class SystemMessage

class SystemMessage extends RulesActionBase implements ContainerFactoryPluginInterface {
  
  /**
   * The messenger service.
   *
   * @var \Drupal\Core\Messenger\MessengerInterface
   */
  protected $messenger;
  
  /**
   * Constructs a SystemMessage object.
   *
   * @param array $configuration
   *   A configuration array containing information about the plugin instance.
   * @param string $plugin_id
   *   The plugin ID for the plugin instance.
   * @param mixed $plugin_definition
   *   The plugin implementation definition.
   * @param \Drupal\Core\Messenger\MessengerInterface $messenger
   *   The messenger service.
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, MessengerInterface $messenger) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
    $this->messenger = $messenger;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static($configuration, $plugin_id, $plugin_definition, $container->get('messenger'));
  }
  
  /**
   * Set a system message.
   *
   * @param string $message
   *   Message string that should be set.
   * @param string $type
   *   Type of the message.
   * @param bool $repeat
   *   (optional) TRUE if the message should be repeated.
   */
  protected function doExecute($message, $type, $repeat) {
    // @todo Should we do the sanitization somewhere else? D7 had the sanitize
    // flag in the context definition.
    $message = Xss::filterAdmin($message);
    $repeat = (bool) $repeat;
    $this->messenger
      ->addMessage(Markup::create($message), $type, $repeat);
  }

}