islandora/islandora.module

<?php

/**
 * @file
 *
 * islandora.module: defines paths (drupal menu items) as entry points and acts
 *  as a hub for dispatching tasks to other modules.
 *
 * This file is part of Islandora.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with the program.  If not, see <http ://www.gnu.org/licenses/>.
 */

// Common datastreams
define('DS_COMP_STREAM', 'DS-COMPOSITE-MODEL');

// Permissions
define('FEDORA_VIEW', 'view fedora repository');
define('FEDORA_METADATA_EDIT', 'edit fedora metadata');
define('FEDORA_ADD_DS', 'add fedora datastreams');
define('FEDORA_INGEST', 'ingest fedora objects');
define('FEDORA_PURGE', 'delete fedora objects and datastreams');
define('FEDORA_MODIFY_STATE', 'modify fedora state');
define('FEDORA_MANAGE', 'manage fedora items');

// Hooks
define('ISLANDORA_VIEW_HOOK', 'islandora_view_object');
define('ISLANDORA_EDIT_HOOK', 'islandora_edit_object');
define('ISLANDORA_PRE_INGEST_HOOK', 'islandora_ingest_pre_ingest');
define('ISLANDORA_POST_INGEST_HOOK', 'islandora_ingest_post_ingest');
define('ISLANDORA_PRE_PURGE_OBJECT_HOOK', 'islandora_pre_purge_object');
define('ISLANDORA_POST_PURGE_OBJECT_HOOK', 'islandora_post_purge_object');
define('ISLANDORA_INGEST_STEP_HOOK', 'islandora_ingest_steps');
define('ISLANDORA_PRE_PURGE_DATASTREAM_HOOK', 'islandora_pre_purge_datastream');
define('ISLANDORA_POST_PURGE_DATASTREAM_HOOK', 'islandora_post_purge_datastream');
define('ISLANDORA_EDIT_DATASTREAM_HOOK', 'islandora_edit_datastream');

