Add unsubscribe link to forum post emails

htdocs/interaction/forum/lib.php

@@ -400,6 +400,8 @@ class ActivityTypeInteractionForumNewPost extends ActivityTypePlugin {
             $user->message = ($post->subject ? $post->subject . "\n" . str_repeat('-', strlen($post->subject)) . "\n" : '')
                 . trim(html2text($post->body));
         }
+        $this->unsubscribename = $post->forumtitle;
+        $this->unsubscribeurl = get_config('wwwroot') . 'interaction/forum/view.php?id=' . $post->forumid;
     }
 
     public function get_subject($user) {

htdocs/notification/email/lang/en.utf8/notification.email.php

@@ -30,6 +30,7 @@ $string['emailsubject'] = '%s';
 $string['emailheader'] = 'You have been sent a notification from %s. Message follows:';
 $string['emailfooter'] = 'This is an auto generated notification from %s. To update your notification preferences, visit %s';
 $string['referurl'] = 'See %s';
+$string['unsubscribemessage'] = "To unsubscribe from %s, visit\n%s";
 
 $string['name'] = 'Email';
 ?>

htdocs/notification/email/lib.php

@@ -57,6 +57,10 @@ class PluginNotificationEmail extends PluginNotification {
             }
         }
 
+        if (isset($data->unsubscribeurl) && isset($data->unsubscribename)) {
+            $messagebody .= "\n\n" . get_string_from_language($lang, 'unsubscribemessage', 'notification.email', $data->unsubscribename, $data->unsubscribeurl);
+        }
+
         $messagebody .= "\n\n$separator";
 
         $prefurl = get_config('wwwroot') . 'account/activity/preferences/';