheckInterface;
+use Drupal\file\Entity\File;
+
+/**
+ * Defines the fixity_check entity class.
+ *
+ * @ContentEntityType(
+ *   id = "fixity_check",
+ *   label = @Translation("Fixity Check"),
+ *   label_collection = @Translation("Audit"),
+ *   label_singular = @Translation("Fixity Check"),
+ *   label_plural = @Translation("Fixity Checks"),
+ *   label_count = @PluralTranslation(
+ *     singular = "@count Fixity Check",
+ *     plural = "@count Fixity Checks"
+ *   ),
+ *   handlers = {
+ *     "storage" = "Drupal\dgi_fixity\FixityCheckStorage",
+ *     "storage_schema" = "Drupal\dgi_fixity\FixityCheckStorageSchema",
+ *     "list_builder" = "Drupal\dgi_fixity\FixityCheckListBuilder",
+ *     "views_data" = "Drupal\dgi_fixity\FixityCheckViewsData",
+ *     "access" = "Drupal\dgi_fixity\FixityCheckAccessControlHandler",
+ *     "form" = {
+ *       "edit" = "Drupal\Core\Entity\ContentEntityForm",
+ *       "fixity-check" = "Drupal\dgi_fixity\Form\CheckForm",
+ *       "delete" = "Drupal\Core\Entity\ContentEntityDeleteForm",
+ *       "delete-multiple-confirm" = "Drupal\Core\Entity\Form\DeleteMultipleForm",
+ *     },
+ *     "route_provider" = {
+ *       "html" = "Drupal\dgi_fixity\Routing\FixityCheckRouteProvider"
+ *     },
+ *   },
+ *   base_table = "fixity_check",
+ *   revision_table = "fixity_check_revision",
+ *   show_revision_ui = FALSE,
+ *   translatable = FALSE,
+ *   common_reference_target = FALSE,
+ *   entity_keys = {
+ *     "id" = "id",
+ *     "revision" = "revision_id",
+ *   },
+ *   links = {
+ *     "canonical" = "/fixity/{fixity_check}",
+ *     "edit-form" = "/fixity/{fixity_check}/edit",
+ *     "fixity-audit" = "/fixity/{fixity_check}/audit",
+ *     "fixity-check" = "/fixity/{fixity_check}/check",
+ *     "delete-form" = "/fixity/{fixity_check}/delete",
+ *     "delete-multiple-form" = "/fixity/delete",
+ *     "collection" = "/admin/reports/fixity",
+ *   },
+ *   admin_permission = "administer fixity checks",
+ * )
+ */
+class FixityCheck extends ContentEntityBase implements FixityCheckInterface {
+
+  use StringTranslationTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {
+    $fields = parent::baseFieldDefinitions($entity_type);
+
+    $fields['file'] = BaseFieldDefinition::create('entity_reference')
+      ->setLabel(new TranslatableMarkup('File'))
+      ->setDescription(new TranslatableMarkup('The file entity the fixity check was performed against.'))
+      ->setRequired(TRUE)
+      ->setRevisionable(FALSE)
+      ->setTranslatable(FALSE)
+      // It's not possible to have two fixity checks for the same file, they
+      // should result in different versions of the same fixity_check entity.
+      ->addConstraint('UniqueFieldEntityReference')
+      ->setSetting('target_type', 'file')
+      ->setDisplayConfigurable('view', FALSE)
+      ->setDisplayOptions('view', [
+        'type' => 'dgi_fixity_file_reference',
+        'weight' => 0,
+      ]);
+
+    $fields['state'] = BaseFieldDefinition::create('integer')
+      ->setLabel(new TranslatableMarkup('State'))
+      ->setDescription(new TranslatableMarkup('A flag indicating the state of the whether the check passed or not.'))
+      ->setTranslatable(FALSE)
+      ->setRevisionable(TRUE)
+      ->setInitialValue(static::STATE_UNDEFINED)
+      ->setDefaultValue(static::STATE_UNDEFINED)
+      // Define this via an options provider once.
+      // https://www.drupal.org/node/2329937 is completed.
+      ->addPropertyConstraints('value', [
+        'AllowedValues' => ['callback' => static::class . '::getAllowedStates'],
+      ])
+      ->setDisplayConfigurable('view', FALSE)
+      ->setDisplayOptions('view', [
+        'type' => 'dgi_fixity_state',
+        'weight' => 1,
+      ]);
+
+    // A value of 0 indicates the check was never performed even though it is
+    // a unix-timestamp, which means it is technically 1970-01-01 00:00:00.
+    $fields['performed'] = BaseFieldDefinition::create('timestamp')
+      ->setLabel(t('Performed'))
+      ->setDescription(t('The time the check was performed, 0 if never performed.'))
+      ->setTranslatable(FALSE)
+      ->setRevisionable(TRUE)
+      ->setInitialValue(0)
+      ->setDefaultValue(0)
+      ->setDisplayConfigurable('view', FALSE)
+      ->setDisplayOptions('view', [
+        'type' => 'timestamp_ago',
+        'weight' => 2,
+      ]);
+
+    $fields['periodic'] = BaseFieldDefinition::create('boolean')
+      ->setLabel(t('Periodic'))
+      ->setDescription(t('Enable/disable periodic fixity checks.'))
+      ->setRequired(TRUE)
+      ->setTranslatable(FALSE)
+      ->setRevisionable(FALSE)
+      ->setInitialValue(FALSE)
+      ->setDefaultValue(FALSE)
+      ->setDisplayConfigurable('view', FALSE)
+      ->setDisplayOptions('form', [
+        'type' => 'options_buttons',
+        'weight' => 3,
+      ])
+      ->setDisplayOptions('view', [
+        'type' => 'boolean',
+        'weight' => 3,
+      ]);
+
+    $fields['queued'] = BaseFieldDefinition::create('timestamp')
+      ->setLabel(t('Queued'))
+      ->setDescription(t('Time when this file was queued for fixity, 0 if not queued.'))
+      ->setTranslatable(FALSE)
+      ->setRevisionable(FALSE)
+      ->setInitialValue(0)
+      ->setDefaultValue(0)
+      ->setDisplayConfigurable('view', FALSE)
+      ->setDisplayOptions('view', [
+        'region' => 'hidden',
+      ]);
+
+    return $fields;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function preSave(EntityStorageInterface $storage) {
+    parent::preSave($storage);
+    // Disallow changes to state / performed on existing revisions.
+    // Unless this is the first revision and it the check was never performed.
+    if (!$this->isNewRevision() && !($this->isLatestRevision() && !$this->original->wasPerformed())) {
+      $immutable_fields = ['state', 'performed'];
+      foreach ($immutable_fields as $field) {
+        if ($this->{$field}->hasAffectingChanges($this->original->{$field}, LanguageInterface::LANGCODE_NOT_SPECIFIED)) {
+          throw new \LogicException("Entity type {$this->getEntityTypeId()} does not support modifying the '{$field}' field of existing revisions.");
+        }
+      }
+    }
+    // The file field is immutable after creation.
+    if ($this->original && $this->file->hasAffectingChanges($this->original->file, LanguageInterface::LANGCODE_NOT_SPECIFIED)) {
+      throw new \LogicException("Entity type {$this->getEntityTypeId()} does not support modifying the file field after creation.");
+    }
+    // If performed has changed force queued to zero.
+    if ($this->original && $this->performed->hasAffectingChanges($this->original->performed, LanguageInterface::LANGCODE_NOT_SPECIFIED)) {
+      $this->setQueued(0);
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function preSaveRevision(EntityStorageInterface $storage, \stdClass $record) {
+    parent::preSaveRevision($storage, $record);
+    // Disallow creating revisions if performed is not set.
+    if (!$this->isNew() && $this->isNewRevision() && $record->performed === 0) {
+      throw new \LogicException("Entity type {$this->getEntityTypeId()} does not support creating new revisions without where the performed field is not set.");
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setNewRevision($value = TRUE) {
+    parent::setNewRevision($value);
+    // Reset the state and performed timestamp when creating a new revision
+    // from an existing fixity_check.
+    if (!$this->isNew() && $value) {
+      $this->state = static::STATE_UNDEFINED;
+      unset($this->performed);
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFile(): ?File {
+    /** @var \Drupal\Core\Field\EntityReferenceFieldItemList $file */
+    $file = $this->file;
+    return $file->isEmpty() ? NULL : $file->referencedEntities()[0];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setFile(File $file): FixityCheckInterface {
+    $this->set('file', $file);
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getState(): int {
+    return $this->state->value;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setState(int $state): FixityCheckInterface {
+    if (!in_array($state, static::getAllowedStates())) {
+      throw new \InvalidArgumentException("Invalid state '$state' has been given");
+    }
+    $this->set('state', $state);
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getStateLabel(): string {
+    return static::getStateProperty($this->getState(), 'label');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getStateProperty(int $state, string $property) {
+    return static::STATES[$state][$property] ?? NULL;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function passed(): bool {
+    $state = $this->getState();
+    return static::STATES[$state]['passed'] ?? FALSE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getPeriodic(): bool {
+    return $this->periodic->value;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setPeriodic(bool $periodic): FixityCheckInterface {
+    $this->set('periodic', $periodic);
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getPerformed(): int {
+    return $this->performed->value;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setPerformed(int $performed): FixityCheckInterface {
+    $this->set('performed', $performed);
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function wasPerformed(): bool {
+    return $this->getPerformed() !== 0;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getQueued(): int {
+    return $this->queued->value;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setQueued(int $queued): FixityCheckInterface {
+    $this->set('queued', $queued);
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function label() {
+    $file = $this->getFile();
+    return ($file === NULL) ?
+      $this->t('Fixity Check') :
+      $file->label();
+  }
+
+  /**
+   * Defines allowed states for AllowedValues constraints.
+   *
+   * @return int[]
+   *   The allowed states.
+   */
+  public static function getAllowedStates() {
+    return array_keys(static::STATES);
+  }
+
+}

src/EntityTypeInfo.php

@@ -0,0 +1,125 @@
+<?php
+
+namespace Drupal\dgi_fixity;
+
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Routing\RedirectDestinationInterface;
+use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\Core\StringTranslation\TranslationInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Manipulates entity type information.
+ *
+ * This class contains primarily bridged hooks for compile-time or
+ * cache-clear-time hooks. Runtime hooks should be placed in EntityOperations.
+ */
+class EntityTypeInfo implements ContainerInjectionInterface {
+
+  use StringTranslationTrait;
+
+  /**
+   * The current user.
+   *
+   * @var \Drupal\Core\Session\AccountInterface
+   */
+  protected $currentUser;
+
+  /**
+   * The redirect destination helper.
+   *
+   * @var \Drupal\Core\Routing\RedirectDestinationInterface
+   */
+  protected $redirect;
+
+  /**
+   * The fixity check service.
+   *
+   * @var \Drupal\dgi_fixity\FixityCheckServiceInterface
+   */
+  protected $fixity;
+
+  /**
+   * EntityTypeInfo constructor.
+   *
+   * @param \Drupal\Core\StringTranslation\TranslationInterface $string_translation
+   *   The translation manager.
+   * @param \Drupal\Core\Session\AccountInterface $current_user
+   *   Current user.
+   * @param \Drupal\Core\Routing\RedirectDestinationInterface $redirect
+   *   The redirect destination helper.
+   * @param \Drupal\dgi_fixity\FixityCheckServiceInterface $fixity
+   *   The fixity service.
+   */
+  public function __construct(TranslationInterface $string_translation, AccountInterface $current_user, RedirectDestinationInterface $redirect, FixityCheckServiceInterface $fixity) {
+    $this->stringTranslation = $string_translation;
+    $this->currentUser = $current_user;
+    $this->redirect = $redirect;
+    $this->fixity = $fixity;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('string_translation'),
+      $container->get('current_user'),
+      $container->get('redirect.destination'),
+      $container->get('dgi_fixity.fixity_check'),
+    );
+  }
+
+  /**
+   * Gets fixity check links to appropriate entity types.
+   *
+   * This is an alter hook bridge.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeInterface[] $entity_types
+   *   The master entity type list to alter.
+   *
+   * @see hook_entity_type_alter()
+   */
+  public function entityTypeAlter(array &$entity_types) {
+    $supported_entity_types = $this->fixity->fromEntityTypes();
+    foreach ($supported_entity_types as $entity_type_id) {
+      $entity_type = &$entity_types[$entity_type_id];
+      $entity_type->setLinkTemplate('fixity-audit', "/fixity/$entity_type_id/{{$entity_type_id}}");
+      $entity_type->setLinkTemplate('fixity-check', "/fixity/$entity_type_id/{{$entity_type_id}}/check");
+      $entity_type->setFormClass('fixity-check', 'Drupal\dgi_fixity\Form\CheckForm');
+    }
+  }
+
+  /**
+   * Gets fixity operations on entities that support it.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   The entity on which to define an operation.
+   *
+   * @return array
+   *   An array of operation definitions.
+   *
+   * @see hook_entity_operation()
+   */
+  public function entityOperation(EntityInterface $entity) {
+    $operations = [];
+    if ($entity->hasLinkTemplate('fixity-audit') && $this->currentUser->hasPermission('view fixity checks')) {
+      $operations['fixity-audit'] = [
+        'title' => $this->t('Audit'),
+        'weight' => 10,
+        'url' => $entity->toUrl('fixity-audit'),
+      ];
+      if ($entity->hasLinkTemplate('fixity-check') && $this->currentUser->hasPermission('administer fixity checks')) {
+        $operations['fixity-check'] = [
+          'title' => $this->t('Check'),
+          'weight' => 13,
+          'url' => $entity->toUrl('fixity-check', ['query' => $this->redirect->getAsArray()]),
+        ];
+      }
+    }
+    return $operations;
+  }
+
+}