/**
 * Implements hook_menu().
 *
 * We need some standard entry points so we can have consistent urls for
 * different Object actions
 */
function islandora_menu() {
  $items = array();
  $items['admin/islandora'] = array(
    'title' => 'Islandora',
    'description' => "Configure settings associated with Islandora.",
    'access arguments' => array('administer site configuration'),
    'type' => MENU_NORMAL_ITEM,
  );
  $items['admin/islandora/configure'] = array(
    'title' => 'Configuration',
    'description' => 'Configure settings for Islandora.',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('islandora_repository_admin'),
    'file' => 'admin/islandora.admin.inc',
    'access arguments' => array('administer site configuration'),
    'type' => MENU_NORMAL_ITEM,
    'weight' => -1,
  );
  $items['admin/islandora/solution_packs'] = array(
    'title' => 'Solution packs',
    'description' => 'Install content models and collections required by installed solution packs.',
    'page callback' => 'islandora_solution_packs_admin',
    'access arguments' => array(FEDORA_ADD_DS),
    'file' => 'includes/solution_packs.inc',
    'type' => MENU_NORMAL_ITEM,
  );
  $items['islandora'] = array(
    'title' => 'Islandora Repository',
    'page callback' => 'islandora_view_default_object',
    'type' => MENU_NORMAL_ITEM,
    'access arguments' => array(FEDORA_VIEW),
  );
  $items['islandora/object/%islandora_object'] = array(
    'title' => 'Repository',
    'page callback' => 'islandora_view_object',
    'page arguments' => array(2),
    'type' => MENU_NORMAL_ITEM,
    'access callback' => 'islandora_object_access_callback',
    'access arguments' => array(FEDORA_VIEW, 2),
  );
  $items['islandora/object/%islandora_object/view'] = array(
    'title' => 'View',
    'type' => MENU_DEFAULT_LOCAL_TASK,
    'weight' => -1,
  );
  $items['islandora/object/%islandora_object/view/default'] = array(
    'title' => 'View',
    'type' => MENU_DEFAULT_LOCAL_TASK,
    'weight' => -1,
  );
  $items['islandora/object/%islandora_object/manage'] = array(
    'title' => 'Manage',
    'page callback' => 'islandora_edit_object',
    'page arguments' => array(2),
    'type' => MENU_LOCAL_TASK,
    'access callback' => 'islandora_object_access_callback',
    'access arguments' => array(FEDORA_MODIFY_STATE, 2),
  );
  $items['islandora/object/%islandora_object/manage/datastreams'] = array(
    'title' => 'Datastreams',
    'type' => MENU_DEFAULT_LOCAL_TASK,
    'weight' => -10,
  );
  $items['islandora/object/%islandora_object/manage/properties'] = array(
    'title' => 'Properties',
    'page callback' => 'drupal_get_form',
    'file' => 'includes/object_properties.form.inc',
    'page arguments' => array('islandora_object_properties_form', 2),
    'type' => MENU_LOCAL_TASK,
    'access callback' => 'islandora_object_access_callback',
    'access arguments' => array(FEDORA_MODIFY_STATE, 2),
    'weight' => -5,
  );
  $items['islandora/object/%islandora_object/delete'] = array(
    'title' => 'Delete object',
    'file' => 'includes/delete_object.form.inc',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('islandora_delete_object_form', 2),
    'type' => MENU_CALLBACK,
    'access callback' => 'islandora_object_access_callback',
    'access arguments' => array(FEDORA_PURGE, 2),
  );
  $items['islandora/object/%islandora_object/manage/datastreams/add'] = array(
    'title' => 'Add a datastream',
    'file' => 'includes/add_datastream.form.inc',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('islandora_add_datastream_form', 2),
    'type' => MENU_LOCAL_ACTION,
    'access callback' => 'islandora_object_access_callback',
    'access arguments' => array(FEDORA_ADD_DS, 2)
  );
  $items['islandora/object/%islandora_object/manage/datastreams/add/autocomplete'] = array(
    'file' => 'includes/add_datastream.form.inc',
    'page callback' => 'islandora_add_datastream_form_autocomplete_callback',
    'page arguments' => array(2),
    'type' => MENU_CALLBACK,
    'access callback' => 'islandora_object_access_callback',
    'access arguments' => array(FEDORA_ADD_DS, 2)
  );
  $items['islandora/object/%islandora_object/datastream/%islandora_datastream'] = array(
    'title' => 'View datastream',
    'page callback' => 'islandora_view_datastream',
    'page arguments' => array(4, FALSE),
    'type' => MENU_CALLBACK,
    'file' => 'includes/datastream.inc',
    'access callback' => 'islandora_object_datastream_access_callback',
    'access arguments' => array(FEDORA_VIEW, 2, 4),
    'load arguments' => array(2),
  );
  $items['islandora/object/%islandora_object/datastream/%islandora_datastream/view'] = array(
    'title' => 'View datastream',
    'type' => MENU_DEFAULT_LOCAL_TASK,
  );
  $items['islandora/object/%islandora_object/datastream/%islandora_datastream/download'] = array(
    'title' => 'Download datastream',
    'page callback' => 'islandora_download_datastream',
    'page arguments' => array(4),
    'type' => MENU_CALLBACK,
    'file' => 'includes/datastream.inc',
    'access callback' => 'islandora_object_datastream_access_callback',
    'access arguments' => array(FEDORA_VIEW, 2, 4),
    'load arguments' => array(2),
  );
  $items['islandora/object/%islandora_object/datastream/%islandora_datastream/edit'] = array(
    'title' => 'Edit datastream',
    'page callback' => 'islandora_edit_datastream',
    'page arguments' => array(4),
    'type' => MENU_CALLBACK,
    'file' => 'includes/datastream.inc',
    'access callback' => 'islandora_object_datastream_access_callback',
    'access arguments' => array(FEDORA_METADATA_EDIT, 2, 4),
    'load arguments' => array(2),
  );
  $items['islandora/object/%islandora_object/datastream/%islandora_datastream/delete'] = array(
    'title' => 'Delete data stream',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('islandora_delete_datastream_form', 4),
    'file' => 'includes/delete_datastream.form.inc',
    'type' => MENU_CALLBACK,
    'access callback' => 'islandora_object_datastream_access_callback',
    'access arguments' => array(FEDORA_PURGE, 2, 4),
    'load arguments' => array(2),
  );
  $items['islandora/ingest'] = array(
    'title' => 'Add an Object',
    'page callback' => 'islandora_ingest_callback',
    'file' => 'includes/ingest.menu.inc',
    'type' => MENU_SUGGESTED_ITEM,
    'access arguments' => array(FEDORA_INGEST),
  );
  return $items;
}

