public function actionIndex()
 {
     $request = Yii::$app->request;
     try {
         $query = $request->get('search-string', '');
         $query = HtmlPurifier::process($query);
         Yii::$app->view->title = 'Kết quả tìm kiếm cho ' . $query;
         Yii::$app->view->registerMetaTag(['name' => 'description', 'content' => 'Bluebee-UET.com - Kết quả tìm kiếm cho ' . $query]);
         Yii::$app->view->registerMetaTag(['property' => 'og:title', 'content' => 'Bluebee-UET.com - Kết quả tìm kiếm cho ' . $query]);
         Yii::$app->view->registerMetaTag(['property' => 'og:description', 'content' => 'Bluebee-UET.com - Kết quả tìm kiếm cho ' . $query]);
         Yii::$app->view->registerMetaTag(['property' => 'og:image', 'content' => 'http://bluebee-uet.com/img/logo.jpg']);
         $attr = $request->get('attr', '');
         switch ($attr) {
             case 'teacher':
                 $data = Teachers::searchTeachers(strtolower($query));
                 break;
             case 'document':
                 $data = Documents::searchDocuments(strtolower($query));
                 break;
             case 'subject':
                 $data = Subjects::searchSubjects(strtolower($query));
                 break;
             default:
                 $this->redirect('http://bluebee-uet.com');
                 break;
         }
         $data['attr'] = $attr;
         $data['query'] = $query;
         return $this->render('index', $data);
     } catch (Exception $ex) {
     }
 }