src/FixityCheckAccessControlHandler.php

@@ -0,0 +1,39 @@
+<?php
+
+namespace Drupal\dgi_fixity;
+
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Entity\EntityAccessControlHandler;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Session\AccountInterface;
+
+/**
+ * Defines an access control handler for fixity_check entities.
+ */
+class FixityCheckAccessControlHandler extends EntityAccessControlHandler {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function checkAccess(EntityInterface $entity, $operation, AccountInterface $account) {
+    if ($account->hasPermission($this->entityType->getAdminPermission())) {
+      return AccessResult::allowed()->cachePerPermissions();
+    }
+
+    switch ($operation) {
+      case 'view':
+        return AccessResult::allowedIfHasPermission($account, 'view fixity checks')->cachePerPermissions();
+
+      default:
+        return AccessResult::forbidden()->cachePerPermissions();
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function checkCreateAccess(AccountInterface $account, array $context, $entity_bundle = NULL) {
+    return AccessResult::allowedIfHasPermission($account, $this->entityType->getAdminPermission());
+  }
+
+}

src/FixityCheckBatchCheck.php

@@ -0,0 +1,287 @@
+<?php
+
+namespace Drupal\dgi_fixity;
+
+use Drupal\Core\Batch\BatchBuilder;
+use Drupal\Core\StringTranslation\PluralTranslatableMarkup;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\dgi_fixity\Form\SettingsForm;
+
+/**
+ * Performs fixity checks.
+ */
+class FixityCheckBatchCheck {
+
+  /**
+   * Creates a batch for performing fixity checks.
+   *
+   * @param int[] $fids
+   *   A list of file identifiers, if not specified files with periodic checks
+   *   enabled will be selected.
+   * @param bool $force
+   *   A flag to indicate if the check should be performed even if the time
+   *   elapsed since the last check has not exceed the required threshold.
+   * @param int $batch_size
+   *   The number of of files to process at a time.
+   *   If not specified it will default to the modules configuration.
+   */
+  public static function build(array $fids = NULL, bool $force = FALSE, int $batch_size = NULL) {
+    $batch_size = is_null($batch_size) ? \Drupal::config(SettingsForm::CONFIG_NAME)->get(SettingsForm::BATCH_SIZE) : $batch_size;
+    return is_null($fids) ?
+      static::buildPeriodic($force, $batch_size) :
+      static::buildFixed($fids, $force, $batch_size);
+  }
+
+  /**
+   * Creates a batch for processing a fixed list of file identifiers.
+   */
+  protected static function buildFixed(array $fids, bool $force, int $batch_size) {
+    $builder = new BatchBuilder();
+    return $builder
+      ->setTitle(new TranslatableMarkup('Performing checks on @count file(s)', ['@count' => count($fids)]))
+      ->setInitMessage(new TranslatableMarkup('Starting'))
+      ->setErrorMessage(new TranslatableMarkup('Batch has encountered an error'))
+      ->addOperation([static::class, 'processFixedList'], [
+        $fids,
+        $force,
+        $batch_size,
+      ])
+      ->setFinishCallback([static::class, 'finished'])
+      ->toArray();
+  }
+
+  /**
+   * Creates a batch for processing files that have periodic checks enabled.
+   */
+  public static function buildPeriodic(bool $force, int $batch_size) {
+    $sources = \Drupal::config(SettingsForm::CONFIG_NAME)->get(SettingsForm::SOURCES);
+    if (empty($sources)) {
+      throw new \InvalidArgumentException("No sources specified, check the modules configuration.");
+    }
+    $builder = new BatchBuilder();
+    foreach ($sources as $source) {
+      $builder->addOperation(
+        [static::class, 'processSource'],
+        [$source, $batch_size],
+      );
+    }
+    return $builder
+      ->setTitle(new TranslatableMarkup('Enumerating periodic checks from @count Source(s)', ['@count' => count($sources)]))
+      ->setInitMessage(new TranslatableMarkup('Starting'))
+      ->setErrorMessage(new TranslatableMarkup('Batch has encountered an error'))
+      ->addOperation([static::class, 'processPeriodic'], [$force, $batch_size])
+      ->setFinishCallback([static::class, 'finished'])
+      ->toArray();
+  }
+
+  /**
+   * Check the given files.
+   *
+   * @param int[] $fids
+   *   A list of file identifiers.
+   * @param bool $force
+   *   A flag to indicate if the check should be performed even if the time
+   *   elapsed since the last check has not exceed the required threshold.
+   * @param int $batch_size
+   *   The amount of files each time this process runs.
+   * @param array|object $context
+   *   Context for operations.
+   */
+  public static function processFixedList(array $fids, bool $force, int $batch_size, &$context) {
+    $sandbox = &$context['sandbox'];
+    $results = &$context['results'];
+    if (!isset($sandbox['total'])) {
+      $sandbox['offset'] = 0;
+      $sandbox['total'] = count($fids);
+      $results['successful'] = 0;
+      $results['ignored'] = 0;
+      $results['skipped'] = 0;
+      $results['failed'] = 0;
+      $results['errors'] = [];
+    }
+    $chunk = array_slice($fids, $sandbox['offset'], $batch_size);
+    $end = min($sandbox['total'], $sandbox['offset'] + count($chunk));
+    $context['message'] = new TranslatableMarkup('Processing @start to @end of @total', [
+      '@start' => $sandbox['offset'],
+      '@end' => $end,
+      '@total' => $sandbox['total'],
+    ]);
+    $files = \Drupal::service('entity_type.manager')->getStorage('file')->loadMultiple($chunk);
+    // It is possible for non existing fids to be listed in $chunk, in such
+    // cases this is ignored.
+    $results['ignored'] += count(array_diff($chunk, array_keys($files)));
+    static::check($files, $force, $results);
+    $sandbox['offset'] = $end;
+    $context['finished'] = $sandbox['offset'] / $sandbox['total'];
+  }
+
+  /**
+   * Enable periodic checks on files as returned by the give source view.
+   */
+  public static function processSource(string $source, $batch_size, &$context) {
+    $results = &$context['results'];
+    // Do not track success/failure on processing source, as that is done for
+    // checks only. Errors however do get passed though.
+    if (!isset($results['errors'])) {
+      $results['errors'] = [];
+    }
+
+    /** @var \Drupal\dgi_fixity\FixityCheckServiceInterface $fixity */
+    $fixity = \Drupal::service('dgi_fixity.fixity_check');
+    $view = $fixity->source($source, $batch_size);
+    $view->execute();
+    // Only processes those which have not already enabled periodic checks.
+    foreach ($view->result as $row) {
+      try {
+        /** @var \Drupal\dgi_fixity\FixityCheckInterface $check */
+        $check = $view->field['periodic']->getEntity($row);
+        $check->setPeriodic(TRUE);
+        $check->save();
+      }
+      catch (\Exception $e) {
+        $results['errors'][] = new TranslatableMarkup('Encountered an exception: @exception', [
+          '@exception' => $e,
+        ]);
+        // In practice exceptions in this case shouldn't arise, but if they do
+        // exit to prevent an infinite loop by exiting the operation.
+        $context['finished'] = 1;
+        return;
+      }
+    }
+    // End when we have exhausted all inputs.
+    $context['finished'] = count($view->result) == 0;
+  }
+
+  /**
+   * Checks all files which have enabled periodic fixity checks.
+   *
+   * @param bool $force
+   *   A flag to indicate if the check should be performed even if the time
+   *   elapsed since the last check has not exceed the required threshold.
+   * @param int $batch_size
+   *   The amount of files each time this process runs.
+   * @param array|object $context
+   *   Context for operations.
+   */
+  public static function processPeriodic(bool $force, int $batch_size, &$context) {
+    /** @var \Drupal\dgi_fixity\FixityCheckStorageInterface $storage */
+    $storage = \Drupal::entityTypeManager()->getStorage('fixity_check');
+
+    $sandbox = &$context['sandbox'];
+    $results = &$context['results'];
+    if (!isset($sandbox['offset'])) {
+      $sandbox['offset'] = 0;
+      $sandbox['remaining'] = $storage->countPeriodic();
+      $results['successful'] = 0;
+      $results['ignored'] = 0;
+      $results['skipped'] = 0;
+      $results['failed'] = 0;
+      $results['errors'] = $results['errors'] ?? [];
+    }
+
+    $files = $storage->getPeriodic($sandbox['offset'], $batch_size);
+    $end = min($sandbox['total'], $sandbox['offset'] + count($files));
+    $context['message'] = new TranslatableMarkup('Processing @start to @end', [
+      '@start' => $sandbox['offset'],
+      '@end' => $end,
+    ]);
+    static::check($files, $force, $results);
+    $sandbox['offset'] = $end;
+
+    $remaining = $storage->countPeriodic();
+    $progress_halted = $sandbox['remaining'] == $remaining;
+    $sandbox['remaining'] = $remaining;
+
+    // End when we have exhausted all inputs or progress has halted.
+    $context['finished'] = empty($files) || $progress_halted;
+  }
+
+  /**
+   * Performs a fixity check on the given list of files.
+   *
+   * @param \Drupal\file\FileInterface[] $files
+   *   A list of file identifiers.
+   * @param bool $force
+   *   A flag to indicate if the check should be performed even if the time
+   *   elapsed since the last check has not exceed the required threshold.
+   * @param array &$results
+   *   An associative array with the results of the fixity checks
+   *   - missing: The number of file identifiers for which no files exist.
+   *   - successful: The number of files that were successfully checked.
+   *   - errors: A list of error messages if any occurred.
+   */
+  protected static function check(array $files, bool $force, array &$results) {
+    /** @var \Drupal\dgi_fixity\FixityCheckServiceInterface $fixity */
+    $fixity = \Drupal::service('dgi_fixity.fixity_check');
+    foreach ($files as $file) {
+      try {
+        $result = $fixity->check($file, $force);
+        if ($result instanceof FixityCheckInterface) {
+          if ($result->passed()) {
+            $results['successful']++;
+          }
+        }
+        else {
+          // The check was not performed as the time elapsed since the last
+          // check did not exceed the required threshold.
+          $results['skipped']++;
+        }
+      }
+      catch (\Exception $e) {
+        $results['failed']++;
+        $results['errors'][] = new TranslatableMarkup('Encountered an exception: @exception', [
+          '@exception' => $e,
+        ]);
+      }
+    }
+  }
+
+  /**
+   * Batch Finished callback.
+   *
+   * @param bool $success
+   *   Success of the operation.
+   * @param array $results
+   *   Array of results for post processing.
+   * @param array $operations
+   *   Array of operations.
+   */
+  public static function finished($success, array $results, array $operations) {
+    $messenger = \Drupal::messenger();
+    $messenger->addStatus(new PluralTranslatableMarkup(
+      $results['successful'] + $results['ignored'] + $results['skipped'] + $results['failed'],
+      'Processed @count item in total.',
+      'Processed @count items in total.'
+    ));
+    $messenger->addStatus(new PluralTranslatableMarkup(
+      $results['successful'],
+      '@count was successful.',
+      '@count were successful.',
+    ));
+    $messenger->addStatus(new PluralTranslatableMarkup(
+      $results['ignored'],
+      '@count was ignored.',
+      '@count were ignored.',
+    ));
+    $messenger->addStatus(new PluralTranslatableMarkup(
+      $results['skipped'],
+      '@count was skipped.',
+      '@count were skipped.',
+    ));
+    $messenger->addStatus(new TranslatableMarkup(
+      '@count failed.', ['@count' => $results['failed']]
+    ));
+    $error_count = count($results['errors']);
+    if ($error_count > 0) {
+      $messenger->addMessage(new PluralTranslatableMarkup(
+        $error_count,
+        '@count error occurred.',
+        '@count errors occurred.',
+      ));
+      foreach ($results['errors'] as $error) {
+        $messenger->addError($error);
+      }
+    }
+  }
+
+}

src/FixityCheckBatchGenerate.php

@@ -0,0 +1,118 @@
+<?php
+
+namespace Drupal\dgi_fixity;
+
+use Drupal\Core\Batch\BatchBuilder;
+use Drupal\Core\StringTranslation\PluralTranslatableMarkup;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\dgi_fixity\Form\SettingsForm;
+
+/**
+ * Generates a fixity_check for all previously created files.
+ */
+class FixityCheckBatchGenerate {
+
+  /**
+   * Creates a batch for this service.
+   *
+   * @param int $batch_size
+   *   The number of of files to process at a time.
+   *   If not specified it will default to the modules configuration.
+   */
+  public static function build($batch_size = NULL) {
+    if (is_null($batch_size)) {
+      $batch_size = \Drupal::config(SettingsForm::CONFIG_NAME)->get(SettingsForm::BATCH_SIZE);
+    }
+    $builder = new BatchBuilder();
+    return $builder
+      ->setTitle(new TranslatableMarkup('Generating Fixity Checks for previously created files'))
+      ->setInitMessage(new TranslatableMarkup('Starting'))
+      ->setErrorMessage(new TranslatableMarkup('Batch has encountered an error'))
+      ->addOperation([static::class, 'generate'], [$batch_size])
+      ->setFinishCallback([static::class, 'finished'])
+      ->toArray();
+  }
+
+  /**
+   * Generates fixity_check entity for previously created files.
+   *
+   * @param int $batch_size
+   *   The number of of files to process at a time.
+   * @param array|object $context
+   *   Context for operations.
+   */
+  public static function generate($batch_size, &$context) {
+    /** @var \Drupal\dgi_fixity\FixityCheckStorageInterface $storage */
+    $storage = \Drupal::entityTypeManager()->getStorage('fixity_check');
+
+    $sandbox = &$context['sandbox'];
+    $results = &$context['results'];
+    if (!isset($results['successful'])) {
+      $results['successful'] = 0;
+      $results['failed'] = 0;
+      $results['errors'] = [];
+      $sandbox['remaining'] = $storage->countMissing();
+    }
+
+    $files = $storage->getMissing(0, $batch_size);
+    foreach ($files as $file) {
+      $check = $storage->create(['file' => $file->id()]);
+      try {
+        $check->save();
+        $results['successful']++;
+      }
+      catch (\Exception $e) {
+        $results['failed']++;
+        $results['errors'][] = new TranslatableMarkup('Encountered an exception: @exception', [
+          '@exception' => $e,
+        ]);
+      }
+    }
+
+    $remaining = $storage->countMissing();
+    $progress_halted = $sandbox['remaining'] == $remaining;
+    $sandbox['remaining'] = $remaining;
+
+    // End when we have exhausted all inputs or progress has halted.
+    $context['finished'] = empty($files) || $progress_halted;
+  }
+
+  /**
+   * Batch Finished callback.
+   *
+   * @param bool $success
+   *   Success of the operation.
+   * @param array $results
+   *   Array of results for post processing.
+   * @param array $operations
+   *   Array of operations.
+   */
+  public static function finished($success, array $results, array $operations) {
+    $messenger = \Drupal::messenger();
+    $messenger->addStatus(new PluralTranslatableMarkup(
+      $results['successful'] + $results['failed'],
+      'Processed @count item in total.',
+      'Processed @count items in total.'
+    ));
+    $messenger->addStatus(new PluralTranslatableMarkup(
+      $results['successful'],
+      '@count was successful.',
+      '@count were successful.',
+    ));
+    $messenger->addStatus(new TranslatableMarkup(
+      '@count failed.', ['@count' => $results['failed']]
+    ));
+    $error_count = count($results['errors']);
+    if ($error_count > 0) {
+      $messenger->addMessage(new PluralTranslatableMarkup(
+        $error_count,
+        '@count error occurred.',
+        '@count errors occurred.',
+      ));
+      foreach ($results['errors'] as $error) {
+        $messenger->addError($error);
+      }
+    }
+  }
+
+}