/**
 * Implements hook_admin_paths().
 */
function islandora_admin_paths() {
  $paths = array();
  $paths['islandora/object/*/manage*'] = TRUE;
  $paths['islandora/object/*/delete'] = TRUE;
  $paths['islandora/object/*/datastream/*/edit'] = TRUE;
  return $paths;
}

/**
 * Implements hook_theme().
 */
function islandora_theme() {
  return array(
    // default object template
    'islandora_default' => array(
      'file' => 'theme/islandora.theme.inc',
      'template' => 'theme/islandora-object',
      'variables' => array('islandora_object' => NULL),
    ),
    // default edit page
    'islandora_default_edit' => array(
      'file' => 'theme/islandora.theme.inc',
      'template' => 'theme/islandora-object-edit',
      'variables' => array('islandora_object' => NULL),
    ),
    // admin table for solution pack viewer selection
    'islandora_viewers_table' => array(
      'file' => 'includes/solution_packs.inc',
      'render element' => 'form',
    ),
  );
}

/**
 * Implements hook_permission().
 */
function islandora_permission() {
  return array(
    FEDORA_VIEW => array(
      'title' => t('View repository objects and datastreams'),
      'description' => t('View objects in the repository and their associated datastreams. Note: Fedora XACML security policies may override this permission.')
    ),
    FEDORA_ADD_DS => array(
      'title' => t('Add datastreams to repository objects'),
      'description' => t('Add datastreams to objects in the repository. Note: Fedora XACML security policies may override this position.')
    ),
    FEDORA_METADATA_EDIT => array(
      'title' => t('Edit metadata'),
      'description' => t('Edit metadata for objects in the repository.')
    ),
    FEDORA_INGEST => array(
      'title' => t('Create new repository objects'),
      'description' => t('Create new objects in the repository.')
    ),
    FEDORA_PURGE => array(
      'title' => t('Permanently remove objects from the repository'),
      'description' => t('Permanently remove objects from the repository.')
    ),
    FEDORA_MODIFY_STATE => array(
      'title' => t('Change repository object states'),
      'description' => t('Change the state of objects in the repository (e.g. from Active to Inactive).')
    ),
    FEDORA_MANAGE => array(
      'title' => t('View object management tabs'),
      'description' => t('View tabs that provide object management functions.')
    )
  );
}

/**
 * Implements hook_forms().
 */
function islandora_forms($form_id) {
  $forms = array();
  if (strpos($form_id, 'islandora_solution_pack_form_') !== FALSE) {
    $forms[$form_id] = array(
      'callback' => 'islandora_solution_pack_form',
    );
  }
  return $forms;
}

/**
 * Checks whether the user can access the given object with the given
 * permission.
 *
 * Checks for object existance, accessiblitly, namespace permissions,
 * and user permissions
 *
 * @see islandora_object_load() To find potential solutions to enable
 *   page not found errors.
 *
 * @param string $perm
 *   The user permission to test for.
 * @param FedoraObject $object
 *   The object to test, if NULL given the object doesn't exist or is
 *   inaccessible.
 *
 * @return boolean
 *   TRUE if the user is allowed to access this object, FALSE otherwise.
 */
function islandora_object_access_callback($perm, $object = NULL) {
  module_load_include('inc', 'islandora', 'includes/utilities');
  return user_access($perm) && is_object($object) && islandora_namespace_accessible($object->id);
}

