Add setting to automatically follow after reply. closes flarum/core#310

extensions/subscriptions/src/Listener/FollowAfterReply.php

@@ -0,0 +1,55 @@
+<?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\Subscriptions\Listener;
+
+use Flarum\Core\Access\AssertPermissionTrait;
+use Flarum\Event\ConfigureUserPreferences;
+use Flarum\Event\PostWasPosted;
+use Illuminate\Contracts\Events\Dispatcher;
+
+class FollowAfterReply
+{
+    use AssertPermissionTrait;
+
+    /**
+     * @param Dispatcher $events
+     */
+    public function subscribe(Dispatcher $events)
+    {
+        $events->listen(ConfigureUserPreferences::class, [$this, 'addUserPreference']);
+        $events->listen(PostWasPosted::class, [$this, 'whenPostWasPosted']);
+    }
+
+    /**
+     * @param ConfigureUserPreferences $event
+     */
+    public function addUserPreference(ConfigureUserPreferences $event)
+    {
+        $event->add('followAfterReply', 'boolval', false);
+    }
+
+    /**
+     * @param PostWasPosted $event
+     */
+    public function whenPostWasPosted(PostWasPosted $event)
+    {
+        $actor = $event->actor;
+
+        if ($actor && $actor->exists && $actor->getPreference('followAfterReply')) {
+            $this->assertRegistered($actor);
+
+            $state = $event->post->discussion->stateFor($actor);
+
+            $state->subscription = 'follow';
+            $state->save();
+        }
+    }
+}