src/FixityCheckInterface.php

@@ -0,0 +1,229 @@
+<?php
+
+namespace Drupal\dgi_fixity;
+
+use Drupal\Core\Entity\ContentEntityInterface;
+use Drupal\Core\Entity\RevisionableInterface;
+use Drupal\file\Entity\File;
+
+/**
+ * Provides an interface defining a fixity_check entity.
+ */
+interface FixityCheckInterface extends ContentEntityInterface, RevisionableInterface {
+
+  /**
+   * The check has not been performed or is some other undefined state.
+   */
+  const STATE_UNDEFINED = 0;
+
+  /**
+   * The generated checksums match the recorded values.
+   */
+  const STATE_MATCHES = 1;
+
+  /**
+   * The generated checksums do not match the recorded values.
+   */
+  const STATE_MISMATCHES = 2;
+
+  /**
+   * The file is missing.
+   */
+  const STATE_MISSING = 3;
+
+  /**
+   * One or more checksum(s) are missing from the files recorded checksums.
+   */
+  const STATE_NO_CHECKSUM = 4;
+
+  /**
+   * One or more checksum(s) could not be generated.
+   */
+  const STATE_GENERATION_FAILED = 5;
+
+  /**
+   * Properties of each state.
+   *
+   * @var array
+   *  An associative array with the following properties.
+   *   - label: The label to use when displaying a single check.
+   *   - singular: The singular label to use when aggregating checks.
+   *   - plural: The plural label to use when aggregating checks.
+   *   - passed: TRUE if this state indicates the check passed FALSE otherwise.
+   */
+  const STATES = [
+    self::STATE_UNDEFINED => [
+      'label' => 'Undefined',
+      'singular' => '@count check is undefined',
+      'plural' => '@count checks are undefined',
+      'passed' => FALSE,
+    ],
+    self::STATE_MATCHES => [
+      'label' => 'Matched recorded values',
+      'singular' => '@count check match the recorded checksum(s)',
+      'plural' => '@count checks matched the recorded checksum(s)',
+      'passed' => TRUE,
+    ],
+    self::STATE_MISMATCHES => [
+      'label' => 'Did not match recorded values',
+      'singular' => '@count check did not match the recorded checksum(s)',
+      'plural' => '@count checks did not match the recorded checksum(s)',
+      'passed' => FALSE,
+    ],
+    self::STATE_MISSING => [
+      'label' => 'Could not be performed: File missing',
+      'singular' => '@count file is missing and could not be checked',
+      'plural' => '@count files are missing and could not be checked',
+      'passed' => FALSE,
+    ],
+    self::STATE_NO_CHECKSUM => [
+      'label' => 'Could not be performed: Missing recorded checksum(s)',
+      'singular' => '@count file is missing a recorded checksum',
+      'plural' => '@count files are missing recorded checksums',
+      'passed' => FALSE,
+    ],
+    self::STATE_GENERATION_FAILED => [
+      'label' => 'Could not be performed: Could not generate checksum(s)',
+      'singular' => '@count check could not generate a checksum',
+      'plural' => '@count checks could not generate checksums',
+      'passed' => FALSE,
+    ],
+  ];
+
+  /**
+   * Gets the file this check was performed against.
+   *
+   * @return \Drupal\file\Entity\File
+   *   The file associated with this check or NULL if not set.
+   */
+  public function getFile(): ?File;
+
+  /**
+   * Sets the state of the check.
+   *
+   * @param \Drupal\file\Entity\File $file
+   *   The state of the check.
+   *
+   * @return $this
+   */
+  public function setFile(File $file): FixityCheckInterface;
+
+  /**
+   * Gets the state of the check.
+   *
+   * @return int
+   *   The state of the check.
+   */
+  public function getState(): int;
+
+  /**
+   * Sets the state of the check.
+   *
+   * @param int $state
+   *   The state of the check.
+   *
+   * @return $this
+   *
+   * @throws \InvalidArgumentException
+   *   If $state is not valid.
+   */
+  public function setState(int $state): FixityCheckInterface;
+
+  /**
+   * Gets the human readable representation of the state.
+   *
+   * @return string
+   *   The state.
+   */
+  public function getStateLabel(): string;
+
+  /**
+   * Gets the given property of the given state if defined.
+   *
+   * @param int $state
+   *   The state of whose properties are fetched.
+   * @param string $property
+   *   The property to get.
+   *
+   * @return mixed|null
+   *   The property if defined otherwise NULL.
+   *
+   * @see \Drupal\dgi_fixity\FixityCheckInterface::STATES
+   */
+  public static function getStateProperty(int $state, string $property);
+
+  /**
+   * Checks if the check passed.
+   *
+   * @see \Drupal\dgi_fixity\FixityCheckInterface::STATES
+   *
+   * @return bool
+   *   TRUE if the generated checksums match the recorded values, FALSE
+   *   otherwise.
+   */
+  public function passed(): bool;
+
+  /**
+   * Gets the timestamp of when the check was performed.
+   *
+   * @return int
+   *   The timestamp of the check. 0 indicates the check was not performed.
+   */
+  public function getPerformed(): int;
+
+  /**
+   * Sets the timestamp of when the check was performed.
+   *
+   * @param int $performed
+   *   The timestamp when the check was performed.
+   *
+   * @return $this
+   */
+  public function setPerformed(int $performed): FixityCheckInterface;
+
+  /**
+   * TRUE if this check was performed, FALSE otherwise.
+   *
+   * @return bool
+   *   TRUE if this check was performed, FALSE otherwise.
+   */
+  public function wasPerformed(): bool;
+
+  /**
+   * Checks if periodic checks are enabled.
+   *
+   * @return int
+   *   TRUE if periodic checks are enabled, FALSE otherwise.
+   */
+  public function getPeriodic(): bool;
+
+  /**
+   * Enable or disable periodic checks.
+   *
+   * @param bool $periodic
+   *   TRUE to enable periodic checks, FALSE otherwise.
+   *
+   * @return $this
+   */
+  public function setPeriodic(bool $periodic): FixityCheckInterface;
+
+  /**
+   * Gets the timestamp of when the check was queued.
+   *
+   * @return int
+   *   The timestamp when the check was queued.
+   *   0 indicates the check is not queued.
+   */
+  public function getQueued(): int;
+
+  /**
+   * Sets the timestamp of when the check was queued.
+   *
+   * @param int $queued
+   *   The timestamp when queued.
+   *
+   * @return $this
+   */
+  public function setQueued(int $queued): FixityCheckInterface;
+
+}

src/FixityCheckListBuilder.php

@@ -0,0 +1,123 @@
+<?php
+
+namespace Drupal\dgi_fixity;
+
+use Drupal\Core\Datetime\DateFormatterInterface;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\EntityListBuilder;
+use Drupal\Core\Entity\EntityStorageInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Render\RendererInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides a listing of fixity check items.
+ */
+class FixityCheckListBuilder extends EntityListBuilder {
+
+  /**
+   * The date formatter service.
+   *
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
+   */
+  protected $dateFormatter;
+
+  /**
+   * The renderer service.
+   *
+   * @var \Drupal\Core\Render\RendererInterface
+   */
+  protected $renderer;
+
+  /**
+   * Constructs a new FixityCheckListBuilder object.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type definition.
+   * @param \Drupal\Core\Entity\EntityStorageInterface $storage
+   *   The entity storage class.
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
+   *   The date formatter service.
+   * @param \Drupal\Core\Render\RendererInterface $renderer
+   *   The renderer service.
+   */
+  public function __construct(EntityTypeInterface $entity_type, EntityStorageInterface $storage, DateFormatterInterface $date_formatter, RendererInterface $renderer) {
+    parent::__construct($entity_type, $storage);
+    $this->dateFormatter = $date_formatter;
+    $this->renderer = $renderer;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function createInstance(ContainerInterface $container, EntityTypeInterface $entity_type) {
+    $entity_type_manager = $container->get('entity_type.manager');
+    return new static(
+      $entity_type,
+      $entity_type_manager->getStorage($entity_type->id()),
+      $container->get('date.formatter'),
+      $container->get('renderer'),
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildHeader() {
+    $header = [];
+    $header += [
+      'link' => [
+        'data' => $this->t('Check'),
+      ],
+      'state' => [
+        'data' => $this->t('State'),
+      ],
+      'performed' => [
+        'data' => $this->t('Performed'),
+      ],
+    ];
+    return $header + parent::buildHeader();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildRow(EntityInterface $entity) {
+    /** @var \Drupal\dgi_fixity\FixityCheckInterface $entity */
+    $row = [
+      'link' => $entity->toLink(),
+    ];
+
+    $row['state']['data'] = $entity->state->view([
+      'label' => 'hidden',
+      'type' => 'dgi_fixity_state',
+    ]);
+
+    // Use timestamp rather than timestamp_ago to allow for caching.
+    $row['performed']['data'] = $entity->wasPerformed() ?
+      $entity->performed->view([
+        'label' => 'hidden',
+        'type' => 'timestamp',
+        'weight' => 1,
+      ]) :
+      ['#markup' => $this->t('never')];
+
+    return $row + parent::buildRow($entity);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getEntityIds() {
+    $query = $this->getStorage()->getQuery()
+      ->accessCheck(TRUE)
+      ->sort('performed', 'DESC');
+
+    // Only add the pager if a limit is specified.
+    if ($this->limit) {
+      $query->pager($this->limit);
+    }
+    return $query->execute();
+  }
+
+}