/**
 * Checks whether the user can access the given object and datastream with
 * the given permission.
 *
 * Checks for object existance, accessiblitly, namespace permissions,
 * and user permissions
 *
 * @see islandora_object_load() To find potential solutions to enable page
 *   not found errors.
 *
 * @param string $perm
 *   The user permission to test for.
 * @param FedoraObject $object
 *   The object to test, if NULL given the object doesn't exist or is
 *   inaccessible.
 * @param FedoraDatastream $datastream
 *   The datastream to test, if NULL given the datastream doesn't exist
 *   or is inaccessible.
 *
 * @return boolean
 *   TRUE if the user is allowed to access this object, FALSE otherwise.
 */
function islandora_object_datastream_access_callback($perm, $object = NULL, $datastream = NULL) {
  module_load_include('inc', 'islandora', 'includes/utilities');
  return user_access($perm) && is_object($object) && islandora_namespace_accessible($object->id) && is_object($datastream);
}

/**
 * Renders the given objects manage page.
 *
 * Its possible to modify the output of this function if 'ISLANDORA_EDIT_HOOK'
 * is implemented in other modules.
 *
 * If no modules implement 'ISLANDORA_EDIT_HOOK' then this function returns the
 *  default manage view.
 *
 * @param FedoraObject $object
 *   The object to manage.
 *
 * @return string
 *   The HTML repersentation of the manage object page.
 */
function islandora_edit_object(FedoraObject $object) {
  module_load_include('inc', 'islandora', 'includes/utilities');
  $output = array();
  foreach (islandora_build_hook_list(ISLANDORA_EDIT_HOOK, $object->models) as $hook) {
    $temp = module_invoke_all($hook, $object);
    if (!empty($temp)) {
      $output = array_merge_recursive($output, $temp);
    }
  }
  if (empty($output)) {
    // Add in the default, if we did not get any results.
    $output = islandora_default_islandora_edit_object($object);
  }
  arsort($output);
  drupal_alter(ISLANDORA_EDIT_HOOK, $object, $output);
  return implode('', $output);
}

/**
 * Renders the default manage object page for the given object.
 *
 * @param FedoraObject $object
 *   The object used to render the manage object page.
 *
 * @return array
 *   The default rendering of the object manage page, indexed at
 *   'Default Edit output'.
 */
function islandora_default_islandora_edit_object(FedoraObject $object) {
  $output = theme('islandora_default_edit', array('islandora_object' => $object));
  return array('Default Edit output' => $output);
}

/**
 * Page callback for the path "islandora".
 *
 * Redirects to the view of the object indicated by the Drupal variable
 * 'islandora_repository_pid'.
 */
function islandora_view_default_object() {
  $pid = variable_get('islandora_repository_pid', 'islandora:root');
  drupal_goto("islandora/object/$pid");
}

/**
 * Renders the default view object page for the given object.
 *
 * Modules should implement ISLANDORA_VIEW_HOOK for the Fedora Content
 * models that their modules want to provide a view for.
 *
 * If no modules implement the hook then the default view object page
 *  will be rendered.
 *
 * @param FedoraObject $object
 *   The object to view.
 *
 * @return string
 *   The html repersentation of this object.
 */
function islandora_view_object(FedoraObject $object) {
  module_load_include('inc', 'islandora', 'includes/breadcrumb');
  module_load_include('inc', 'islandora', 'includes/utilities');
  drupal_set_breadcrumb(islandora_get_breadcrumbs($object));
  // Optional pager parameters
  $page_number = (empty($_GET['page'])) ? '1' : $_GET['page'];
  $page_size = (empty($_GET['pagesize'])) ? '10' : $_GET['pagesize'];
  $output = array();
  foreach (islandora_build_hook_list(ISLANDORA_VIEW_HOOK, $object->models) as $hook) {
    // @todo Remove page number and size from this hook, implementers of the
    // hook should use drupal page handling directly.
    $temp = module_invoke_all($hook, $object, $page_number, $page_size);
    if (!empty($temp)) {
      $output = array_merge_recursive($output, $temp);
    }
  }
  if (empty($output)) {
    // No results, use the default view.
    $output = islandora_default_islandora_view_object($object);
  }
  arsort($output);
  drupal_alter(ISLANDORA_VIEW_HOOK, $object, $output);
  return implode('', $output);
}

