class Messenger

class Messenger implements MessengerInterface {
    
    /**
     * The flash bag.
     *
     * @var \Symfony\Component\HttpFoundation\Session\Flash\FlashBagInterface
     */
    protected $flashBag;
    
    /**
     * The kill switch.
     *
     * @var \Drupal\Core\PageCache\ResponsePolicy\KillSwitch
     */
    protected $killSwitch;
    
    /**
     * Messenger constructor.
     *
     * @param \Symfony\Component\HttpFoundation\Session\Flash\FlashBagInterface $flash_bag
     *   The flash bag.
     * @param \Drupal\Core\PageCache\ResponsePolicy\KillSwitch $killSwitch
     *   The kill switch.
     */
    public function __construct(FlashBagInterface $flash_bag, KillSwitch $killSwitch) {
        $this->flashBag = $flash_bag;
        $this->killSwitch = $killSwitch;
    }
    
    /**
     * {@inheritdoc}
     */
    public function addError($message, $repeat = FALSE) {
        return $this->addMessage($message, static::TYPE_ERROR, $repeat);
    }
    
    /**
     * {@inheritdoc}
     */
    public function addMessage($message, $type = self::TYPE_STATUS, $repeat = FALSE) {
        if (!$message instanceof Markup && $message instanceof MarkupInterface) {
            $message = Markup::create((string) $message);
        }
        // Do not use strict type checking so that equivalent string and
        // MarkupInterface objects are detected.
        if ($repeat || !in_array($message, $this->flashBag
            ->peek($type))) {
            $this->flashBag
                ->add($type, $message);
        }
        // Mark this page as being uncacheable.
        $this->killSwitch
            ->trigger();
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function addStatus($message, $repeat = FALSE) {
        return $this->addMessage($message, static::TYPE_STATUS, $repeat);
    }
    
    /**
     * {@inheritdoc}
     */
    public function addWarning($message, $repeat = FALSE) {
        return $this->addMessage($message, static::TYPE_WARNING, $repeat);
    }
    
    /**
     * {@inheritdoc}
     */
    public function all() {
        return $this->flashBag
            ->peekAll();
    }
    
    /**
     * {@inheritdoc}
     */
    public function deleteAll() {
        return $this->flashBag
            ->clear();
    }
    
    /**
     * {@inheritdoc}
     */
    public function deleteByType($type) {
        // Flash bag gets and clears flash messages from the stack.
        return $this->flashBag
            ->get($type);
    }
    
    /**
     * {@inheritdoc}
     */
    public function messagesByType($type) {
        return $this->flashBag
            ->peek($type);
    }

}