Merge pull request #374 from jonathangreen/7.x-add-ds-history

7.x add ds history

includes/datastream.inc

@@ -26,8 +26,19 @@ function islandora_download_datastream(AbstractDatastream $datastream) {
  * @param bool $download
  *   If TRUE the file is download to the user computer for viewing otherwise it
  *   will attempt to display in the browser natively.
+ * @param int $version
+ *   The version of the datastream to display
  */
-function islandora_view_datastream(AbstractDatastream $datastream, $download = FALSE) {
+function islandora_view_datastream(AbstractDatastream $datastream, $download = FALSE, $version = NULL) {
+  if ($version !== NULL) {
+    if (isset($datastream[$version])) {
+      $datastream = $datastream[$version];
+    }
+    else {
+      return drupal_not_found();
+    }
+  }
+
   header_remove('Cache-Control');
   header_remove('Expires');
   header('Content-type: ' . $datastream->mimetype);
@@ -69,12 +80,31 @@ function islandora_datastream_get_human_readable_size(AbstractDatastream $datast
  *
  * @param AbstractDatastream $datastream
  *   The datastream to generated the url to.
+ * @param string $type
+ *   One of:
+ *   - download
+ *   - view
+ * @param int $version
+ *   (Optional) The version of the datastream to get a URL for.
  *
  * @return string
  *   either the 'view' or 'download' url for the given datastream.
  */
-function islandora_datastream_get_url(AbstractDatastream $datastream, $type = 'download') {
+function islandora_datastream_get_url(AbstractDatastream $datastream, $type = 'download', $version = NULL) {
-  return $datastream->controlGroup == 'R' ? $datastream->url : "islandora/object/{$datastream->parent->id}/datastream/{$datastream->id}/$type";
+  if ($version === NULL) {
+    $link = "islandora/object/{$datastream->parent->id}/datastream/{$datastream->id}/$type";
+  }
+  else {
+    $link = "islandora/object/{$datastream->parent->id}/datastream/{$datastream->id}/version/$version/$type";
+    $datastream = $datastream[$version];
+  }
+
+  if ($datastream->controlGroup == 'R') {
+    return $datastream->url;
+  }
+  else {
+    return $link;
+  }
 }
 
 /**

includes/datastream.version.inc

@@ -0,0 +1,125 @@
+<?php
+/**
+ * @file
+ * The form displayed that shows the datastream version history.
+ */
+
+/**
+ * Function that returns markup for the datastream versions page.
+ */
+function islandora_datastream_version_table($datastream) {
+  module_load_include('inc', 'islandora', 'includes/datastream');
+  module_load_include('inc', 'islandora', 'includes/utilities');
+
+  drupal_set_title(t("@dsid Previous Versions", array('@dsid' => $datastream->id)));
+
+  $header = array();
+  $header[] = array('data' => t('Created Date'));
+  $header[] = array('data' => t('Size'));
+  $header[] = array('data' => t('Label'));
+  $header[] = array('data' => t('Mime type'));
+  $header[] = array('data' => t('Operations'));
+  $rows = array();
+
+  foreach ($datastream as $version => $datastream_version) {
+    $row = array();
+    $row[] = array(
+      'class' => 'datastream-date',
+      'data' => theme('islandora_datastream_view_link', array(
+        'datastream' => $datastream,
+        'label' => $datastream_version->createdDate->format(DATE_RFC850),
+        'version' => $version,
+      )),
+    );
+    $row[] = array(
+      'class' => 'datastream-size',
+      'data' => islandora_datastream_get_human_readable_size($datastream_version),
+    );
+    $row[] = array(
+      'class' => 'datastream-label',
+      'data' => $datastream_version->label,
+    );
+    $row[] = array(
+      'class' => 'datastream-mime',
+      'data' => $datastream_version->mimeType,
+    );
+    $row[] = array(
+      'class' => 'datastream-delete',
+      'data' => theme('islandora_datastream_delete_link', array(
+        'datastream' => $datastream,
+        'version' => $version,
+      )),
+    );
+    $rows[] = $row;
+  }
+
+  return theme('table', array('header' => $header, 'rows' => $rows));
+}
+
+/**
+ * The admin delete datastream form.
+ *
+ * @param array $form
+ *   The Drupal form.
+ * @param array $form_state
+ *   The Drupal form state.
+ * @param AbstractDatastream $datastream
+ *   The datastream to be deleted.
+ *
+ * @return array
+ *   The drupal form definition.
+ */
+function islandora_delete_datastream_version_form(array $form, array &$form_state, AbstractDatastream $datastream, $version) {
+  if (!isset($datastream[$version]) || count($datastream) < 2) {
+    return drupal_not_found();
+  }
+
+  $form_state['datastream'] = $datastream;
+  $form_state['version'] = $version;
+  return confirm_form($form,
+    t('Are you sure you want to delete version @version of the @dsid datastream?', array('@dsid' => $datastream->id, '@version' => $version)),
+    "islandora/object/{$datastream->parent->id}",
+    t('This action cannot be undone.'),
+    t('Delete'),
+    t('Cancel')
+  );
+}
+
+/**
+ * Submit handler for the delete datastream form.
+ *
+ * Purges/Delete's the given AbstractDatastream if possible.
+ *
+ * The ISLANDORA_PRE_PURGE_DATASTREAM_HOOK will query other modules as to
+ * whether the given FedoraDatastream
+ * should be: blocked from purging; state set to 'Deleted'; or purged.
+ *
+ * @param array $form
+ *   The Drupal form.
+ * @param array $form_state
+ *   The Drupal form state.
+ */
+function islandora_delete_datastream_version_form_submit(array $form, array &$form_state) {
+  $datastream = $form_state['datastream'];
+  $version = $form_state['version'];
+
+  $datastream_id = $datastream->id;
+  $object = $datastream->parent;
+
+  try {
+    unset($datastream[$version]);
+  }
+  catch (Exception $e) {
+    drupal_set_message(t('Error deleting version %v of %s datastream from object %o %e', array(
+          '%v' => $version,
+          '%s' => $datastream_id,
+          '%o' => $object->label,
+          '%e' => $e->getMessage())), 'error');
+  }
+
+  drupal_set_message(t('%d datastream version successfully deleted from Islandora object %o', array(
+        '%d' => $datastream_id,
+        '%o' => $object->label)));
+
+  $form_state['redirect'] = "islandora/object/{$object->id}/datastream/{$datastream->id}/version";
+}