/**
 * Renders the default view object page for the given object.
 *
 * @param FedoraObject $object
 *   The object used to render the view object page.
 *
 * @return array
 *   The default rendering of the object view page, indexed at 'Default output'.
 */
function islandora_default_islandora_view_object($object) {
  $output = theme('islandora_default', array('islandora_object' => $object));
  return array('Default output' => $output);
}

/**
 * A helper function to get a connection and return an object for objects
 * specified in the menu path as '%islandora_object'.
 *
 * @param string $object_id
 *   The pid of an object in the menu path identified by '%islandora_object'.
 *
 * @return FedoraObject
 *   If the given object id exists in the repository then this returns a
 *   FedoraObject.
 *   If no object was found it returns FALSE which triggers
 *   drupal_page_not_found().
 *   If the object was inaccessible then NULL is returned, and the
 *   access callback is expected to catch that case, triggering
 *   drupal_access_denied().
 */
function islandora_object_load($object_id) {
  module_load_include('inc', 'islandora', 'includes/IslandoraTuque');
  $tuque = islandora_get_tuque_connection();
  if ($tuque) {
    try {
      $object = $tuque->repository->getObject($object_id);
      drupal_alter('islandora_object', $object);
      return $object;
    } catch (Exception $e) {
      if ($e->getCode() == '404') {
        return FALSE;
      }
      else {
        return NULL;
      }
    }
  }
  else {
    IslandoraTuque::getError();
  }
  // Assuming access denied in all other cases for now.
  return NULL;
}

/**
 * A helper function to get an datastream specified as '%islandora_datastream'
 * for the object specified in the menu path as '%islandora_object'.
 *
 * Its up to the access callbacks and menu callbacks to trigger
 * drupal_access_denied() when appropriate.
 *
 * @param string $datastream_id
 *   The dsid of the datastream specified as '%islandora_datastream' to fetch
 *   from the given object in the menu path identified by '%islandora_object'.
 *
 * $param string $object_id
 *   The object to load the datastream from.
 *
 * @return FedoraDatastream
 *   If the given datastream ID exists then this returns a FedoraDatastream
 *   object, otherwise it returns NULL which triggers drupal_page_not_found().
 */
function islandora_datastream_load($datastream_id, $object_id) {
  $object = islandora_object_load($object_id);

  if (!$object) {
    return NULL;
  }

  return $object[$datastream_id];
}

/**
 * Content model, collection view and collection policy datastreams may now
 * optionally define a version number in their top-level XML element as an
 * attribute, as in:
 *   <content_model name="Collection" version="2" ...
 *
 * @param object $item
 * @param string $dsid
 * @param string $datastream_file
 * @return
 *   int, or NULL if no version attribute was found.
 */
function islandora_get_islandora_datastream_version($item = NULL, $dsid = NULL, $datastream_file = NULL) {
  $return = NULL;
  // @TODO, need better check for $item
  if ($item && $item[$dsid]) {
    $doc = simplexml_load_string($item[$dsid]->content);
  }
  elseif (!empty($datastream_file)) {
    $doc = simplexml_load_file($datastream_file);
  }

  if (!empty($doc) && $version = (int)$doc->attributes()->version) {
    $return = $version;
  }

