ApplicationBooter: Add support for Event Subscribers registration

ApplicationBooter.php

@@ -5,7 +5,8 @@
 use Concrete\Core\Application\Application;
 use Concrete\Core\Routing\RouteListInterface;
 use Concrete\Core\Support\Facade\Route;
-use RuntimeException;
+use Symfony\Component\EventDispatcher\EventDispatcherInterface;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
 
 abstract class ApplicationBooter
 {
@@ -17,17 +18,17 @@ private function __construct()
     }
 
     /**
+     * Boot up Application.
+     *
      * @param Application $app
      *
-     * @throws RuntimeException
      * @noinspection PhpDocMissingThrowsInspection
      */
     final public static function boot(Application $app): void
     {
         static::_boot($app);
 
-        $routeListClasses = static::getRoutesClasses();
-        if ($routeListClasses !== []) {
+        if (($routeListClasses = static::getRoutesClasses()) !== []) {
             /**
              * @var \Concrete\Core\Routing\Router $router
              */
@@ -37,21 +38,49 @@ final public static function boot(Application $app): void
                     /** @noinspection PhpUnhandledExceptionInspection */
                     $router->loadRouteList($app->build($routeListClass));
                 } else {
-                    throw new RuntimeException(t(static::class . ':getRoutesClass: RoutesClass should be instanceof Concrete\Core\Routing\RouteListInterface'));
+                    self::throwInvalidClassRuntimeException('getRoutesClass', $routeListClass, RouteListInterface::class);
+                }
+            }
+        }
+
+        // Register Event Subscribers
+        if (($evtSubscriberClasses = static::getEventSubscribers()) !== []) {
+            $director = $app->make(EventDispatcherInterface::class);
+            foreach ($evtSubscriberClasses as $evtSubscriberClass) {
+                if (is_subclass_of($evtSubscriberClass, EventSubscriberInterface::class)) {
+                    /** @noinspection PhpUnhandledExceptionInspection */
+                    $director->addSubscriber($app->build($evtSubscriberClass));
+                } else {
+                    self::throwInvalidClassRuntimeException('getEventSubscribers', $evtSubscriberClass, EventSubscriberInterface::class);
                 }
             }
         }
     }
 
+    private static function throwInvalidClassRuntimeException(string $relatedMethod, $targetClass, string $requiredClass): void
+    {
+        throw new \RuntimeException(t('%s:%s - `%s` should be an instance of `%s`', static::class, $relatedMethod, (string) $targetClass, $requiredClass));
+    }
+
     abstract protected static function _boot(Application $app): void;
 
     /**
      * Get Class name for RouteList, must be instance of \Concrete\Core\Routing\RouteListInterface.
      *
-     * @return array
+     * @return string[]
      */
     protected static function getRoutesClasses(): array
     {
         return [];
     }
+
+    /**
+     * Event Subscribers should be instance of \Symfony\Component\EventDispatcher\EventSubscriberInterface.
+     *
+     * @return string[]
+     */
+    protected static function getEventSubscribers(): array
+    {
+        return [];
+    }
 }