islandora.info

@@ -17,4 +17,5 @@ files[] = tests/hooks.test
 files[] = tests/ingest.test
 files[] = tests/hooked_access.test
 files[] = tests/islandora_manage_permissions.test
+files[] = tests/datastream_versions.test
 php = 5.3

islandora.module

@@ -33,6 +33,7 @@ define('FEDORA_ADD_DS', 'add fedora datastreams');
 define('FEDORA_INGEST', 'ingest fedora objects');
 define('FEDORA_PURGE', 'delete fedora objects and datastreams');
 define('FEDORA_MANAGE_PROPERTIES', 'manage object properties');
+define('ISLANDORA_VIEW_DATASTREAM_HISTORY', 'view old datastream versions');
 
 // Hooks.
 define('ISLANDORA_VIEW_HOOK', 'islandora_view_object');
@@ -233,6 +234,36 @@ function islandora_menu() {
     'access arguments' => array(FEDORA_PURGE, 4),
     'load arguments' => array(2),
   );
+  $items['islandora/object/%islandora_object/datastream/%islandora_datastream/version'] = array(
+    'title' => 'Datastream Versions',
+    'page arguments' => array(4),
+    'page callback' => 'islandora_datastream_version_table',
+    'file' => 'includes/datastream.version.inc',
+    'type' => MENU_CALLBACK,
+    'access callback' => 'islandora_datastream_access',
+    'access arguments' => array(ISLANDORA_VIEW_DATASTREAM_HISTORY, 4),
+    'load arguments' => array(2),
+  );
+  $items['islandora/object/%islandora_object/datastream/%islandora_datastream/version/%/delete'] = array(
+    'title' => 'Delete datastream version',
+    'page arguments' => array('islandora_delete_datastream_version_form', 4, 6),
+    'page callback' => 'drupal_get_form',
+    'file' => 'includes/datastream.version.inc',
+    'type' => MENU_CALLBACK,
+    'access callback' => 'islandora_datastream_access',
+    'access arguments' => array(FEDORA_PURGE, 4),
+    'load arguments' => array(2),
+  );
+  $items['islandora/object/%islandora_object/datastream/%islandora_datastream/version/%/view'] = array(
+    'title' => 'View datastream version',
+    'page callback' => 'islandora_view_datastream',
+    'page arguments' => array(4, FALSE, 6),
+    'type' => MENU_CALLBACK,
+    'file' => 'includes/datastream.inc',
+    'access callback' => 'islandora_datastream_access',
+    'access arguments' => array(ISLANDORA_VIEW_DATASTREAM_HISTORY, 4),
+    'load arguments' => array(2),
+  );
   $items['islandora/object/%islandora_object/print'] = array(
     'title' => 'Print Object',
     'page callback' => 'islandora_print_object',
@@ -268,8 +299,9 @@ function islandora_menu() {
 function islandora_admin_paths() {
   $paths = array();
   $paths['islandora/object/*/manage*'] = TRUE;
-  $paths['islandora/object/*/delete'] = TRUE;
+  $paths['islandora/object/*/delete*'] = TRUE;
   $paths['islandora/object/*/datastream/*/edit'] = TRUE;
+  $paths['islandora/object/*/datastream/*/versions'] = TRUE;
   return $paths;
 }
 
