/**
  * generate access token & refresh token
  * @return json access token
  */
 public function getToken()
 {
     $client = $this->GoogleApiManager->getClient();
     $client->authenticate($_GET['code']);
     $access_token = $client->getAccessToken();
     return $access_token;
 }
 /**
  * delete file
  * @param  string $file_id
  * @return mixed          
  */
 public function delete($file_id)
 {
     $result = $this->GoogleApiManager->delete($file_id);
     if ($result === 'success') {
         return redirect()->route('list_files')->with('flash_success', 'Deleted successfully');
     } else {
         return redirect()->route('list_files')->with('flash_error', $result);
     }
 }