class ThemeInfoRebuildSubscriber

class ThemeInfoRebuildSubscriber implements EventSubscriberInterface {
  use StringTranslationTrait;
  
  /**
   * Internal flag for handle user notification.
   */
  protected string $notificationFlag = 'devel.rebuild_theme_warning';
  
  /**
   * The devel config.
   */
  protected Config $config;
  
  /**
   * The current user.
   */
  protected AccountProxyInterface $account;
  
  /**
   * The theme handler.
   */
  protected ThemeHandlerInterface $themeHandler;
  
  /**
   * The messenger.
   */
  protected MessengerInterface $messenger;
  
  /**
   * The theme registry.
   */
  protected Registry $themeRegistry;
  
  /**
   * Constructs a ThemeInfoRebuildSubscriber object.
   *
   * @param \Drupal\Core\Config\ConfigFactoryInterface $config
   *   The config factory.
   * @param \Drupal\Core\Session\AccountProxyInterface $account
   *   The current user.
   * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
   *   The theme handler.
   * @param \Drupal\Core\Messenger\MessengerInterface $messenger
   *   The messenger.
   * @param \Drupal\Core\StringTranslation\TranslationInterface $string_translation
   *   The translation manager.
   * @param \Drupal\Core\Theme\Registry $theme_registry
   *   The theme registry.
   */
  public function __construct(ConfigFactoryInterface $config, AccountProxyInterface $account, ThemeHandlerInterface $theme_handler, MessengerInterface $messenger, TranslationInterface $string_translation, Registry $theme_registry) {
    $this->config = $config->get('devel.settings');
    $this->account = $account;
    $this->themeHandler = $theme_handler;
    $this->messenger = $messenger;
    $this->stringTranslation = $string_translation;
    $this->themeRegistry = $theme_registry;
  }
  
  /**
   * Forces the system to rebuild the theme registry.
   *
   * @param \Symfony\Component\HttpKernel\Event\RequestEvent $event
   *   The event to process.
   */
  public function rebuildThemeInfo(RequestEvent $event) : void {
    if ($this->config
      ->get('rebuild_theme')) {
      // Update the theme registry.
      $this->themeRegistry
        ->reset();
      // Refresh theme data.
      $this->themeHandler
        ->refreshInfo();
      // Resets the internal state of the theme handler and clear the 'system
      // list' cache; this allow to properly register, if needed, PSR-4
      // namespaces for theme extensions after refreshing the info data.
      $this->themeHandler
        ->reset();
      // Notify the user that the theme info are rebuilt on every request.
      $this->triggerWarningIfNeeded($event->getRequest());
    }
  }
  
  /**
   * Notifies the user that the theme info are rebuilt on every request.
   *
   * The warning message is shown only to users with adequate permissions and
   * only once per session.
   *
   * @param \Symfony\Component\HttpFoundation\Request $request
   *   The request.
   */
  protected function triggerWarningIfNeeded(Request $request) {
    if ($this->account
      ->hasPermission('access devel information')) {
      $session = $request->getSession();
      if (!$session->has($this->notificationFlag)) {
        $session->set($this->notificationFlag, TRUE);
        $message = $this->t('The theme information is being rebuilt on every request. Remember to <a href=":url">turn off</a> this feature on production websites.', [
          ':url' => Url::fromRoute('devel.admin_settings')->toString(),
        ]);
        $this->messenger
          ->addWarning($message);
      }
    }
  }
  
  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents() : array {
    // Set high priority value to start as early as possible.
    $events[KernelEvents::REQUEST][] = [
      'rebuildThemeInfo',
      256,
    ];
    return $events;
  }

}