@@ -329,16 +361,24 @@ function islandora_theme() {
     ),
     'islandora_datastream_delete_link' => array(
       'file' => 'theme/theme.inc',
-      'variables' => array('datastream' => NULL),
+      'variables' => array('datastream' => NULL, 'version' => NULL),
     ),
     'islandora_datastream_view_link' => array(
       'file' => 'theme/theme.inc',
-      'variables' => array('datastream' => NULL),
+      'variables' => array(
+        'datastream' => NULL,
+        'version' => NULL,
+        'label' => NULL,
+      ),
     ),
     'islandora_datastream_download_link' => array(
       'file' => 'theme/theme.inc',
       'variables' => array('datastream' => NULL),
     ),
+    'islandora_datastream_version_link' => array(
+      'file' => 'theme/theme.inc',
+      'variables' => array('datastream' => NULL),
+    ),
   );
 }
 
@@ -371,6 +411,10 @@ function islandora_permission() {
       'title' => t('Manage object properties'),
       'description' => t('Modify object labels, owner IDs, and states.'),
     ),
+    ISLANDORA_VIEW_DATASTREAM_HISTORY => array(
+      'title' => t('View datastream history'),
+      'description' => t('View all previous versions of a datastream.'),
+    ),
   );
 }
 

tests/datastream_versions.test

@@ -0,0 +1,198 @@
+<?php
+
+/**
+ * @file
+ * Tests that datastream versions code works as intended
+ */
+
+class IslandoraDatastreamVersionTestCase extends IslandoraWebTestCase {
+
+  /**
+   * Gets info to display to describe this test.
+   *
+   * @see IslandoraWebTestCase::getInfo()
+   */
+  public static function getInfo() {
+    return array(
+      'name' => 'Islandora Datastream Versions',
+      'description' => 'Tests the functionality related to datastream versions in Islandora.',
+      'group' => 'Islandora',
+    );
+  }
+
+  /**
+   * Create an object with many datastram versions.
+   *
+   * @see IslandoraWebTestCase::setUp()
+   */
+  public function setUp() {
+    parent::setUp();
+
+    $this->pid = $this->randomName() . ":" . $this->randomName();
+    $tuque = islandora_get_tuque_connection();
+    $object = $tuque->repository->constructObject($this->pid);
+    $object = $tuque->repository->ingestObject($object);
+    $this->dsid = $this->randomName();
+    $ds = $object->constructDatastream($this->dsid);
+    $ds->label = 'Test';
+    $ds->content = 'test';
+    $object->ingestDatastream($ds);
+
+    // Create three versions.
+    $ds->mimetype = 'application/pdf';
+    $ds->label = 'jaaaaa maaaan';
+    $ds->content = 'Tests... are the bests.';
+  }
+
+  /**
+   * Free any objects/resources created for this test.
+   *
+   * @see IslandoraWebTestCase::tearDown()
+   */
+  public function tearDown() {
+    $tuque = islandora_get_tuque_connection();
+    $tuque->repository->purgeObject($this->pid);
+
+    parent::tearDown();
+  }
+
+  /**
+   * Check if the user can see datastream versions in the datastream table.
+   */
+  public function testSeeDatastreamVersions() {
+    $user = $this->drupalCreateUser(array(
+      'view fedora repository objects',
+      'ingest fedora objects',
+      'view old datastream versions',
+      'add fedora datastreams',
+    ));
+    $this->drupalLogin($user);
+    $this->drupalGet("islandora/object/{$this->pid}/manage/datastreams");
+    $this->assertLink($this->dsid);
+    $this->assertLink("4");
+    $encoded_pid = urlencode($this->pid);
+    $this->assertLinkByHref("islandora/object/$encoded_pid/datastream/{$this->dsid}/version");
+  }
+
+  /**
+   * Check that users without permission cannot see datastream versions.
+   */
+  public function testNotSeeDatastreamVersions() {
+    $user = $this->drupalCreateUser(array(
+      'view fedora repository objects',
+      'ingest fedora objects',
+      'add fedora datastreams',
+    ));
+    $this->drupalLogin($user);
+    $this->drupalGet("islandora/object/{$this->pid}/manage/datastreams");
+    $this->assertLink($this->dsid);
+    $this->assertNoLink("4");
+    $encoded_pid = urlencode($this->pid);
+    $this->assertNoLinkByHref("islandora/object/$encoded_pid/datastream/{$this->dsid}/version");
+  }
+
+  /**
+   * Check that users without permission cannot see datastream version pages.
+   */
+  public function testDatastreamVersionPermissions() {
