Move command classes to domain namespaces

They will probably be refactored away at a later stage (when we get
rid of the command bus). Until then, this lets us remove the
Flarum\Core namespace and actually feels quite clean.

src/Post/Command/DeletePostHandler.php

@@ -0,0 +1,63 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * (c) Toby Zerner <toby.zerner@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Flarum\Post\Command;
+
+use Flarum\Foundation\DispatchEventsTrait;
+use Flarum\Post\Event\Deleting;
+use Flarum\Post\PostRepository;
+use Flarum\User\AssertPermissionTrait;
+use Illuminate\Contracts\Events\Dispatcher;
+
+class DeletePostHandler
+{
+    use DispatchEventsTrait;
+    use AssertPermissionTrait;
+
+    /**
+     * @var \Flarum\Post\PostRepository
+     */
+    protected $posts;
+
+    /**
+     * @param Dispatcher $events
+     * @param \Flarum\Post\PostRepository $posts
+     */
+    public function __construct(Dispatcher $events, PostRepository $posts)
+    {
+        $this->events = $events;
+        $this->posts = $posts;
+    }
+
+    /**
+     * @param DeletePost $command
+     * @return \Flarum\Post\Post
+     * @throws \Flarum\User\Exception\PermissionDeniedException
+     */
+    public function handle(DeletePost $command)
+    {
+        $actor = $command->actor;
+
+        $post = $this->posts->findOrFail($command->postId, $actor);
+
+        $this->assertCan($actor, 'delete', $post);
+
+        $this->events->fire(
+            new Deleting($post, $actor, $command->data)
+        );
+
+        $post->delete();
+
+        $this->dispatchEventsFor($post, $actor);
+
+        return $post;
+    }
+}