Backport TReactionUserNotificationEvent to version 3.0

This backport ensures the compatibility for version 3.0 (and above) and version 5.2. With this commit, plugins can fully support the reaction system and the like system, previously this was only possible to a limited extent.
See #2508

diff --git a/wcfsetup/install/files/lib/system/user/notification/event/TReactionUserNotificationEvent.class.php b/wcfsetup/install/files/lib/system/user/notification/event/TReactionUserNotificationEvent.class.php
new file mode 100644 (file)
index 0000000..7f138d7
--- /dev/null
+++ b/wcfsetup/install/files/lib/system/user/notification/event/TReactionUserNotificationEvent.class.php
@@ -0,0 +1,56 @@
+<?php
+namespace wcf\system\user\notification\event;
+use wcf\data\user\UserProfile;
+use wcf\system\user\notification\object\IUserNotificationObject;
+
+/**
+ * This trait can be used in likeable user notification events to determine the reactionType counts
+ * for a specific user notification object.
+ * 
+ * HEADS UP: This trait is only included in version 3.0 and 3.1 for compatibility reasons. The method 
+ * getReactionsForAuthors() throws a \BadMethodCallException exception, if it used in version 3.0 or 3.1.
+ *
+ * @author     Joshua Ruesweg
+ * @copyright  2001-2019 WoltLab GmbH
+ * @license    GNU Lesser General Public License <http://opensource.org/licenses/lgpl-license.php>
+ * @package    WoltLabSuite\Core\System\User\Notification\Event
+ * @since      3.0
+ */
+trait TReactionUserNotificationEvent {
+       /**
+        * Cached reactions
+        * @var int[]
+        */
+       private $cachedReactions;
+       
+       /**
+        * Returns the count of reactionTypeIDs for the specific user notification object.
+        *
+        * @return      int[]
+        * @throws      \BadMethodCallException
+        */
+       protected final function getReactionsForAuthors() {
+               throw new \BadMethodCallException("The method is only supported from version 5.2 and only available for compatibility reasons.");
+       }
+       
+       /**
+        * Returns the author for this notification event.
+        *
+        * @return      UserProfile
+        */
+       abstract public function getAuthor();
+       
+       /**
+        * Returns a list of authors for stacked notifications sorted by time.
+        *
+        * @return      UserProfile[]
+        */
+       abstract public function getAuthors();
+       
+       /**
+        * Returns the underlying user notification object.
+        *
+        * @return      IUserNotificationObject
+        */
+       abstract public function getUserNotificationObject();
+}