src/FixityCheckService.php

@@ -0,0 +1,390 @@
+<?php
+
+namespace Drupal\dgi_fixity;
+
+use Drupal\Component\Datetime\TimeInterface;
+use Drupal\Core\Config\ConfigFactoryInterface;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Link;
+use Drupal\Core\Mail\MailManagerInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\Core\StringTranslation\TranslationInterface;
+use Drupal\dgi_fixity\Entity\FixityCheck;
+use Drupal\dgi_fixity\Form\SettingsForm;
+use Drupal\file\Entity\File;
+use Drupal\file\FileInterface;
+use Drupal\filehash\FileHash;
+use Drupal\media\MediaInterface;
+use Drupal\views\ViewExecutable;
+use Drupal\views\Views;
+use Psr\Log\LoggerInterface;
+
+/**
+ * Decorates the FileHash services adding additional functionality.
+ */
+class FixityCheckService implements FixityCheckServiceInterface {
+
+  use StringTranslationTrait;
+
+  /**
+   * Config factory.
+   *
+   * @var \Drupal\Core\Config\ConfigFactoryInterface
+   */
+  protected $config;
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * A date time instance.
+   *
+   * @var \Drupal\Component\Datetime\TimeInterface
+   */
+  protected $time;
+
+  /**
+   * The mail manager service.
+   *
+   * @var \Drupal\Core\Mail\MailManagerInterface
+   */
+  protected $mailManager;
+
+  /**
+   * The logger for this service.
+   *
+   * @var Psr\Log\LoggerInterface
+   */
+  protected $logger;
+
+  /**
+   * The service to decorate.
+   *
+   * @var \Drupal\filehash\FileHash
+   */
+  protected $filehash;
+
+  /**
+   * Constructor.
+   */
+  public function __construct(TranslationInterface $string_translation, ConfigFactoryInterface $config, EntityTypeManagerInterface $entity_type_manager, TimeInterface $time, MailManagerInterface $mail_manager, LoggerInterface $logger, FileHash $filehash) {
+    $this->stringTranslation = $string_translation;
+    $this->config = $config;
+    $this->entityTypeManager = $entity_type_manager;
+    $this->time = $time;
+    $this->mailManager = $mail_manager;
+    $this->logger = $logger;
+    $this->filehash = $filehash;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function fromEntityTypes(): array {
+    return [
+      'media',
+      'file',
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function fromEntity(EntityInterface $entity): ?FixityCheckInterface {
+    $entity_type_id = $entity->getEntityTypeId();
+    switch ($entity_type_id) {
+      case 'media':
+        /** @var \Drupal\media\MediaInterface $entity */
+        return $this->fromMedia($entity);
+
+      case 'file':
+        /** @var \Drupal\file\FileInterface $entity */
+        return $this->fromFile($entity);
+
+      default:
+        throw new \InvalidArgumentException("Cannot convert {$entity_type_id} to fixity_check.");
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function fromFile($file): ?FixityCheckInterface {
+    $fid = $file instanceof FileInterface ? $file->id() : (int) $file;
+    // It is only possible to have a single fixity_check entity per-file.
+    $results = $this->entityTypeManager->getStorage('fixity_check')->loadByProperties(['file' => $fid]);
+    if (count($results) === 1) {
+      /** @var \Drupal\dgi_fixity\FixityCheckInterface $fixity_check */
+      $fixity_check = reset($results);
+    }
+    else {
+      $fixity_check = FixityCheck::create([
+        'file' => $fid,
+      ]);
+    }
+    return $fixity_check;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function fromMedia(MediaInterface $media): ?FixityCheckInterface {
+    $fid = $media->getSource()->getSourceFieldValue($media);
+    return $this->fromFile($fid);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function threshold(): int {
+    $threshold = &drupal_static(__FUNCTION__);
+    if (is_null($threshold)) {
+      $settings = $this->config->get(SettingsForm::CONFIG_NAME);
+      $threshold = strtotime($settings->get(SettingsForm::THRESHOLD), $this->time->getRequestTime());
+    }
+    return $threshold;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function scheduled(FixityCheckInterface $check): ?int {
+    if ($check->getPeriodic()) {
+      $now = time();
+      if ($check->wasPerformed()) {
+        $diff = $now - $this->threshold();
+        return $check->getPerformed() + $diff;
+      }
+      // Never performed, can be performed immediately.
+      return $now;
+    }
+    // Not periodic therefore not scheduled.
+    return NULL;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function source(string $source, int $limit): ?ViewExecutable {
+    // Only process those which have not already enabled periodic checks.
+    [$view_id, $display_id] = explode(':', $source);
+    $view = Views::getView($view_id);
+    if ($view) {
+      $view->setDisplay($display_id);
+      $view->getDisplay()->setOption('entity_reference_options', ['limit' => $limit]);
+      $view->addHandler($display_id, 'relationship', 'file_managed', 'reverse_file_fixity_check');
+      $view->addHandler(
+        $display_id, 'filter', 'fixity_check', 'periodic',
+        ['relationship' => 'reverse_file_fixity_check', 'value' => 0],
+        'periodic'
+      );
+      $view->addHandler(
+        $display_id, 'field', 'fixity_check', 'periodic',
+        ['relationship' => 'reverse_file_fixity_check'],
+      'periodic'
+      );
+    }
+    return $view;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function check(File $file, bool $force = FALSE) {
+    /** @var \Drupal\dgi_fixity\Entity\FixityCheckInterface[] $existing_checks */
+    $existing_checks = $this->entityTypeManager->getStorage('fixity_check')->loadByProperties(['file' => $file->id()]);
+    if (empty($existing_checks)) {
+      $check = FixityCheck::create()->setFile($file);
+    }
+    else {
+      // Should only ever be at most one due to the UniqueFieldEntityReference
+      // constraint on the file field.
+      $check = reset($existing_checks);
+      // Do not perform if the threshold for time since the last check has not
+      // been exceeded.
+      if (!$force) {
+        if ($check->getPerformed() > $this->threshold()) {
+          return NULL;
+        }
+      }
+      // Trigger a new revision (clears the performed / state fields).
+      // If the check has never been performed before do not modify the
+      // existing version.
+      if ($check->wasPerformed()) {
+        $check->setNewRevision();
+      }
+    }
+    $uri = $file->getFileUri();
+    // Assume success until proven untrue.
+    $state = FixityCheck::STATE_MATCHES;
+    // If column is set, only generate that hash.
+    foreach ($this->filehash->algos() as $column => $algo) {
+      // Nothing to do if the previous checksum value is not known.
+      if (!isset($file->{$column})) {
+        $state = FixityCheck::STATE_NO_CHECKSUM;
+        break;
+      }
+      // Nothing to do if file URI is empty.
+      if (NULL === $uri || '' === $uri || !file_exists($uri)) {
+        $state = FixityCheck::STATE_MISSING;
+        break;
+      }
+      // Unreadable files will have NULL hash values.
+      elseif (preg_match('/^blake2b_([0-9]{3})$/', $algo, $matches)) {
+        $hash = $this->filehash->blake2b($uri, $matches[1] / 8) ?: NULL;
+      }
+      else {
+        $hash = hash_file($algo, $uri) ?: NULL;
+      }
+      if ($hash === NULL) {
+        $state = FixityCheck::STATE_GENERATION_FAILED;
+        break;
+      }
+      if ($file->{$column}->value !== $hash) {
+        $state = FixityCheck::STATE_MISMATCHES;
+        break;
+      }
+    }
+
+    $check->setState($state);
+    $check->setPerformed($this->time->getRequestTime());
+    $check->setQueued(0);
+    $check->save();
+
+    // Log results.
+    $message = '@entity-type %label: %state';
+    $args = [
+      '@entity-type' => $check->getEntityType()->getSingularLabel(),
+      '%label' => $check->label(),
+      '%state' => $check->getStateProperty($check->getState(), 'label'),
+      'link' => Link::createFromRoute(
+        $this->t('View'),
+        'entity.fixity_check.revision',
+        [
+          'fixity_check' => $check->id(),
+          'fixity_check_revision' => $check->getRevisionId(),
+        ],
+      )->toString(),
+    ];
+    if ($check->passed()) {
+      $this->logger->info($message, $args);
+    }
+    else {
+      $this->logger->error($message, $args);
+    }
+
+    return $check;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function stats(): array {
+    $storage = $this->entityTypeManager->getStorage('fixity_check');
+
+    // Group all current checks by their state.
+    // Ignore those that have not been performed yet.
+    $results = $storage->getAggregateQuery('AND')
+      ->condition('performed', 0, '!=')
+      ->groupBy('state')
+      ->aggregate('id', 'COUNT')
+      ->execute();
+
+    $failed = 0;
+    $states = [];
+    foreach ($results as $result) {
+      $state = $result['state'];
+      $count = $result['id_count'];
+      $states[$state] = $count;
+      // If there are any checks which have not 'passed', the aggregate state
+      // of all checks is failure.
+      if (FixityCheck::getStateProperty($state, 'passed') === FALSE) {
+        $failed += $count;
+      }
+    }
+
+    // All active checks.
+    $periodic = (int) $storage->getQuery('AND')
+      ->count('id')
+      ->condition('periodic', TRUE)
+      ->execute();
+
+    // All checks performed ever.
+    $revisions = (int) $storage->getQuery('AND')
+      ->allRevisions()
+      ->count('id')
+      ->execute();
+
+    // Checks which have exceeded the threshold and should be performed again.
+    $threshold = $this->threshold();
+    $current = (int) $storage->getQuery('AND')
+      ->condition('periodic', TRUE)
+      ->condition('performed', $threshold, '>=')
+      ->count('id')
+      ->execute();
+
+    // Up to date checks.
+    $expired = $periodic - $current;
+
+    return [
+      'periodic' => [
+        'total' => $periodic,
+        'current' => $current,
+        'expired' => $expired,
+      ],
+      'revisions' => $revisions,
+      'states' => $states,
+      'failed' => $failed,
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function summary(array $stats): array {
+    $summary = [];
+    $summary[] = $this->formatPlural(
+      $stats['revisions'],
+      '@count check has been performed since tracking started.',
+      '@count checks have been performed since tracking started.',
+    );
+    $summary[] = $this->formatPlural(
+      $stats['periodic']['total'],
+      '@count file is set to be checked periodically.',
+      '@count files are set to be checked periodically.',
+    );
+    $summary[] = $this->formatPlural(
+      $stats['periodic']['current'],
+      '@count periodic check is up to date.',
+      '@count periodic checks are up to date.',
+    );
+    if ($stats['periodic']['expired'] > 0) {
+      $summary[] = $this->formatPlural(
+        $stats['periodic']['expired'],
+        '@count periodic check is out to date.',
+        '@count periodic checks are out to date.',
+      );
+    }
+    if ($stats['failed'] > 0) {
+      $summary[] = $this->formatPlural(
+        $stats['failed'],
+        '@count check has failed.',
+        '@count checks have failed.',
+      );
+      foreach ($stats['states'] as $state => $count) {
+        $summary[] = $this->formatPlural(
+          $count,
+          FixityCheck::getStateProperty($state, 'singular'),
+          FixityCheck::getStateProperty($state, 'plural'),
+        );
+      }
+    }
+    return $summary;
+  }
+
+}

src/FixityCheckServiceInterface.php

@@ -0,0 +1,134 @@
+<?php
+
+namespace Drupal\dgi_fixity;
+
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\file\Entity\File;
+use Drupal\media\MediaInterface;
+use Drupal\views\ViewExecutable;
+
+/**
+ * Interface for FixityCheckService.
+ */
+interface FixityCheckServiceInterface {
+
+  /**
+   * A list of entity types which be converted into a fixity_check entity.
+   *
+   * @return string[]
+   *   A list of entity types which be converted into a fixity_check entity.
+   */
+  public function fromEntityTypes(): array;
+
+  /**
+   * Fetches or creates a fixity_check entity from the given media entity.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   A media entity.
+   *
+   * @return \Drupal\dgi_fixity\FixityCheckInterface
+   *   The fixity_check entity for the given entity if possible NULL otherwise.
+   */
+  public function fromEntity(EntityInterface $entity): ?FixityCheckInterface;
+
+  /**
+   * Fetches or creates a fixity_check entity from the given file entity.
+   *
+   * @param \Drupal\file\FileInterface|int $file
+   *   A file entity or file entity identifier.
+   *
+   * @return \Drupal\dgi_fixity\FixityCheckInterface
+   *   The fixity_check entity for the given file.
+   */
+  public function fromFile($file): ?FixityCheckInterface;
+
+  /**
+   * Fetches or creates a fixity_check entity from the given media entity.
+   *
+   * @param \Drupal\media\MediaInterface $media
+   *   A media entity.
+   *
+   * @return \Drupal\dgi_fixity\FixityCheckInterface
+   *   The fixity_check entity for the given media.
+   */
+  public function fromMedia(MediaInterface $media): ?FixityCheckInterface;
+
+  /**
+   * Gets the threshold for determining if checks should be performed.
+   *
+   * @return int
+   *   The timestamp for the threshold relative to the current request time.
+   */
+  public function threshold(): int;
+
+  /**
+   * Gets when the given check should be performed again.
+   *
+   * Only periodic checks can be scheduled.
+   *
+   * @return int|null
+   *   The timestamp when the check should be performed again if scheduled to,
+   *   NULL otherwise.
+   */
+  public function scheduled(FixityCheckInterface $check): ?int;
+
+  /**
+   * Gets the view for the given source, filtered to non-periodic files only.
+   *
+   * The source must comply with checks performed by this modules settings form.
+   * This function does not validate it.
+   *
+   * @param string $source
+   *   The view display identifier as selected in this modules settings form.
+   * @param int $limit
+   *   The maximum results the view should return.
+   *
+   * @return \Drupal\views\ViewExecutable|null
+   *   The filtered view.
+   */
+  public function source(string $source, int $limit): ?ViewExecutable;
+
+  /**
+   * Generates a fixity_check entity from the given file.
+   *
+   * Either adds a new revision or creates a new fixity_check.
+   *
+   * @param \Drupal\file\Entity\File $file
+   *   The file to perform the fixity check against.
+   * @param bool $force
+   *   A flag to indicate if the check should be performed even if the time
+   *   elapsed since the last check has not exceed the required threshold.
+   *
+   * @return \Drupal\dgi_fixity\Entity\FixityCheckInterface|null
+   *   The resulting fixity_check if successful.
+   *   NULL if the check was not performed because the time elapsed since the
+   *   last check has not exceed the required threshold.
+   */
+  public function check(File $file, bool $force = FALSE);
+
+  /**
+   * Get an associative array of statistics relating to FixityChecks.
+   *
+   * @return array
+   *   An associative array with the following fields:
+   *   - total: The number of active fixity checks.
+   *   - revisions: The total number of fixity checks ever performed.
+   *   - states: An associative array of states and their active counts.
+   *   - current: The number of checks that are up to date.
+   *   - expired: The number of checks that are out of date.
+   *   - failed: The number of checks in a failed state.
+   */
+  public function stats(): array;
+
+  /**
+   * Given stats provided by this service generate a summary.
+   *
+   * @param array $stats
+   *   The stats as returned by this service.
+   *
+   * @return \Drupal\Core\StringTranslation\TranslatableMarkup[]
+   *   A list of messages that describe the current state of the system.
+   */
+  public function summary(array $stats): array;
+
+}

