[CORE][EXTENSIONS] Added extension (modules, plugins) loading and test plugin, which is able to handle events

src/Util/ExtensionManager.php

@@ -0,0 +1,33 @@
+<?php
+
+namespace App\Util;
+
+use App\Util\GSEvent as Event;
+use Functional as F;
+
+abstract class ExtensionManager
+{
+    public static array $extensions = [];
+
+    public static function loadExtensions()
+    {
+        $plugins_paths = glob(INSTALLDIR . '/plugins/enabled/*');
+
+        foreach ($plugins_paths as $plugin_path) {
+            $class_name = basename($plugin_path);
+            $qualified  = 'Plugin\\' . $class_name . '\\' . $class_name;
+
+            require_once $plugin_path . '/' . $class_name . '.php';
+            $class              = new $qualified;
+            self::$extensions[] = $class;
+
+            // Register event handlers
+            $methods = get_class_methods($class);
+            $events  = F\select($methods, Common::swapArgs('startsWith', 'on'));
+            F\map($events,
+                  function (string $m) use ($class) {
+                      Event::addHandler(substr($m, 2), [$class, $m]);
+                  });
+        }
+    }
+}