+    $this->drupalGet("islandora/object/{$this->pid}/datastream/{$this->dsid}/version");
+    $this->assertResponse(403);
+    $this->drupalGet("islandora/object/{$this->pid}/datastream/{$this->dsid}/version/0/view");
+    $this->assertResponse(403);
+  }
+
+  /**
+   * Check that the proper infomration is displayed on the ds version page.
+   */
+  public function testDatastreamVersionPage() {
+    $user = $this->drupalCreateUser(array(
+      'view old datastream versions',
+    ));
+    $this->drupalLogin($user);
+    $this->drupalGet("islandora/object/{$this->pid}/datastream/{$this->dsid}/version");
+    $this->assertNoLink("Delete");
+    $this->assertText("text/xml");
+    $this->assertText("application/pdf");
+    $this->assertText("jaaaaa maaaan");
+    $this->assertText("Test");
+
+    $encoded_pid = urlencode($this->pid);
+    $this->assertLinkByHref("islandora/object/$encoded_pid/datastream/{$this->dsid}/version/0/view");
+    $this->assertLinkByHref("islandora/object/$encoded_pid/datastream/{$this->dsid}/version/1/view");
+    $this->assertLinkByHref("islandora/object/$encoded_pid/datastream/{$this->dsid}/version/2/view");
+    $this->assertLinkByHref("islandora/object/$encoded_pid/datastream/{$this->dsid}/version/3/view");
+  }
+
+  /**
+   * Make sure the correct content is displayed for each datastream version.
+   */
+  public function testDatastreamVersionContent() {
+    $user = $this->drupalCreateUser(array(
+      'view old datastream versions',
+    ));
+    $this->drupalLogin($user);
+    $this->drupalGet("islandora/object/{$this->pid}/datastream/{$this->dsid}/version/3/view");
+    $content = $this->drupalGetContent();
+    if ($content != 'test') {
+      $this->fail("Incorrect datastream content");
+    }
+    $this->drupalGet("islandora/object/{$this->pid}/datastream/{$this->dsid}/version/2/view");
+    $content = $this->drupalGetContent();
+    if ($content != 'test') {
+      $this->fail("Incorrect datastream content");
+    }
+    $this->drupalGet("islandora/object/{$this->pid}/datastream/{$this->dsid}/version/1/view");
+    $content = $this->drupalGetContent();
+    if ($content != 'test') {
+      $this->fail("Incorrect datastream content");
+    }
+    $this->drupalGet("islandora/object/{$this->pid}/datastream/{$this->dsid}/version/0/view");
+    $content = $this->drupalGetContent();
+    if ($content != 'Tests... are the bests.') {
+      $this->fail("Incorrect datastream content");
+    }
+    $this->drupalGet("islandora/object/{$this->pid}/datastream/{$this->dsid}/version/5/view");
+    $this->assertResponse(404);
+  }
+
+  /**
+   * Make sure you can delete datastream versions.
+   */
+  public function testDatastreamVersionDelete() {
+    $user = $this->drupalCreateUser(array(
+      'view old datastream versions',
+      'delete fedora objects and datastreams',
+    ));
+    $this->drupalLogin($user);
+    $this->drupalGet("islandora/object/{$this->pid}/datastream/{$this->dsid}/version");
+    $this->assertLink("delete");
+    $this->assertText('text/xml');
+
+    $encoded_pid = urlencode($this->pid);
+    $this->assertLinkByHref("islandora/object/$encoded_pid/datastream/{$this->dsid}/version/0/delete");
+    $this->assertLinkByHref("islandora/object/$encoded_pid/datastream/{$this->dsid}/version/1/delete");
+    $this->assertLinkByHref("islandora/object/$encoded_pid/datastream/{$this->dsid}/version/2/delete");
+    $this->assertLinkByHref("islandora/object/$encoded_pid/datastream/{$this->dsid}/version/3/delete");
+
+    $this->drupalGet("islandora/object/{$this->pid}/datastream/{$this->dsid}/version/3/delete");
+    $this->drupalPost(NULL, array(), t('Delete'));
+    $this->assertNoText('text/xml');
+  }
+
+  /**
+   * Make sure you can't delete versions that don't exist/have only 1 version.
+   */
+  public function testDatastreamVersionDeleteEdgeCase() {
+    $user = $this->drupalCreateUser(array(
+      'view old datastream versions',
+      'delete fedora objects and datastreams',
+    ));
+    $this->drupalLogin($user);
+
+    $this->drupalGet("islandora/object/{$this->pid}/datastream/{$this->dsid}/version/6/delete");
+    $this->assertResponse(404);
+
+    $this->drupalGet("islandora/object/{$this->pid}/datastream/DC/version/0/delete");
+    $this->assertResponse(404);
+  }
+}