src/FixityCheckStorage.php

@@ -0,0 +1,139 @@
+<?php
+
+namespace Drupal\dgi_fixity;
+
+use Drupal\Core\Entity\Sql\SqlContentEntityStorage;
+
+/**
+ * File storage for files.
+ */
+class FixityCheckStorage extends SqlContentEntityStorage implements FixityCheckStorageInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function countMissing(): int {
+    /** @var \Drupal\file\FileStorage $storage */
+    $storage = $this->entityTypeManager->getStorage('file');
+    $query = $this->database->select($storage->getBaseTable(), 'file_managed');
+    $query->leftJoin($this->baseTable, 'fixity_check', '[file_managed].[fid] = [fixity_check].[file]');
+    return $query
+      ->isNull('fixity_check.file')
+      ->countQuery()
+      ->execute()
+      ->fetchField();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getMissing(int $offset, int $limit): array {
+    /** @var \Drupal\file\FileStorage $storage */
+    $storage = $this->entityTypeManager->getStorage('file');
+    $query = $this->database->select($storage->getBaseTable(), 'file_managed');
+    $query->fields('file_managed', ['fid']);
+    $query->leftJoin($this->baseTable, 'fixity_check', '[file_managed].[fid] = [fixity_check].[file]');
+    $ids = $query
+      ->isNull('fixity_check.file')
+      ->orderBy('file_managed.fid')
+      ->range($offset, $limit)
+      ->execute()
+      ->fetchCol();
+    return $storage->loadMultiple($ids);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function clearPeriodic() {
+    $this->database
+      ->update($this->baseTable)
+      ->fields([
+        'periodic' => 0,
+      ])
+      ->execute();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function countPeriodic(): int {
+    return $this->database
+      ->select($this->baseTable, 'c')
+      ->condition('c.periodic', 1)
+      ->countQuery()
+      ->execute()
+      ->fetchField();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getPeriodic(int $offset, int $limit): array {
+    /** @var \Drupal\file\FileStorage $storage */
+    $storage = $this->entityTypeManager->getStorage('file');
+    $ids = $this->database
+      ->select($this->baseTable, 'c')
+      ->condition('c.periodic', 1)
+      ->fields('c', ['file'])
+      ->range($offset, $limit)
+      ->orderBy('id')
+      ->execute()
+      ->fetchCol();
+    return $storage->loadMultiple($ids);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function queue(int $queued, int $threshold, int $limit) {
+    // Do not over-saturate the queue.
+    // 10x the limit is the max we allow to be queued at a time.
+    $queue = \Drupal::queue('dgi_fixity.fixity_check');
+    if ($queue->numberOfItems() > (10 * $limit)) {
+      return;
+    }
+
+    $query = $this->database->select($this->baseTable, 'c');
+    // Either never performed or out of date.
+    $performed = $query->orConditionGroup()
+      ->condition('c.performed', 0, '=')
+      ->condition('c.performed', $threshold, '<=');
+
+    // Only those which have enabled periodic checking, and are not already
+    // queued.
+    $ids = $query
+      ->fields('c', ['id'])
+      ->condition('c.periodic', 1)
+      ->condition('c.queued', 0)
+      ->condition($performed)
+      ->range(0, $limit)
+      ->execute()
+      ->fetchCol();
+
+    /** @var \Drupal\dgi_fixity\FixityCheckInterface $check */
+    foreach ($this->doLoadMultiple($ids) as $check) {
+      // Queue checks for processing.
+      if ($queue->createItem($check)) {
+        // Add timestamp to avoid queueing item more than once.
+        $check->setQueued($queued);
+        $check->save();
+      }
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function dequeue(int $queued) {
+    $this->database
+      ->update($this->baseTable)
+      ->fields([
+        'queued' => 0,
+      ])
+      ->condition('queued', 0, '<>')
+      ->condition('queued', $queued, '<')
+      ->execute();
+  }
+
+}

src/FixityCheckStorageInterface.php

@@ -0,0 +1,79 @@
+<?php
+
+namespace Drupal\dgi_fixity;
+
+use Drupal\Core\Entity\ContentEntityStorageInterface;
+
+/**
+ * Defines an interface for fixity_check entity storage classes.
+ */
+interface FixityCheckStorageInterface extends ContentEntityStorageInterface {
+
+  /**
+   * Gets the number of files that have no related fixity_check entity.
+   *
+   * @return int
+   *   The number of files that have no related fixity_check entity.
+   */
+  public function countMissing(): int;
+
+  /**
+   * Gets a list of files which have no related fixity_check entity.
+   *
+   * @param int $offset
+   *   The offset into the list of files.
+   * @param int $limit
+   *   The maximum number of files to return.
+   *
+   * @return \Drupal\file\FileInterface[]
+   *   The files selected by the given parameters.
+   */
+  public function getMissing(int $offset, int $limit): array;
+
+  /**
+   * Gets the number of files that have enabled periodic checking.
+   *
+   * @return int
+   *   The number of files that have enabled periodic checking.
+   */
+  public function countPeriodic(): int;
+
+  /**
+   * Gets a list of files which have enabled periodic checking.
+   *
+   * @param int $offset
+   *   The offset into the list files.
+   * @param int $limit
+   *   The maximum number of files to return.
+   *
+   * @return \Drupal\file\FileInterface[]
+   *   The file selected by the given parameters.
+   */
+  public function getPeriodic(int $offset, int $limit): array;
+
+  /**
+   * Sets the periodic check flag on all files to FALSE.
+   */
+  public function clearPeriodic();
+
+  /**
+   * Queues checks to be performed during cron up to at most the given limit.
+   *
+   * @param int $queued
+   *   The timestamp newly queued items will be recorded under.
+   * @param int $threshold
+   *   Only queue checks which were performed before the given threshold.
+   * @param int $limit
+   *   The number of items to queue at most.
+   */
+  public function queue(int $queued, int $threshold, int $limit);
+
+  /**
+   * Dequeues checks which have not been performed before the given timestamp.
+   *
+   * @param int $queued
+   *   Items which were queued before this timestamp will be dequeued.
+   */
+  public function dequeue(int $queued);
+
+}

src/FixityCheckStorageSchema.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace Drupal\dgi_fixity;
+
+use Drupal\Core\Entity\Sql\SqlContentEntityStorageSchema;
+use Drupal\Core\Field\FieldStorageDefinitionInterface;
+
+/**
+ * Defines the file schema handler.
+ */
+class FixityCheckStorageSchema extends SqlContentEntityStorageSchema {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getSharedTableFieldSchema(FieldStorageDefinitionInterface $storage_definition, $table_name, array $column_mapping) {
+    $schema = parent::getSharedTableFieldSchema($storage_definition, $table_name, $column_mapping);
+    $field_name = $storage_definition->getName();
+
+    if ($table_name == $this->storage->getBaseTable()) {
+      switch ($field_name) {
+        case 'file':
+          $this->addSharedTableFieldUniqueKey($storage_definition, $schema, TRUE);
+          $this->addSharedTableFieldForeignKey($storage_definition, $schema, 'file_managed', 'fid');
+          break;
+
+        case 'state':
+        case 'performed':
+        case 'periodic':
+        case 'queued':
+          $this->addSharedTableFieldIndex($storage_definition, $schema, TRUE);
+          break;
+
+      }
+    }
+
+    return $schema;
+  }
+
+}

src/FixityCheckViewsData.php

@@ -0,0 +1,44 @@
+<?php
+
+namespace Drupal\dgi_fixity;
+
+use Drupal\views\EntityViewsData;
+
+/**
+ * Provides the views data for the fixity_check entity type.
+ */
+class FixityCheckViewsData extends EntityViewsData {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getViewsData() {
+    $data = parent::getViewsData();
+    $data['fixity_check']['table']['wizard_id'] = 'fixity_check';
+    $data['fixity_check']['table']['group'] = $this->t('Fixity Check');
+    $data['fixity_check']['table']['join'] = [
+      'fixity_check_revision' => [
+        'left_field' => 'revision_id',
+        'field' => 'revision_id',
+      ],
+      'file_managed' => [
+        'left_field' => 'fid',
+        'field' => 'file',
+      ],
+    ];
+    $data['fixity_check_revision']['table']['wizard_id'] = 'fixity_check_revision';
+    $data['fixity_check_revision']['table']['group'] = $this->t('Fixity Check revision');
+    $data['fixity_check_revision']['table']['join'] = [
+      'fixity_check' => [
+        'left_field' => 'revision_id',
+        'field' => 'revision_id',
+      ],
+      'file_managed' => [
+        'left_field' => 'fid',
+        'field' => 'file',
+      ],
+    ];
+    return $data;
+  }
+
+}

src/Form/BatchForm.php

@@ -0,0 +1,62 @@
+<?php
+
+namespace Drupal\dgi_fixity\Form;
+
+use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\dgi_fixity\FixityCheckBatchCheck;
+
+/**
+ * Trigger a batch check of the files selected by the modules configuration.
+ *
+ * @internal
+ */
+class BatchForm extends FormBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'dgi_fixity_batch_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    $form['info'] = [
+      '#type' => 'markup',
+      '#markup' => $this->t('Submitting this form will perform fixity checks against all files with periodic checks enabled.<br>This will automatically be done via cron, but it can be performed manually here.'),
+    ];
+    $form['force'] = [
+      '#type' => 'checkbox',
+      '#title' => $this->t('Skip time elapsed check'),
+      '#description' => $this->t('If enabled, all files will be checked without regard to the time elapsed since the previous check was performed on the selected file.'),
+      '#default' => FALSE,
+    ];
+    $form['actions'] = [
+      '#type' => 'actions',
+      'submit' => [
+        '#type' => 'submit',
+        '#value' => $this->t('Check'),
+        '#button_type' => 'primary',
+      ],
+    ];
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    $force = boolval($form_state->getValue('force'));
+    try {
+      $batch = FixityCheckBatchCheck::build(NULL, $force);
+      batch_set($batch);
+    }
+    catch (\InvalidArgumentException $e) {
+      $this->messenger()->addError($e->getMessage());
+    }
+  }
+
+}

src/Form/CheckForm.php

@@ -0,0 +1,160 @@
+<?php
+
+namespace Drupal\dgi_fixity\Form;
+
+use Drupal\Component\Datetime\TimeInterface;
+use Drupal\Core\Entity\ContentEntityConfirmFormBase;
+use Drupal\Core\Entity\EntityRepositoryInterface;
+use Drupal\Core\Entity\EntityTypeBundleInfoInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\dgi_fixity\FixityCheckInterface;
+use Drupal\dgi_fixity\FixityCheckServiceInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Perform a fixity check on the given fixity_check or related entity.
+ *
+ * @internal
+ */
+class CheckForm extends ContentEntityConfirmFormBase {
+
+  /**
+   * The fixity service.
+   *
+   * @var \Drupal\dgi_fixity\FixityCheckServiceInterface
+   */
+  protected $fixity;
+
+  /**
+   * The entity used to derive the fixity_check entity.
+   *
+   * @var \Drupal\Core\Entity\ContentEntityInterface
+   */
+  protected $sourceEntity;
+
+  /**
+   * Constructs the form.
+   *
+   * @param \Drupal\Core\Entity\EntityRepositoryInterface $entity_repository
+   *   The entity repository service.
+   * @param \Drupal\Core\Entity\EntityTypeBundleInfoInterface $entity_type_bundle_info
+   *   The entity type bundle service.
+   * @param \Drupal\Component\Datetime\TimeInterface $time
+   *   The time service.
+   * @param \Drupal\dgi_fixity\FixityCheckServiceInterface $fixity
+   *   The fixity service.
+   */
+  public function __construct(EntityRepositoryInterface $entity_repository, EntityTypeBundleInfoInterface $entity_type_bundle_info, TimeInterface $time, FixityCheckServiceInterface $fixity) {
+    parent::__construct($entity_repository, $entity_type_bundle_info, $time);
+    $this->fixity = $fixity;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('entity.repository'),
+      $container->get('entity_type.bundle.info'),
+      $container->get('datetime.time'),
+      $container->get('dgi_fixity.fixity_check')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getEntityFromRouteMatch(RouteMatchInterface $route_match, $entity_type_id) {
+    // Support checking entity types from which we can determine the associated
+    // fixity_check.
+    $entity = parent::getEntityFromRouteMatch($route_match, $entity_type_id);
+    // Allow the original to affect the redirect url. For example return to the
+    // media's audit page rather than the fixity_check's audit page.
+    $this->sourceEntity = $entity;
+    return ($entity instanceof FixityCheckInterface) ?
+      $entity :
+      $this->fixity->fromEntity($entity);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDescription() {
+    /** @var \Drupal\dgi_fixity\FixityCheckInterface $entity */
+    $entity = $this->getEntity();
+    if ($entity->wasPerformed()) {
+      $scheduled = $this->fixity->scheduled($entity);
+      if ($scheduled) {
+        return $this->t('
+          <strong>Latest Result:</strong> %state<br/>
+          <strong>Last Performed:</strong> %performed<br/>
+          <strong>Next Scheduled:</strong> %scheduled
+        ', [
+          '%state' => $entity->getStateLabel(),
+          '%performed' => date(DATE_RFC7231, $entity->getPerformed()),
+          '%scheduled' => date(DATE_RFC7231, $scheduled),
+        ]);
+      }
+      return $this->t('
+        <strong>Latest Result:</strong> %state<br/>
+        <strong>Last Performed:</strong> %performed
+      ', [
+        '%state' => $entity->getStateLabel(),
+        '%performed' => date(DATE_RFC7231, $entity->getPerformed()),
+        '%scheduled' => date(DATE_RFC7231, $scheduled),
+      ]);
+    }
+    return $this->t('No prior check has been performed.');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getQuestion() {
+    /** @var \Drupal\dgi_fixity\FixityCheckInterface $entity */
+    $entity = $this->getEntity();
+    return $this->t('Are you sure you want to perform a check on %label?', [
+      '%label' => $this->getEntity()->label(),
+      '%performed' => date(DATE_RFC7231, $entity->getPerformed()),
+    ]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCancelUrl() {
+    return $this->sourceEntity->toUrl('fixity-audit');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    parent::submitForm($form, $form_state);
+
+    /** @var \Drupal\dgi_fixity\FixityCheckInterface $entity */
+    $entity = $this->getEntity();
+    /** @var \Drupal\dgi_fixity\FixityCheckInterface $check */
+    $check = $this->fixity->check($entity->getFile(), TRUE);
+    $this->setEntity($check);
+    unset($entity);
+
+    $message = $this->t('The @entity-type %label: %state.', [
+      '@entity-type' => $check->getEntityType()->getSingularLabel(),
+      '%label' => $check->toLink()->toString(),
+      '%state' => $check->getStateLabel(),
+    ]);
+
+    if ($check->passed()) {
+      $this->messenger()->addStatus($message);
+    }
+    else {
+      $this->messenger()->addError($message);
+    }
+
+    // If no destination set return to the fixity check audit page.
+    $form_state->setRedirectUrl($this->getCancelUrl());
+  }
+
+}