  return $return;
}

/**
 * Implements hook_islandora_required_objects().
 */
function islandora_islandora_required_objects() {
  $module_path = drupal_get_path('module', 'islandora');
  return array(
    'islandora' => array(
      'title' => 'Islandora',
      'objects' => array(
        array(
          'pid' => 'islandora:root',
          'label' => 'Top-level collection',
          'cmodel' => 'islandora:collectionCModel',
          'datastreams' => array(
            array(
              'dsid' => 'COLLECTION_POLICY',
              'label' => 'Collection policy',
              'mimetype' => 'text/xml',
              'control_group' => 'X',
              'datastream_file' => "$module_path/xml/islandora_collection_policy.xml",
            ),
            array(
              'dsid' => 'TN',
              'label' => 'Thumbnail',
              'mimetype' => 'image/png',
              'control_group' => 'M',
              'datastream_file' => "$module_path/images/folder.png",
            ),
          ),
        ),
      ),
    ),
  );
}

/**
 * Implements islandora_undeleteable_datastreams().
 */
function islandora_islandora_undeletable_datastreams(array $models) {
  return array('DC');
}

/**
 * Ingest the given object into Fedora calling its pre/post hooks as well.
 *
 * @todo will be cleaned up in the future
 *
 * @param NewFedoraObject $object
 *   An ingestable FedoraObject.
 *
 * @return FedoraObject
 *   The ingested FedoraObject, after running the pre/post ingest hooks.
 */
function islandora_add_object(NewFedoraObject &$object) {
  islandora_pre_add_object($object);
  $object->repository->ingestObject($object);
  islandora_post_add_object($object);
  return $object;
}

/**
 * Calls the ISLANDORA_PRE_INGEST_HOOK hooks.
 *
 * @param NewFedoraObject $object
 *   An ingestable FedoraObject.
 */
function islandora_pre_add_object(NewFedoraObject $object) {
  module_load_include('inc', 'islandora', 'includes/utilities');
  foreach (islandora_build_hook_list(ISLANDORA_PRE_INGEST_HOOK, $object->models) as $hook) {
    module_invoke_all($hook, $object);
  }
}


/**
 * Calls the ISLANDORA_POST_INGEST_HOOK hooks.
 *
 * @param FedoraObject $object
 *   A recently ingestable FedoraObject.
 */
function islandora_post_add_object(FedoraObject $object) {
  foreach (islandora_build_hook_list(ISLANDORA_POST_INGEST_HOOK, $object->models) as $hook) {
    module_invoke_all($hook, $object);
  }
}

/**
 * Deletes the given object into Fedora calling its pre/post hooks as well.
 *
 * @param FedoraObject $object
 *   An object to delete.
 *
 * @return FedoraObject
 *   The ingested FedoraObject, after running the pre/post ingest hooks.
 */
function islandora_delete_object(FedoraObject &$object) {
  $object_id = $object->id;
  $models = $object->models;
  $action = islandora_pre_delete_object($object);
  switch ($action) {
    case 'blocked':
      // Do nothing.
      return FALSE;
    case 'delete':
      // Change the state to deleted.
      $object->delete();
      islandora_post_delete_object($object_id, $models);
      return TRUE;
    default:
      // Purge
      $object->repository->purgeObject($object_id);
      islandora_post_delete_object($object_id, $models);
      $object = NULL;
      return TRUE;
  }
}

/**
 * Calls the ISLANDORA_PRE_PURGE_OBJECT_HOOK hooks.
 *
 * @param FedoraObject $object
 *   The object that is about to be deleted.
 */
function islandora_pre_delete_object(FedoraObject $object) {
  module_load_include('inc', 'islandora', 'includes/utilities');
  $results = array();
  foreach (islandora_build_hook_list(ISLANDORA_PRE_PURGE_OBJECT_HOOK, $object->models) as $hook) {
    $results = array_merge_recursive($results, module_invoke_all($hook, $object));
  }
  $action = (isset($results['block']) && $results['block']) ? 'block' : FALSE;
  $action = (!$action && isset($results['delete']) && $results['delete']) ? 'delete' : $action;
  $action = !$action ? 'purge' : $action;
  return $action;
}