theme/theme.inc

@@ -15,59 +15,71 @@ function islandora_preprocess_islandora_default_edit(array &$variables) {
   $variables['islandora_editmetadata_url'] = $base_url . '/islandora/edit_form/' . $islandora_object->id;
   module_load_include('inc', 'islandora', 'includes/datastream');
   module_load_include('inc', 'islandora', 'includes/utilities');
-  $header = array(
+  $header = array();
-    array('data' => t('ID')),
+  $header[] = array('data' => t('ID'));
-    array('data' => t('Label')),
+  $header[] = array('data' => t('Label'));
-    array('data' => t('Type')),
+  $header[] = array('data' => t('Type'));
-    array('data' => t('Mime type')),
+  $header[] = array('data' => t('Mime type'));
-    array('data' => t('Size')),
+  $header[] = array('data' => t('Size'));
-    array('data' => t('Operations'), 'colspan' => '3'),
+  if (user_access(ISLANDORA_VIEW_DATASTREAM_HISTORY)) {
-  );
+    $header[] = array('data' => t('Versions'));
+  }
+
+  $header[] = array('data' => t('Operations'), 'colspan' => '3');
+
   $table_attributes = array('class' => array('manage-datastreams'));
   $rows = array();
   foreach ($islandora_object as $ds) {
-    $rows[] = array(
+    $row = array();
-      array(
+    $row[] = array(
-        'class' => 'datastream-id',
+      'class' => 'datastream-id',
-        'data' => theme('islandora_datastream_view_link', array(
+      'data' => theme('islandora_datastream_view_link', array(
-          'datastream' => $ds,
+        'datastream' => $ds,
-        )),
+      )),
-      ),
+    );
-      array(
+    $row[] = array(
-        'class' => 'datastream-label',
+      'class' => 'datastream-label',
-        'data' => $ds->label,
+      'data' => $ds->label,
-      ),
+    );
-      array(
+    $row[] = array(
-        'class' => 'datastream-control',
+      'class' => 'datastream-control',
-        'data' => islandora_control_group_to_human_readable($ds->controlGroup),
+      'data' => islandora_control_group_to_human_readable($ds->controlGroup),
-      ),
+    );
-      array(
+    $row[] = array(
-        'class' => 'datastream-mime',
+      'class' => 'datastream-mime',
-        'data' => $ds->mimeType,
+      'data' => $ds->mimeType,
-      ),
+    );
-      array(
+    $row[] = array(
-        'class' => 'datastream-size',
+      'class' => 'datastream-size',
-        'data' => islandora_datastream_get_human_readable_size($ds),
+      'data' => islandora_datastream_get_human_readable_size($ds),
-      ),
+    );
-      array(
+    if (user_access(ISLANDORA_VIEW_DATASTREAM_HISTORY)) {
-        'class' => 'datastream-download',
+      $row[] = array(
-        'data' => theme('islandora_datastream_download_link', array(
+        'class' => 'datastream-versions',
-          'datastream' => $ds,
+        'data' => theme('islandora_datastream_version_link', array(
-        )),
-      ),
-      array(
-        'class' => 'datstream-edit',
-        'data' => theme('islandora_datastream_edit_link', array(
-          'datastream' => $ds,
-        )),
-      ),
-      array(
-        'class' => 'datastream-delete',
-        'data' => theme('islandora_datastream_delete_link', array(
           'datastream' => $ds,
         )),
-      ),
+      );
+    }
+    $row[] = array(
+      'class' => 'datastream-download',
+      'data' => theme('islandora_datastream_download_link', array(
+        'datastream' => $ds,
+      )),
+    );
+    $row[] = array(
+      'class' => 'datstream-edit',
+      'data' => theme('islandora_datastream_edit_link', array(
+        'datastream' => $ds,
+      )),
+    );
+    $row[] = array(
+      'class' => 'datastream-delete',
+      'data' => theme('islandora_datastream_delete_link', array(
+        'datastream' => $ds,
+      )),
     );
+    $rows[] = $row;
   }
   $caption = $islandora_object->label . ' - ' . $islandora_object->id;
   $table = array(
@@ -256,15 +268,33 @@ function theme_islandora_datastream_download_link(array $vars) {
  * @param array $vars
  *   An array containing:
  *   - datastream: An AbstractDatastream for which to generate a view link.
+ *   - label: (Optional) The label for the link.
+ *   - version: (Optional) The version of the datstream to link to.
  */
 function theme_islandora_datastream_view_link(array $vars) {
   $datastream = $vars['datastream'];
   module_load_include('inc', 'islandora', 'includes/utilities');
 