src/Form/GenerateForm.php

@@ -0,0 +1,85 @@
+<?php
+
+namespace Drupal\dgi_fixity\Form;
+
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\dgi_fixity\FixityCheckBatchGenerate;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Generates a fixity check entity for all previously existing files.
+ *
+ * @internal
+ */
+class GenerateForm extends FormBase {
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * Constructs the form.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager.
+   */
+  public function __construct(EntityTypeManagerInterface $entity_type_manager) {
+    $this->entityTypeManager = $entity_type_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('entity_type.manager'),
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'dgi_fixity_generate_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    /** @var \Drupal\dgi_fixity\FixityCheckStorageInterface $storage */
+    $storage = $this->entityTypeManager->getStorage('fixity_check');
+    $form['info'] = [
+      '#type' => 'markup',
+      '#markup' => $this->t('
+          <p>Submitting this form generate fixity checks for @count files.</p>
+          <p>Generally this should only be required when the module is first installed.</p>
+        ',
+        ['@count' => $storage->countMissing()]
+      ),
+    ];
+    $form['actions'] = [
+      '#type' => 'actions',
+      'submit' => [
+        '#type' => 'submit',
+        '#value' => $this->t('Generate'),
+        '#button_type' => 'primary',
+      ],
+    ];
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    $batch = FixityCheckBatchGenerate::build();
+    batch_set($batch);
+  }
+
+}

src/Form/RevisionDeleteForm.php

@@ -0,0 +1,131 @@
+<?php
+
+namespace Drupal\dgi_fixity\Form;
+
+use Drupal\Core\Datetime\DateFormatterInterface;
+use Drupal\Core\Entity\RevisionableStorageInterface;
+use Drupal\Core\Form\ConfirmFormBase;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Url;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Delete a fixity_check revision.
+ *
+ * @internal
+ */
+class RevisionDeleteForm extends ConfirmFormBase {
+
+  /**
+   * The fixity_check revision to delete.
+   *
+   * @var \Drupal\dgi_fixity\FixityCheckInterface
+   */
+  protected $revision;
+
+  /**
+   * Entity revision storage.
+   *
+   * @var \Drupal\Core\Entity\RevisionableStorageInterface
+   */
+  protected $storage;
+
+  /**
+   * The date formatter service.
+   *
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
+   */
+  protected $dateFormatter;
+
+  /**
+   * Constructs the form.
+   *
+   * @param \Drupal\Core\Entity\RevisionableStorageInterface $storage
+   *   The revisionable storage.
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
+   *   The date formatter service.
+   */
+  public function __construct(RevisionableStorageInterface $storage, DateFormatterInterface $date_formatter) {
+    $this->storage = $storage;
+    $this->dateFormatter = $date_formatter;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('entity_type.manager')->getStorage('fixity_check'),
+      $container->get('date.formatter')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'dgi_fixity_revision_delete_confirm';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getQuestion() {
+    return $this->t('Are you sure you want to delete the revision from %revision-date?', [
+      '%revision-date' => $this->dateFormatter->format(
+        $this->revision->getPerformed()
+      ),
+    ]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCancelUrl() {
+    return new Url('entity.fixity_check.fixity_audit', [
+      'fixity_check' => $this->revision->id(),
+    ]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getConfirmText() {
+    return $this->t('Delete');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state, $fixity_check_revision = NULL) {
+    $this->revision = $this->storage->loadRevision($fixity_check_revision);
+    $form = parent::buildForm($form, $form_state);
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    $this->storage->deleteRevision($this->revision->getRevisionId());
+
+    $this->logger('content')->notice('Fixity Check: deleted %title revision %revision.', [
+      '%title' => $this->revision->label(),
+      '%revision' => $this->revision->getRevisionId(),
+    ]);
+    $this->messenger()->addStatus(
+      $this->t('Revision from %revision-date of %title has been deleted.',
+      [
+        '%revision-date' => $this->dateFormatter->format(
+          $this->revision->getPerformed()
+        ),
+        '%title' => $this->revision->label(),
+      ]
+    ));
+    $form_state->setRedirect('entity.fixity_check.fixity_audit', [
+      'fixity_check' => $this->revision->id(),
+    ]);
+  }
+
+}

src/Form/SettingsForm.php

@@ -0,0 +1,305 @@
+<?php
+
+namespace Drupal\dgi_fixity\Form;
+
+use Drupal\Component\Utility\Tags;
+use Drupal\Core\Config\ConfigFactoryInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Form\ConfigFormBase;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\State\StateInterface;
+use Drupal\views\Views;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Configure this module.
+ *
+ * @internal
+ */
+class SettingsForm extends ConfigFormBase {
+
+  const CONFIG_NAME = 'dgi_fixity.settings';
+  const SOURCES = 'sources';
+  const THRESHOLD = 'threshold';
+  const BATCH_SIZE = 'batch_size';
+  const NOTIFY_STATUS = 'notify_status';
+  const NOTIFY_USER = 'notify_user';
+  const NOTIFY_USER_THRESHOLD = 'notify_user_threshold';
+
+  const NOTIFY_STATUS_NEVER = 0;
+  const NOTIFY_STATUS_ALWAYS = 1;
+  const NOTIFY_STATUS_ERROR = 2;
+
+  // This is not stored as a configuration value but as a state value
+  // Though we allow the user to view it and reset it via this form.
+  const STATE_LAST_NOTIFICATION = 'dgi_fixity.last_notification';
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * The state manager.
+   *
+   * @var \Drupal\Core\State\StateInterface
+   */
+  protected $state;
+
+  /**
+   * Constructs a \Drupal\system\ConfigFormBase object.
+   *
+   * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
+   *   The factory for configuration objects.
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   Manages entity type plugin definitions.
+   * @param \Drupal\Core\State\StateInterface $state
+   *   State manager.
+   */
+  public function __construct(ConfigFactoryInterface $config_factory, EntityTypeManagerInterface $entity_type_manager, StateInterface $state) {
+    parent::__construct($config_factory);
+    $this->entityTypeManager = $entity_type_manager;
+    $this->state = $state;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+        $container->get('config.factory'),
+        $container->get('entity_type.manager'),
+        $container->get('state'),
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'dgi_fixity_settings_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getEditableConfigNames() {
+    return [
+      static::CONFIG_NAME,
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    $config = $this->config(static::CONFIG_NAME);
+    $displays = Views::getApplicableViews('entity_reference_display');
+    $view_storage = $this->entityTypeManager->getStorage('view');
+    $sources = [];
+    foreach ($displays as $data) {
+      [$view_id, $display_id] = $data;
+      /** @var \Drupal\views\Entity\View $view */
+      $view = $view_storage->load($view_id);
+      $tag = $view->getExecutable()->storage->get('tag');
+      // Only list views tagged with 'fixity'.
+      if (in_array('fixity', Tags::explode($tag))) {
+        $entity_type = $view->getExecutable()->getBaseEntityType();
+        // Only use views that return 'file' entities, as the batch and workers
+        // dynamically filter the view by relating it to 'fixity_checks' that
+        // do not yet have their 'periodic' flag set to TRUE.
+        if ($entity_type && $entity_type->id() == 'file') {
+          $display = $view->get('display');
+          $set_name = $view_id . ':' . $display_id;
+          $sources[$set_name] = $display[$display_id]['display_title'] . ' (' . $set_name . ')';
+        }
+      }
+    }
+
+    $form['checks'] = [
+      '#type' => 'details',
+      '#title' => $this->t('Fixity Checks'),
+      '#open' => TRUE,
+      static::SOURCES => [
+        '#title' => $this->t('File Selection'),
+        '#description' => $this->t('
+          <p>Select one or more <strong>Views</strong>. Whose results are used to determine which files have periodic checks enabled according to the schedule below.</p>
+          <p>Only <em>File Entity</em> <strong>Views</strong> are supported.</p>
+          <p>Only <strong>entity_reference</strong> or <strong>entity_reference_revisions</strong> displays are supported.</p>
+          <p>If selecting multiple Views ideally they should not overlap, if only for the sake of efficiency.</p>
+          <p>Views must be have an administrative tag <strong>fixity</strong> to appear in this list.</p>
+        '),
+        '#type' => 'checkboxes',
+        '#options' => $sources,
+        '#default_value' => $config->get(static::SOURCES) ?: [],
+      ],
+      static::THRESHOLD => [
+        '#type' => 'textfield',
+        '#required' => TRUE,
+        '#title' => $this->t('Time elapsed'),
+        '#description' => $this->t('
+          <p>Time threshold is relative to "<em>now</em>". For example "<em>-1 month</em>" would prevent any checks that occurred less than a month ago.</p>
+          <p>Check <a href="https://www.php.net/manual/en/datetime.formats.relative.php">Relative Formats</a> for acceptable values</p>
+        '),
+        '#default_value' => $config->get(static::THRESHOLD) ?: '-1 month',
+        '#element_validate' => [
+          [$this, 'validateThreshold'],
+        ],
+      ],
+      static::BATCH_SIZE => [
+        '#type' => 'number',
+        '#required' => TRUE,
+        '#title' => $this->t('Batch size'),
+        '#description' => $this->t('
+          <p>Set how many files will be processed at once when performing a batch / cron job</p>
+        '),
+        '#default_value' => 100,
+      ],
+    ];
+
+    // Default to the admin user if not given.
+    $user = $config->get(static::NOTIFY_USER);
+    $user = is_int($user) ?
+      $this->entityTypeManager->getStorage('user')->load($user) :
+      $this->entityTypeManager->getStorage('user')->load(1);
+
+    $notification_threshold = $config->get(static::NOTIFY_USER_THRESHOLD) ?: '-1 week';
+    $last_notification = $this->state->get(static::STATE_LAST_NOTIFICATION);
+    if ($last_notification !== NULL) {
+      $next_notification = $last_notification + (time() - strtotime($notification_threshold));
+    }
+
+    $form['notify'] = [
+      '#type' => 'details',
+      '#title' => $this->t('Notifications'),
+      '#description' => $this->t('Notifications are sent by email to the selected user.'),
+      '#open' => TRUE,
+      static::NOTIFY_STATUS => [
+        '#type' => 'select',
+        '#title' => $this->t('Notification Status'),
+        '#description' => $this->t('
+          <p>Choose under what conditions should notifications be sent to the selected user.</p>
+        '),
+        '#options' => [
+          static::NOTIFY_STATUS_NEVER => $this->t('Never'),
+          static::NOTIFY_STATUS_ALWAYS => $this->t('Always'),
+          static::NOTIFY_STATUS_ERROR => $this->t('Only if error'),
+        ],
+        '#default_value' => $config->get(static::NOTIFY_STATUS) ?? static::NOTIFY_STATUS_ERROR,
+      ],
+      static::NOTIFY_USER => [
+        '#type' => 'entity_autocomplete',
+        '#required' => TRUE,
+        '#title' => $this->t('User'),
+        '#description' => $this->t('
+          <p>The user to be notified should one or more fixity checks fail.</p>
+          <p>The user will be notified by email.</p>
+        '),
+        '#target_type' => 'user',
+        '#default_value' => $user,
+        '#selection_settings' => [
+          'include_anonymous' => FALSE,
+        ],
+      ],
+      static::NOTIFY_USER_THRESHOLD => [
+        '#type' => 'textfield',
+        '#required' => TRUE,
+        '#title' => $this->t('Time elapsed'),
+        '#description' => $this->t('
+          <p>Time threshold is relative to "<em>now</em>". For example "<em>-1 week</em>" would mean a week must pass between notifications.</p>
+          <p>Check <a href="https://www.php.net/manual/en/datetime.formats.relative.php">Relative Formats</a> for acceptable values</p>
+        '),
+        '#default_value' => $notification_threshold,
+        '#element_validate' => [
+          [$this, 'validateThreshold'],
+        ],
+      ],
+      'last' => $last_notification ?
+        [
+          '#type' => 'details',
+          '#title' => $this->t('Last notification'),
+          '#description' => $this->t('
+            <p>The last notification was sent on %last.</p>
+            <p>At earliest the next message can be sent %next.</p>
+            ', [
+              '%last' => date(DATE_RFC7231, $last_notification),
+              '%next' => date(DATE_RFC7231, $next_notification),
+            ]
+          ),
+          static::STATE_LAST_NOTIFICATION => [
+            '#type' => 'button',
+            '#value' => $this->t('Reset'),
+            '#limit_validation_errors' => [],
+            '#executes_submit_callback' => TRUE,
+            '#submit' => [
+              [$this, 'resetLastNotification'],
+            ],
+          ],
+        ] : NULL,
+    ];
+
+    return parent::buildForm($form, $form_state);
+  }
+
+  /**
+   * Element validate callback; validate the threshold is valid.
+   */
+  public function validateThreshold(array $element, FormStateInterface $form_state, array $form) {
+    $value = $form_state->getValue($element['#parents']);
+    if (strtotime($value) === FALSE) {
+      $form_state->setError($element, $this->t('The given threshold is not valid.'));
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    $value = $form_state->getValue(static::NOTIFY_USER);
+    /** @var \Drupal\user\Entity\User $user */
+    $user = is_numeric($value) ?
+      $this->entityTypeManager->getStorage('user')->load($value) :
+      NULL;
+    if ($user === NULL) {
+      // Just a precaution the default form element validation should
+      // catch this case anyways.
+      $form_state->setError($form['notify'][static::NOTIFY_USER], $this->t('The given user does not exist.'));
+    }
+    elseif ($user->getEmail() === NULL) {
+      $form_state->setError($form['notify'][static::NOTIFY_USER], $this->t('The given user does <em>not</em> have an email address associated with their account.'));
+    }
+  }
+
+  /**
+   * Resets the stored last notification.
+   *
+   * @param array $form
+   *   An associative array containing the structure of the form.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The current state of the form.
+   */
+  public function resetLastNotification(array &$form, FormStateInterface $form_state) {
+    $this->state->delete(static::STATE_LAST_NOTIFICATION);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    $values = $form_state->getValues();
+    $config = $this->config(static::CONFIG_NAME);
+    $sources = array_keys(array_filter($values[static::SOURCES]));
+    $config
+      ->set(static::SOURCES, array_combine($sources, $sources))
+      ->set(static::THRESHOLD, $values[static::THRESHOLD])
+      ->set(static::BATCH_SIZE, $values[static::BATCH_SIZE])
+      ->set(static::NOTIFY_STATUS, $values[static::NOTIFY_STATUS])
+      ->set(static::NOTIFY_USER, $values[static::NOTIFY_USER])
+      ->set(static::NOTIFY_USER_THRESHOLD, $values[static::NOTIFY_USER_THRESHOLD])
+      ->save();
+    parent::submitForm($form, $form_state);
+  }
+
+}

