Input WYSIWYG: Added reference store & fetch handling

For book, shelves and chapters.
Made much of the existing handling generic to entity types.
Added new MixedEntityListLoader to help load lists somewhat efficiently.
Only manually tested so far.

app/References/ReferenceFetcher.php

@@ -3,65 +3,51 @@
 namespace BookStack\References;
 
 use BookStack\Entities\Models\Entity;
-use BookStack\Entities\Models\Page;
+use BookStack\Entities\Tools\MixedEntityListLoader;
 use BookStack\Permissions\PermissionApplicator;
 use Illuminate\Database\Eloquent\Builder;
 use Illuminate\Database\Eloquent\Collection;
-use Illuminate\Database\Eloquent\Relations\Relation;
 
 class ReferenceFetcher
 {
-    protected PermissionApplicator $permissions;
-
-    public function __construct(PermissionApplicator $permissions)
-    {
-        $this->permissions = $permissions;
+    public function __construct(
+        protected PermissionApplicator $permissions,
+        protected MixedEntityListLoader $mixedEntityListLoader,
+    ) {
     }
 
     /**
-     * Query and return the page references pointing to the given entity.
+     * Query and return the references pointing to the given entity.
      * Loads the commonly required relations while taking permissions into account.
      */
-    public function getPageReferencesToEntity(Entity $entity): Collection
+    public function getReferencesToEntity(Entity $entity): Collection
     {
-        $baseQuery = $this->queryPageReferencesToEntity($entity)
-            ->with([
-                'from'         => fn (Relation $query) => $query->select(Page::$listAttributes),
-                'from.book'    => fn (Relation $query) => $query->scopes('visible'),
-                'from.chapter' => fn (Relation $query) => $query->scopes('visible'),
-            ]);
-
-        $references = $this->permissions->restrictEntityRelationQuery(
-            $baseQuery,
-            'references',
-            'from_id',
-            'from_type'
-        )->get();
+        $references = $this->queryReferencesToEntity($entity)->get();
+        $this->mixedEntityListLoader->loadIntoRelations($references->all(), 'from');
 
         return $references;
     }
 
     /**
-     * Returns the count of page references pointing to the given entity.
+     * Returns the count of references pointing to the given entity.
      * Takes permissions into account.
      */
-    public function getPageReferenceCountToEntity(Entity $entity): int
+    public function getReferenceCountToEntity(Entity $entity): int
     {
-        $count = $this->permissions->restrictEntityRelationQuery(
-            $this->queryPageReferencesToEntity($entity),
+        return $this->queryReferencesToEntity($entity)->count();
+    }
+
+    protected function queryReferencesToEntity(Entity $entity): Builder
+    {
+        $baseQuery = Reference::query()
+            ->where('to_type', '=', $entity->getMorphClass())
+            ->where('to_id', '=', $entity->id);
+
+        return $this->permissions->restrictEntityRelationQuery(
+            $baseQuery,
             'references',
             'from_id',
             'from_type'
-        )->count();
-
-        return $count;
-    }
-
-    protected function queryPageReferencesToEntity(Entity $entity): Builder
-    {
-        return Reference::query()
-            ->where('to_type', '=', $entity->getMorphClass())
-            ->where('to_id', '=', $entity->id)
-            ->where('from_type', '=', (new Page())->getMorphClass());
+        );
     }
 }