-  $label = check_plain($datastream->id);
+  if ($vars['label'] === NULL) {
-  return islandora_datastream_access(FEDORA_VIEW_OBJECTS, $datastream) ?
+    $label = check_plain($datastream->id);
-    l($label, islandora_datastream_get_url($datastream, 'view')) :
+  }
-    $label;
+  else {
+    $label = check_plain($vars['label']);
+  }
+
+  if ($vars['version'] === NULL) {
+    $perm = FEDORA_VIEW_OBJECTS;
+  }
+  else {
+    $perm = ISLANDORA_VIEW_DATASTREAM_HISTORY;
+  }
+
+  if (islandora_datastream_access($perm, $datastream)) {
+    return l($label, islandora_datastream_get_url($datastream, 'view', $vars['version']));
+  }
+  else {
+    return $label;
+  }
 }
 
 /**
@@ -273,6 +303,7 @@ function theme_islandora_datastream_view_link(array $vars) {
  * @param array $vars
  *   An array containing:
  *   - datastream: An AbstractDatastream for which to generate a delete link.
+ *   - version: (optional) the version of the datastream to delete.
  */
 function theme_islandora_datastream_delete_link(array $vars) {
   $datastream = $vars['datastream'];
@@ -281,9 +312,22 @@ function theme_islandora_datastream_delete_link(array $vars) {
 
   $can_delete = !in_array($datastream->id, $datastreams) && islandora_datastream_access(FEDORA_PURGE, $datastream);
 
-  return $can_delete ?
+  if ($vars['version'] !== NULL) {
-    l(t('delete'), "islandora/object/{$datastream->parent->id}/datastream/{$datastream->id}/delete") :
+    if (count($datastream) == 1) {
+      $can_delete = FALSE;
+    }
+    $link = "islandora/object/{$datastream->parent->id}/datastream/{$datastream->id}/version/{$vars['version']}/delete";
+  }
+  else {
+    $link = "islandora/object/{$datastream->parent->id}/datastream/{$datastream->id}/delete";
+  }
+
+  if ($can_delete) {
+    return l(t('delete'), $link);
+  }
+  else {
     '';
+  }
 }
 
 /**
@@ -304,3 +348,32 @@ function theme_islandora_datastream_edit_link(array $vars) {
     l(t('edit'), "islandora/object/{$datastream->parent->id}/datastream/{$datastream->id}/edit") :
     '';
 }
+
+/**
+ * Renders a link to take you to the datastream versions page.
+ *
+ * @param array $vars
+ *   An array containing:
+ *   - datastream: An AbstractDatastream to generate the version link from.
+ *
+ * @return string
+ *   Markup.
+ */
+function theme_islandora_datastream_version_link(array $vars) {
+  $datastream = $vars['datastream'];
+  module_load_include('inc', 'islandora', 'includes/utilities');
+
+  $see_history = islandora_datastream_access(ISLANDORA_VIEW_DATASTREAM_HISTORY, $datastream);
+
+  if ($see_history) {
+    if ($datastream->versionable) {
+      return l(count($datastream), "islandora/object/{$datastream->parent->id}/datastream/{$datastream->id}/version");
+    }
+    else {
+      return t('Not Versioned');
+    }
+  }
+  else {
+    return '';
+  }
+}