src/Plugin/Action/CheckAction.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace Drupal\dgi_fixity\Plugin\Action;
+
+/**
+ * Performs a fixity checks on the entity.
+ *
+ * @Action(
+ *   id = "dgi_fixity:check_action",
+ *   action_label = @Translation("Check"),
+ *   deriver = "Drupal\dgi_fixity\Plugin\Action\Derivative\FixityCheckActionDeriver",
+ * )
+ */
+class CheckAction extends FixityCheckActionBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function execute($entity = NULL) {
+    $check = $this->getCheck($entity);
+    if ($check) {
+      $this->fixity->check($check->getFile(), TRUE);
+    }
+  }
+
+}

src/Plugin/Action/Derivative/FixityCheckActionDeriver.php

@@ -0,0 +1,62 @@
+<?php
+
+namespace Drupal\dgi_fixity\Plugin\Action\Derivative;
+
+use Drupal\Core\Action\Plugin\Action\Derivative\EntityActionDeriverBase;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\StringTranslation\TranslationInterface;
+use Drupal\dgi_fixity\FixityCheckServiceInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides an action deriver that finds publishable entity types.
+ *
+ * @see \Drupal\Core\Action\Plugin\Action\PublishAction
+ * @see \Drupal\Core\Action\Plugin\Action\UnpublishAction
+ */
+class FixityCheckActionDeriver extends EntityActionDeriverBase {
+
+  /**
+   * The fixity check service.
+   *
+   * @var \Drupal\dgi_fixity\FixityCheckServiceInterface
+   */
+  protected $fixity;
+
+  /**
+   * Constructs a new EntityActionDeriverBase object.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager.
+   * @param \Drupal\Core\StringTranslation\TranslationInterface $string_translation
+   *   The string translation service.
+   * @param \Drupal\dgi_fixity\FixityCheckServiceInterface $fixity
+   *   The fixity service.
+   */
+  public function __construct(EntityTypeManagerInterface $entity_type_manager, TranslationInterface $string_translation, FixityCheckServiceInterface $fixity) {
+    $this->entityTypeManager = $entity_type_manager;
+    $this->stringTranslation = $string_translation;
+    $this->fixity = $fixity;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, $base_plugin_id) {
+    return new static(
+      $container->get('entity_type.manager'),
+      $container->get('string_translation'),
+      $container->get('dgi_fixity.fixity_check'),
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function isApplicable(EntityTypeInterface $entity_type) {
+    $supported_entity_types = array_merge(['fixity_check'], $this->fixity->fromEntityTypes());
+    return in_array($entity_type->id(), $supported_entity_types);
+  }
+
+}

src/Plugin/Action/FixityCheckActionBase.php

@@ -0,0 +1,85 @@
+<?php
+
+namespace Drupal\dgi_fixity\Plugin\Action;
+
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Action\Plugin\Action\EntityActionBase;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Session\AccountInterface;
+use Drupal\dgi_fixity\FixityCheckInterface;
+use Drupal\dgi_fixity\FixityCheckServiceInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Base class for fixity_check entity-based actions.
+ */
+abstract class FixityCheckActionBase extends EntityActionBase {
+
+  /**
+   * The fixity check service.
+   *
+   * @var \Drupal\dgi_fixity\FixityCheckServiceInterface
+   */
+  protected $fixity;
+
+  /**
+   * Constructs a CheckAction object.
+   *
+   * @param array $configuration
+   *   A configuration array containing information about the plugin instance.
+   * @param string $plugin_id
+   *   The plugin_id for the plugin instance.
+   * @param mixed $plugin_definition
+   *   The plugin implementation definition.
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager.
+   * @param \Drupal\dgi_fixity\FixityCheckServiceInterface $fixity
+   *   The fixity service.
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, EntityTypeManagerInterface $entity_type_manager, FixityCheckServiceInterface $fixity) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition, $entity_type_manager);
+    $this->fixity = $fixity;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $container->get('entity_type.manager'),
+      $container->get('dgi_fixity.fixity_check'),
+    );
+  }
+
+  /**
+   * Gets the related fixity_check entity for the given entity if possible.
+   *
+   * @param \Drupal\Core\Entity\EntityInterface $entity
+   *   The related entity.
+   *
+   * @return \Drupal\dgi_fixity\FixityCheckInterface
+   *   The related fixity_check if found or NULL.
+   */
+  protected function getCheck(EntityInterface $entity): ?FixityCheckInterface {
+    return $entity instanceof FixityCheckInterface ?
+      $entity :
+      $this->fixity->fromEntity($entity);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function access($object, AccountInterface $account = NULL, $return_as_object = FALSE) {
+    // If it exists and the user has permission to administer fixity checks.
+    $result = $this->getCheck($object) && $account->hasPermission('administer fixity checks') ?
+      AccessResult::allowed() :
+      AccessResult::forbidden();
+
+    return $return_as_object ? $result : $result->isAllowed();
+  }
+
+}

src/Plugin/Action/PeriodicDisableAction.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace Drupal\dgi_fixity\Plugin\Action;
+
+/**
+ * Disables periodic checks on the the entity.
+ *
+ * @Action(
+ *   id = "dgi_fixity:periodic_disable_action",
+ *   action_label = @Translation("Disable periodic checks"),
+ *   deriver = "Drupal\dgi_fixity\Plugin\Action\Derivative\FixityCheckActionDeriver",
+ * )
+ */
+class PeriodicDisableAction extends FixityCheckActionBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function execute($entity = NULL) {
+    $check = $this->getCheck($entity);
+    if ($check) {
+      $check->setPeriodic(FALSE);
+      $check->save();
+    }
+  }
+
+}

src/Plugin/Action/PeriodicEnableAction.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace Drupal\dgi_fixity\Plugin\Action;
+
+/**
+ * Enable periodic checks on the the entity.
+ *
+ * @Action(
+ *   id = "dgi_fixity:periodic_enable_action",
+ *   action_label = @Translation("Enable periodic checks"),
+ *   deriver = "Drupal\dgi_fixity\Plugin\Action\Derivative\FixityCheckActionDeriver",
+ * )
+ */
+class PeriodicEnableAction extends FixityCheckActionBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function execute($entity = NULL) {
+    $check = $this->getCheck($entity);
+    if ($check) {
+      $check->setPeriodic(TRUE);
+      $check->save();
+    }
+  }
+
+}

src/Plugin/Derivative/FixityCheckLocalTasks.php

@@ -0,0 +1,80 @@
+<?php
+
+namespace Drupal\dgi_fixity\Plugin\Derivative;
+
+use Drupal\Component\Plugin\Derivative\DeriverBase;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Plugin\Discovery\ContainerDeriverInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\Core\StringTranslation\TranslationInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Generates fixity related local tasks.
+ */
+class FixityCheckLocalTasks extends DeriverBase implements ContainerDeriverInterface {
+
+  use StringTranslationTrait;
+
+  /**
+   * The entity manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * Creates a local tasks for fixity checks on supported entities.
+   *
+   * @param \Drupal\Core\StringTranslation\TranslationInterface $string_translation
+   *   The translation manager.
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity manager.
+   */
+  public function __construct(TranslationInterface $string_translation, EntityTypeManagerInterface $entity_type_manager) {
+    $this->stringTranslation = $string_translation;
+    $this->entityTypeManager = $entity_type_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, $base_plugin_id) {
+    return new static(
+      $container->get('string_translation'),
+      $container->get('entity_type.manager'),
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDerivativeDefinitions($base_plugin_definition) {
+    foreach ($this->entityTypeManager->getDefinitions() as $entity_type_id => $entity_type) {
+      if ($entity_type->hasLinkTemplate('fixity-audit')) {
+        $this->derivatives["$entity_type_id.fixity"] = [
+          'route_name' => "entity.{$entity_type_id}.fixity_audit",
+          'title' => $this->t('Fixity'),
+          'base_route' => "entity.{$entity_type_id}.canonical",
+          'weight' => 10,
+        ];
+        $this->derivatives["$entity_type_id.fixity.audit"] = [
+          'route_name' => "entity.$entity_type_id.fixity_audit",
+          'title' => $this->t('Audit'),
+          'parent_id' => "dgi_fixity.entities:$entity_type_id.fixity",
+          'weight' => 10,
+        ];
+        if ($entity_type->hasLinkTemplate('fixity-check')) {
+          $this->derivatives["$entity_type_id.fixity.check"] = [
+            'route_name' => "entity.$entity_type_id.fixity_check",
+            'title' => $this->t('Check'),
+            'parent_id' => "dgi_fixity.entities:$entity_type_id.fixity",
+            'weight' => 10,
+          ];
+        }
+      }
+    }
+    return $this->derivatives;
+  }
+
+}

src/Plugin/Field/FieldFormatter/FileReferenceFormatter.php

@@ -0,0 +1,47 @@
+<?php
+
+namespace Drupal\dgi_fixity\Plugin\Field\FieldFormatter;
+
+use Drupal\Core\Field\FieldItemListInterface;
+use Drupal\Core\Field\Plugin\Field\FieldFormatter\EntityReferenceFormatterBase;
+use Drupal\Core\Url;
+
+/**
+ * Formats file reference as a link to the file.
+ *
+ * @FieldFormatter(
+ *   id = "dgi_fixity_file_reference",
+ *   label = @Translation("Fixity File Reference"),
+ *   description = @Translation("Display a link to the file being referenced by a Fixity Check."),
+ *   field_types = {
+ *     "entity_reference"
+ *   }
+ * )
+ */
+class FileReferenceFormatter extends EntityReferenceFormatterBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function viewElements(FieldItemListInterface $items, $langcode) {
+    $elements = [];
+    /** @var \Drupal\file\Entity\File $entity */
+    foreach ($this->getEntitiesToView($items, $langcode) as $delta => $entity) {
+      $label = $entity->label();
+      $uri = $entity->createFileUrl(FALSE);
+      if (isset($uri)) {
+        $elements[$delta] = [
+          '#type' => 'link',
+          '#title' => $label,
+          '#url' => Url::fromUri($uri),
+        ];
+      }
+      else {
+        $elements[$delta] = ['#plain_text' => $label];
+      }
+      $elements[$delta]['#cache']['tags'] = $entity->getCacheTags();
+    }
+    return $elements;
+  }
+
+}

src/Plugin/Field/FieldFormatter/StateFormatter.php

@@ -0,0 +1,33 @@
+<?php
+
+namespace Drupal\dgi_fixity\Plugin\Field\FieldFormatter;
+
+use Drupal\Core\Field\FieldItemListInterface;
+use Drupal\Core\Field\FormatterBase;
+use Drupal\dgi_fixity\Entity\FixityCheck;
+
+/**
+ * Displays a human readable label for the state.
+ *
+ * @FieldFormatter(
+ *   id = "dgi_fixity_state",
+ *   label = @Translation("State"),
+ *   field_types = {
+ *     "integer"
+ *   },
+ * )
+ */
+class StateFormatter extends FormatterBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function viewElements(FieldItemListInterface $items, $langcode) {
+    $elements = [];
+    foreach ($items as $delta => $item) {
+      $elements[$delta] = ['#markup' => FixityCheck::getStateProperty($item->value, 'label')];
+    }
+    return $elements;
+  }
+
+}

src/Plugin/QueueWorker/FixityCheckWorker.php

@@ -0,0 +1,68 @@
+<?php
+
+namespace Drupal\dgi_fixity\Plugin\QueueWorker;
+
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\Core\Queue\QueueWorkerBase;
+use Drupal\dgi_fixity\FixityCheckServiceInterface;
+use Drupal\dgi_fixity\FixityCheckInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Performs a fixity check.
+ *
+ * @QueueWorker(
+ *   id = "dgi_fixity.fixity_check",
+ *   title = @Translation("Fixity Checks"),
+ *   cron = {"time" = 15}
+ * )
+ */
+class FixityCheckWorker extends QueueWorkerBase implements ContainerFactoryPluginInterface {
+
+  /**
+   * The fixity check service.
+   *
+   * @var \Drupal\dgi_fixity\FixityCheckServiceInterface
+   */
+  protected $fixity;
+
+  /**
+   * Constructs a new FixityCheckWorker instance.
+   *
+   * @param array $configuration
+   *   A configuration array containing information about the plugin instance.
+   * @param string $plugin_id
+   *   The plugin_id for the plugin instance.
+   * @param mixed $plugin_definition
+   *   The plugin implementation definition.
+   * @param \Drupal\dgi_fixity\FixityCheckServiceInterface $fixity
+   *   The fixity check service.
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, FixityCheckServiceInterface $fixity) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+    $this->fixity = $fixity;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $container->get('dgi_fixity.fixity_check'),
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function processItem($data) {
+    if ($data instanceof FixityCheckInterface) {
+      /** @var \Drupal\dgi_fixity\FixityCheckInterface $data */
+      $this->fixity->check($data->getFile());
+    }
+  }
+
+}

