class ConfigCacheTag

class ConfigCacheTag implements EventSubscriberInterface {
  
  /**
   * Constructs a ConfigCacheTag object.
   */
  public function __construct(protected ThemeHandlerInterface $themeHandler, protected CacheTagsInvalidatorInterface $cacheTagsInvalidator, protected Registry $themeRegistry) {
  }
  
  /**
   * Invalidate cache tags when particular system config objects are saved.
   *
   * @param \Drupal\Core\Config\ConfigCrudEvent $event
   *   The Event to process.
   */
  public function onSave(ConfigCrudEvent $event) {
    $config_name = $event->getConfig()
      ->getName();
    // Changing the site settings may mean a different route is selected for the
    // front page. Additionally a change to the site name or similar must
    // invalidate the render cache since this could be used anywhere.
    if ($config_name === 'system.site') {
      $this->cacheTagsInvalidator
        ->invalidateTags([
        'route_match',
        'rendered',
      ]);
    }
    // Theme configuration and global theme settings.
    if (in_array($config_name, [
      'system.theme',
      'system.theme.global',
    ], TRUE)) {
      $this->cacheTagsInvalidator
        ->invalidateTags([
        'rendered',
      ]);
    }
    // Library and template overrides potentially change for the default theme
    // when the admin theme is changed.
    if ($config_name === 'system.theme' && $event->isChanged('admin')) {
      $this->themeRegistry
        ->reset();
      $this->cacheTagsInvalidator
        ->invalidateTags([
        'library_info',
      ]);
    }
    // Theme-specific settings, check if this matches a theme settings
    // configuration object (THEME_NAME.settings), in that case, clear the
    // rendered cache tag.
    if (preg_match('/^([^\\.]*)\\.settings$/', $config_name, $matches)) {
      if ($this->themeHandler
        ->themeExists($matches[1])) {
        $this->cacheTagsInvalidator
          ->invalidateTags([
          'rendered',
        ]);
      }
    }
  }
  
  /**
   * {@inheritdoc}
   */
  public static function getSubscribedEvents() : array {
    $events[ConfigEvents::SAVE][] = [
      'onSave',
    ];
    return $events;
  }

}