Make breadcrumb creation a hookable process.

includes/breadcrumb.inc

@@ -25,9 +25,20 @@
  *   drupal_set_breadcrumb().
  */
 function islandora_get_breadcrumbs($object) {
-  $breadcrumbs = array();
+
   if (variable_get('islandora_render_drupal_breadcrumbs', TRUE)) {
-    $breadcrumbs = islandora_get_breadcrumbs_recursive($object->id, $object->repository);
+    $backend = variable_get('islandora_breadcrumbs_backends', ISLANDORA_BREADCRUMB_LEGACY_BACKEND);
+    $backends = module_invoke_all('islandora_breadcrumbs_backends');
+    if ($backend === ISLANDORA_BREADCRUMB_LEGACY_BACKEND || !isset($backends[$backend])) {
+      $breadcrumbs = islandora_get_breadcrumbs_recursive($object->id, $object->repository);
+    }
+    else {
+      if (isset($backends[$backend]['file'])) {
+        require_once $backends[$backend]['file'];
+      }
+      $breadcrumbs = call_user_func($backends[$backend]['callable'], $object);
+    }
+    
     array_pop($breadcrumbs);
     $context = 'islandora';
     drupal_alter('islandora_breadcrumbs', $breadcrumbs, $context, $object);

islandora.api.php

@@ -907,3 +907,43 @@ function hook_islandora_edit_datastream_registry_alter(&$edit_registry, $context
 function hook_islandora_repository_connection_construction_alter(RepositoryConnection $instance) {
   $instance->userAgent = "Tuque/cURL";
 }
+
+/**
+ * Allow a overridable backend for generating breadcrumbs.
+ *
+ * Stolen shamelessly from @adam-vessey
+ *
+ * @return array
+ *   Should return an associative array mapping unique (module-prefixed,
+ *   preferably) keys to associative arrays containing:
+ *   - title: A human-readable title for the backend.
+ *   - callable: A PHP callable to call for this backend, implementing
+ *     callback_islandora_basic_collection_query_backends().
+ *   - file: An optional file to load before attempting to call the callable.
+ */
+function hook_islandora_breadcrumbs_backends() {
+  $a_callable = function ($object) {
+    // Do something to get an array of breadcrumb links for $object, root first.
+    return array($root_link, $collection_link, $object_link);
+  };
+  return array(
+    'awesome_backend' => array(
+      'title' => t('Awesome Backend'),
+      'callable' => $a_callable,
+    ),
+  );
+}
+
+/**
+ * Generate an array of links for breadcrumbs leading to $object, root level first.
+ *
+ * @param AbstractObject $object
+ *   The object to generate breadcrumbs for
+ *
+ * @return array
+ *   Array of links from root to $object.
+ */
+function callback_islandora_breadcrumbs_backends(AbstractObject $object) {
+  // Do something to get an array of breadcrumb links for $object, root first.
+  return array($root_link, $collection_link, $object_link);
+}

islandora.module

@@ -68,6 +68,8 @@ define('ISLANDORA_DERIVATIVE_CREATION_HOOK', 'islandora_derivative');
 define('ISLANDORA_CONTENT_MODELS_AUTOCOMPLETE', 'islandora/autocomplete/content-models');
 define('ISLANDORA_MIME_TYPES_AUTOCOMPLETE', 'islandora/autocomplete/mime-types');
 
+const ISLANDORA_BREADCRUMB_LEGACY_BACKEND = 'islandora_breadcrumbs_legacy_sparql';
+
 /**
  * Implements hook_menu().
  *
@@ -2171,3 +2173,17 @@ function islandora_create_manage_overview(AbstractObject $object) {
   $output = theme('islandora_object_overview', array('islandora_object' => $object));
   return array('cmodels' => $output);
 }
+
+/**
+ * Implements hook_islandora_breadcrumbs_backends().
+ */
+function islandora_islandora_breadcrumbs_backends() {
+  $module_path = drupal_get_path('module', 'islandora');
+  return array(
+    ISLANDORA_BREADCRUMB_LEGACY_BACKEND => array(
+      'title' => t('Resource Index - Default'),
+      // Callback not needed as this is our legacy process and the
+      // default incase anything goes wrong.
+    ),
+  );
+}