Started addition of favourite system

app/Actions/Favourite.php

@@ -0,0 +1,17 @@
+<?php namespace BookStack\Actions;
+
+use BookStack\Model;
+use Illuminate\Database\Eloquent\Relations\MorphTo;
+
+class Favourite extends Model
+{
+    protected $fillable = ['user_id'];
+
+    /**
+     * Get the related model that can be favourited.
+     */
+    public function favouritable(): MorphTo
+    {
+        return $this->morphTo();
+    }
+}

app/Actions/View.php

@@ -1,6 +1,7 @@
 <?php namespace BookStack\Actions;
 
 use BookStack\Model;
+use Illuminate\Database\Eloquent\Relations\MorphTo;
 
 class View extends Model
 {
@@ -9,9 +10,8 @@ class View extends Model
 
     /**
      * Get all owning viewable models.
-     * @return \Illuminate\Database\Eloquent\Relations\MorphTo
      */
-    public function viewable()
+    public function viewable(): MorphTo
     {
         return $this->morphTo();
     }

app/Entities/Models/Entity.php

@@ -2,6 +2,7 @@
 
 use BookStack\Actions\Activity;
 use BookStack\Actions\Comment;
+use BookStack\Actions\Favourite;
 use BookStack\Actions\Tag;
 use BookStack\Actions\View;
 use BookStack\Auth\Permissions\EntityPermission;
@@ -9,6 +10,7 @@ use BookStack\Auth\Permissions\JointPermission;
 use BookStack\Entities\Tools\SearchIndex;
 use BookStack\Entities\Tools\SlugGenerator;
 use BookStack\Facades\Permissions;
+use BookStack\Interfaces\Favouritable;
 use BookStack\Interfaces\Sluggable;
 use BookStack\Model;
 use BookStack\Traits\HasCreatorAndUpdater;
@@ -38,7 +40,7 @@ use Illuminate\Database\Eloquent\SoftDeletes;
  * @method static Builder withLastView()
  * @method static Builder withViewCount()
  */
-abstract class Entity extends Model implements Sluggable
+abstract class Entity extends Model implements Sluggable, Favouritable
 {
     use SoftDeletes;
     use HasCreatorAndUpdater;
@@ -297,4 +299,22 @@ abstract class Entity extends Model implements Sluggable
         $this->slug = app(SlugGenerator::class)->generate($this);
         return $this->slug;
     }
+
+    /**
+     * @inheritdoc
+     */
+    public function favourites(): MorphMany
+    {
+        return $this->morphMany(Favourite::class, 'favouritable');
+    }
+
+    /**
+     * Check if the entity is a favourite of the current user.
+     */
+    public function isFavourite(): bool
+    {
+        return $this->favourites()
+            ->where('user_id', '=', user()->id)
+            ->exists();
+    }
 }

app/Http/Controllers/FavouriteController.php

@@ -0,0 +1,76 @@
+<?php
+
+namespace BookStack\Http\Controllers;
+
+use BookStack\Entities\Models\Entity;
+use BookStack\Interfaces\Favouritable;
+use BookStack\Model;
+use Illuminate\Http\Request;
+
+class FavouriteController extends Controller
+{
+    /**
+     * Add a new item as a favourite.
+     */
+    public function add(Request $request)
+    {
+        $favouritable = $this->getValidatedModelFromRequest($request);
+        $favouritable->favourites()->firstOrCreate([
+            'user_id' => user()->id,
+        ]);
+
+        $this->showSuccessNotification(trans('activities.favourite_add_notification', [
+            'name' => $favouritable->name,
+        ]));
+        return redirect()->back();
+    }
+
+    /**
+     * Remove an item as a favourite.
+     */
+    public function remove(Request $request)
+    {
+        $favouritable = $this->getValidatedModelFromRequest($request);
+        $favouritable->favourites()->where([
+            'user_id' => user()->id,
+        ])->delete();
+
+        $this->showSuccessNotification(trans('activities.favourite_remove_notification', [
+            'name' => $favouritable->name,
+        ]));
+        return redirect()->back();
+    }
+
+    /**
+     * @throws \Illuminate\Validation\ValidationException
+     * @throws \Exception
+     */
+    protected function getValidatedModelFromRequest(Request $request): Favouritable
+    {
+        $modelInfo = $this->validate($request, [
+            'type' => 'required|string',
+            'id' => 'required|integer',
+        ]);
+
+        if (!class_exists($modelInfo['type'])) {
+            throw new \Exception('Model not found');
+        }
+
+        /** @var Model $model */
+        $model = new $modelInfo['type'];
+        if (! $model instanceof Favouritable) {
+            throw new \Exception('Model not favouritable');
+        }
+
+        $modelInstance = $model->newQuery()
+            ->where('id', '=', $modelInfo['id'])
+            ->first(['id', 'name']);
+
+        $inaccessibleEntity = ($modelInstance instanceof Entity && !userCan('view', $modelInstance));
+        if (is_null($modelInstance) || $inaccessibleEntity) {
+            throw new \Exception('Model instance not found');
+        }
+
+        return $modelInstance;
+    }
+}

app/Interfaces/Favouritable.php

@@ -0,0 +1,11 @@
+<?php namespace BookStack\Interfaces;
+
+use Illuminate\Database\Eloquent\Relations\MorphMany;
+
+interface Favouritable
+{
+    /**
+     * Get the related favourite instances.
+     */
+    public function favourites(): MorphMany;
+}