src/Plugin/QueueWorker/ProcessSourceWorker.php

@@ -0,0 +1,79 @@
+<?php
+
+namespace Drupal\dgi_fixity\Plugin\QueueWorker;
+
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\Core\Queue\QueueWorkerBase;
+use Drupal\Core\Queue\RequeueException;
+use Drupal\dgi_fixity\FixityCheckServiceInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Processes configured sources to find new files to periodically check.
+ *
+ * @QueueWorker(
+ *   id = "dgi_fixity.process_source",
+ *   title = @Translation("Fixity Check Process Source"),
+ *   cron = {"time" = 15}
+ * )
+ */
+class ProcessSourceWorker extends QueueWorkerBase implements ContainerFactoryPluginInterface {
+
+  /**
+   * The fixity check service.
+   *
+   * @var \Drupal\dgi_fixity\FixityCheckServiceInterface
+   */
+  protected $fixity;
+
+  /**
+   * Constructs a new FixityCheckWorker instance.
+   *
+   * @param array $configuration
+   *   A configuration array containing information about the plugin instance.
+   * @param string $plugin_id
+   *   The plugin_id for the plugin instance.
+   * @param mixed $plugin_definition
+   *   The plugin implementation definition.
+   * @param \Drupal\dgi_fixity\FixityCheckServiceInterface $fixity
+   *   The fixity check service.
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, FixityCheckServiceInterface $fixity) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+    $this->fixity = $fixity;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $container->get('dgi_fixity.fixity_check'),
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function processItem($data) {
+    /** @var \Drupal\dgi_fixity\FixityCheckServiceInterface $fixity */
+    $fixity = \Drupal::service('dgi_fixity.fixity_check');
+    $view = $fixity->source($data, 1000);
+    $view->execute();
+    // Only processes those which have not already enabled periodic checks.
+    foreach ($view->result as $row) {
+      /** @var \Drupal\dgi_fixity\FixityCheckInterface $check */
+      $check = $view->field['periodic']->getEntity($row);
+      $check->setPeriodic(TRUE);
+      $check->save();
+    }
+    // Not finished processing.
+    if (count($view->result) !== 0) {
+      throw new RequeueException();
+    }
+  }
+
+}

src/Plugin/Validation/Constraint/UniqueFieldEntityReferenceConstraint.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace Drupal\dgi_fixity\Plugin\Validation\Constraint;
+
+use Symfony\Component\Validator\Constraint;
+
+/**
+ * Checks if an entity field has a unique entity reference value.
+ *
+ * @Constraint(
+ *   id = "UniqueFieldEntityReference",
+ *   label = @Translation("Unique field entity reference constraint", context = "Validation"),
+ *   type = { "entity_reference" }
+ * )
+ */
+class UniqueFieldEntityReferenceConstraint extends Constraint {
+  /**
+   * The message to display to the user on invalid condition.
+   *
+   * @var string
+   */
+  public $message = 'The @referenced_entity_type: %entity_referenced is already a referenced by @entity_type: %entity';
+
+}

src/Plugin/Validation/Constraint/UniqueFieldEntityReferenceConstraintValidator.php

@@ -0,0 +1,67 @@
+<?php
+
+namespace Drupal\dgi_fixity\Plugin\Validation\Constraint;
+
+use Symfony\Component\Validator\Constraint;
+use Symfony\Component\Validator\ConstraintValidator;
+
+/**
+ * Validates the UniqueFieldEntityReferenceConstraint constraint.
+ */
+class UniqueFieldEntityReferenceConstraintValidator extends ConstraintValidator {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validate($items, Constraint $constraint) {
+    /** @var \Drupal\Core\Field\EntityReferenceFieldItemList $items */
+    /** @var UniqueFieldEntityReferenceConstraint $constraint */
+    /** @var \Drupal\Core\Field\EntityReferenceFieldItem $item */
+    if (!$item = $items->first()) {
+      return;
+    }
+    $target_property = $item->mainPropertyName();
+    $field_name = $items->getFieldDefinition()->getName();
+    /** @var \Drupal\Core\Entity\EntityInterface $entity */
+    $entity = $items->getEntity();
+    $entity_type_id = $entity->getEntityTypeId();
+    $id_key = $entity->getEntityType()->getKey('id');
+
+    $query = \Drupal::entityQuery($entity_type_id);
+    $query->accessCheck(FALSE);
+
+    $entity_id = $entity->id();
+    // Using isset() instead of !empty() as 0 and '0' are valid ID values for
+    // entity types using string IDs.
+    if (isset($entity_id)) {
+      $query->condition($id_key, $entity_id, '<>');
+    }
+    $targets = [];
+    foreach ($items as $item) {
+      $targets[] = $item->{$target_property};
+    }
+
+    $targets = array_filter($targets);
+    $results = $query
+      ->condition($field_name, $targets, 'IN')
+      ->range(0, 1)
+      ->execute();
+
+    if (count($results) > 0) {
+      $used_by_entity_id = reset($results);
+      $used_by_entity = \Drupal::entityTypeManager()->getStorage($entity_type_id)->load($used_by_entity_id);
+      foreach ($used_by_entity->{$field_name}->referencedEntities() as $reference) {
+        if (in_array($reference->id(), $targets)) {
+          $this->context->addViolation($constraint->message, [
+            '@referenced_entity_type' => $reference->getEntityTypeId(),
+            '%entity_referenced' => $reference->id(),
+            '@entity_type' => $entity_type_id,
+            '%entity' => $used_by_entity_id,
+          ]);
+          break;
+        }
+      }
+    }
+  }
+
+}

src/Plugin/views/wizard/FixityCheck.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace Drupal\dgi_fixity\Plugin\views\wizard;
+
+use Drupal\views\Plugin\views\wizard\WizardPluginBase;
+
+/**
+ * Used for creating 'fixity_check' views with the wizard.
+ *
+ * @ViewsWizard(
+ *   id = "fixity_check",
+ *   base_table = "fixity_check",
+ *   title = @Translation("Fixity Check"),
+ * )
+ */
+class FixityCheck extends WizardPluginBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $createdColumn = 'fixity_check-performed';
+
+}

src/Plugin/views/wizard/FixityCheckRevision.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace Drupal\dgi_fixity\Plugin\views\wizard;
+
+use Drupal\views\Plugin\views\wizard\WizardPluginBase;
+
+/**
+ * Used for creating 'fixity_check' views with the wizard.
+ *
+ * @ViewsWizard(
+ *   id = "fixity_check_revision",
+ *   base_table = "fixity_check_revision",
+ *   title = @Translation("Fixity Check Revision"),
+ * )
+ */
+class FixityCheckRevision extends WizardPluginBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $createdColumn = 'fixity_check_revision-performed';
+
+}

src/Routing/FixityCheckConverter.php

@@ -0,0 +1,65 @@
+<?php
+
+namespace Drupal\dgi_fixity\Routing;
+
+use Drupal\Core\Entity\EntityRepositoryInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\ParamConverter\EntityConverter;
+use Drupal\dgi_fixity\FixityCheckServiceInterface;
+use Symfony\Component\Routing\Route;
+
+/**
+ * Converts an entity identifier into fixity_check entity.
+ */
+class FixityCheckConverter extends EntityConverter {
+
+  /**
+   * The fixity service.
+   *
+   * @var \Drupal\dgi_fixity\FixityCheckServiceInterface
+   */
+  protected $fixity;
+
+  /**
+   * Construct a new FixityCheckConverter.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager.
+   * @param \Drupal\Core\Entity\EntityRepositoryInterface $entity_repository
+   *   The entity repository.
+   * @param \Drupal\dgi_fixity\FixityCheckServiceInterface $fixity
+   *   The fixity service.
+   */
+  public function __construct(EntityTypeManagerInterface $entity_type_manager, EntityRepositoryInterface $entity_repository, FixityCheckServiceInterface $fixity) {
+    parent::__construct($entity_type_manager, $entity_repository);
+    $this->fixity = $fixity;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function convert($value, $definition, $name, array $defaults) {
+    /** @var \Drupal\Core\Entity\EntityInterface $entity */
+    $entity = parent::convert($value, $definition, $name, $defaults);
+    return $this->fixity->fromEntity($entity);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function applies($definition, $name, Route $route) {
+    $supported_entity_types = $this->fixity->fromEntityTypes();
+    if (!empty($definition['type']) && strpos($definition['type'], 'fixity:') === 0) {
+      $entity_type_id = substr($definition['type'], strlen('fixity:'));
+      if (strpos($definition['type'], '{') !== FALSE) {
+        $entity_type_slug = substr($entity_type_id, 1, -1);
+        if ($name != $entity_type_slug && in_array($entity_type_slug, $route->compile()->getVariables(), TRUE)) {
+          return in_array($entity_type_slug, $supported_entity_types);
+        }
+      }
+      return in_array($entity_type_id, $supported_entity_types);
+    }
+    return FALSE;
+  }
+
+}

src/Routing/FixityCheckRouteProvider.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace Drupal\dgi_fixity\Routing;
+
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Entity\Routing\AdminHtmlRouteProvider;
+
+/**
+ * Sets defaults on HTML routes for the fixity_check entity.
+ *
+ * @see \Drupal\Core\Entity\Routing\AdminHtmlRouteProvider.
+ */
+class FixityCheckRouteProvider extends AdminHtmlRouteProvider {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getCanonicalRoute(EntityTypeInterface $entity_type) {
+    if ($route = parent::getCanonicalRoute($entity_type)) {
+      $route->setOption('_admin_route', TRUE);
+      return $route;
+    }
+  }
+
+}

src/Routing/FixityCheckRouteSubscriber.php

@@ -0,0 +1,113 @@
+<?php
+
+namespace Drupal\dgi_fixity\Routing;
+
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Routing\RouteSubscriberBase;
+use Drupal\dgi_fixity\FixityCheckServiceInterface;
+use Symfony\Component\Routing\Route;
+use Symfony\Component\Routing\RouteCollection;
+
+/**
+ * Listens to the dynamic route events.
+ */
+class FixityCheckRouteSubscriber extends RouteSubscriberBase {
+
+  /**
+   * The fixity check service.
+   *
+   * @var \Drupal\dgi_fixity\FixityCheckServiceInterface
+   */
+  protected $fixity;
+
+  /**
+   * Subscriber for Fixity Check routes.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_manager
+   *   The entity type manager.
+   * @param \Drupal\dgi_fixity\FixityCheckServiceInterface $fixity
+   *   The fixity check service.
+   */
+  public function __construct(EntityTypeManagerInterface $entity_manager, FixityCheckServiceInterface $fixity) {
+    $this->entityTypeManager = $entity_manager;
+    $this->fixity = $fixity;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function alterRoutes(RouteCollection $collection) {
+    $supported_entity_types = array_merge(['fixity_check'], $this->fixity->fromEntityTypes());
+    $definitions = $this->entityTypeManager->getDefinitions();
+    foreach ($supported_entity_types as $entity_type_id) {
+      $entity_type = $definitions[$entity_type_id];
+      if ($route = $this->getFixityAuditRoute($entity_type)) {
+        $collection->add("entity.$entity_type_id.fixity_audit", $route);
+      }
+      if ($route = $this->getFixityCheckRoute($entity_type)) {
+        $collection->add("entity.$entity_type_id.fixity_check", $route);
+      }
+    }
+  }
+
+  /**
+   * Gets the fixity check 'Audit' route for the given entity type.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type.
+   *
+   * @return \Symfony\Component\Routing\Route|null
+   *   The generated route, if available.
+   */
+  protected function getFixityAuditRoute(EntityTypeInterface $entity_type) {
+    if ($fixity_audit = $entity_type->getLinkTemplate('fixity-audit')) {
+      $entity_type_id = $entity_type->id();
+      $route = new Route($fixity_audit);
+      $route
+        ->addDefaults([
+          '_controller' => '\Drupal\dgi_fixity\Controller\FixityCheckController::entityAudit',
+          '_title' => 'Audit',
+        ])
+        ->addRequirements([
+          '_permission' => 'view fixity checks',
+        ])
+        ->setOption('_admin_route', TRUE)
+        ->setOption('_fixity_entity_type_id', $entity_type_id)
+        ->setOption('parameters', [
+          $entity_type_id => ['type' => 'entity:' . $entity_type_id],
+        ]);
+      return $route;
+    }
+  }
+
+  /**
+   * Gets the fixity check 'Check' route for the given entity type.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type.
+   *
+   * @return \Symfony\Component\Routing\Route|null
+   *   The generated route, if available.
+   */
+  protected function getFixityCheckRoute(EntityTypeInterface $entity_type) {
+    if ($fixity_audit = $entity_type->getLinkTemplate('fixity-check')) {
+      $entity_type_id = $entity_type->id();
+      $route = new Route($fixity_audit);
+      $route
+        ->addDefaults([
+          '_entity_form' => "{$entity_type_id}.fixity-check",
+        ])
+        ->addRequirements([
+          '_permission' => 'administer fixity checks',
+        ])
+        ->setOption('_admin_route', TRUE)
+        ->setOption('_fixity_entity_type_id', $entity_type_id)
+        ->setOption('parameters', [
+          $entity_type_id => ['type' => 'entity:' . $entity_type_id],
+        ]);
+      return $route;
+    }
+  }
+
+}