/**
 * Calls the ISLANDORA_POST_PURGE_OBJECT_HOOK hooks.
 *
 * @param string $object_id
 *   The object id of an the recently deleted object.
 * @param array $models
 *   The list of content models the delete object subsribed to.
 */
function islandora_post_delete_object($object_id, array $models) {
  module_load_include('inc', 'islandora', 'includes/utilities');
  foreach (islandora_build_hook_list(ISLANDORA_POST_PURGE_OBJECT_HOOK, $models) as $hook) {
    module_invoke_all($hook, $object_id, $models);
  }
}

/**
 * Delete's/Purges the given datastream.
 *
 * @throws Exception
 *  Which types are undefined, but more than likely because of the hooks
 *  there will be several kinds.
 *
 * @param FedoraDatastream $datastream
 *   The datastream to delete.
 *
 * @return boolean
 *   TRUE is returned if the datastream was Deleted/Purged, FALSE if it was
 *   blocked.
 */
function islandora_delete_datastream(FedoraDatastream &$datastream) {
  $datastream_id = $datastream->id;
  $object = $datastream->parent;
  $action = islandora_pre_delete_datastream($datastream);
  switch ($action) {
    case 'blocked':
      // Do nothing.
      return FALSE;
    case 'delete':
      // Change the state to deleted.
      $object[$datastream_id]->state = 'D';
      // @todo Differentiate between delete/purge in the hooks.
      islandora_post_delete_datastream($object, $datastream_id);
      return TRUE;
    default:
      // Purge
      $object->purgeDatastream($datastream_id);
      islandora_post_delete_datastream($object, $datastream_id);
      $datastream = NULL;
      return TRUE;
  }
}

/**
 * The default behaviour is to 'purge' the datastream but this can be overridden
 * by modules that implement the 'islandora_pre_purge_datastream' hook.
 *
 * @todo make this an alter.
 *
 * The returned array can include a 'block' => TRUE
 * pair which will prevent the datastream from being deleted if it particularly
 * needed for a certain function. Returning 'delete' => TRUE will cause the
 * datastream to be put into a deleted state.
 *
 * @param FedoraDatastream $datastream
 *   The datastream to delete.
 *
 * @return string
 *   The action to take when deleting the given datastream, either 'purge',
 *   'delete', or 'block'.
 */
function islandora_pre_delete_datastream(FedoraDatastream $datastream) {
  module_load_include('inc', 'islandora', 'includes/utilities');
  $results = array();
  foreach (islandora_build_hook_list(ISLANDORA_PRE_PURGE_DATASTREAM_HOOK, $datastream->parent->models) as $hook) {
    // Not sure this will work the greatest, probably an alter would be better..
    $results = array_merge_recursive($results, module_invoke_all($hook, $datastream));
  }
  $action = (isset($results['block']) && $results['block']) ? 'block' : FALSE;
  $action = (!$action && isset($results['delete']) && $results['delete']) ? 'delete' : $action;
  $action = !$action ? 'purge' : $action;
  return $action;
}

/**
 * Calls the post purge datastream hooks.
 *
 * @todo Should differentiate between purging/deleting.
 *
 * @param FedoraObject $object
 *   The parent object of the deleted datastream.
 * @param string $datastream_id
 *   The datastream id of the deleted datastream.
 */
function islandora_post_delete_datastream(FedoraObject $object, $datastream_id) {
  module_load_include('inc', 'islandora', 'includes/utilities');
  foreach (islandora_build_hook_list(ISLANDORA_POST_PURGE_DATASTREAM_HOOK, $object->models) as $hook) {
    module_invoke_all($hook, $object, $datastream_id);
  }
}