interface MessengerInterface

interface MessengerInterface {
    
    /**
     * A status message.
     */
    const TYPE_STATUS = 'status';
    
    /**
     * A warning.
     */
    const TYPE_WARNING = 'warning';
    
    /**
     * An error.
     */
    const TYPE_ERROR = 'error';
    
    /**
     * Adds a new message to the queue.
     *
     * The messages will be displayed in the order they got added later.
     *
     * @param string|\Drupal\Component\Render\MarkupInterface $message
     *   (optional) The translated message to be displayed to the user. For
     *   consistency with other messages, it should begin with a capital letter
     *   and end with a period.
     * @param string $type
     *   (optional) The message's type. Either self::TYPE_STATUS,
     *   self::TYPE_WARNING, or self::TYPE_ERROR.
     * @param bool $repeat
     *   (optional) If this is FALSE and the message is already set, then the
     *   message won't be repeated. Defaults to FALSE.
     *
     * @return $this
     */
    public function addMessage($message, $type = self::TYPE_STATUS, $repeat = FALSE);
    
    /**
     * Adds a new status message to the queue.
     *
     * @param string|\Drupal\Component\Render\MarkupInterface $message
     *   (optional) The translated message to be displayed to the user. For
     *   consistency with other messages, it should begin with a capital letter
     *   and end with a period.
     * @param bool $repeat
     *   (optional) If this is FALSE and the message is already set, then the
     *   message won't be repeated. Defaults to FALSE.
     *
     * @return $this
     */
    public function addStatus($message, $repeat = FALSE);
    
    /**
     * Adds a new error message to the queue.
     *
     * @param string|\Drupal\Component\Render\MarkupInterface $message
     *   (optional) The translated message to be displayed to the user. For
     *   consistency with other messages, it should begin with a capital letter
     *   and end with a period.
     * @param bool $repeat
     *   (optional) If this is FALSE and the message is already set, then the
     *   message won't be repeated. Defaults to FALSE.
     *
     * @return $this
     */
    public function addError($message, $repeat = FALSE);
    
    /**
     * Adds a new warning message to the queue.
     *
     * @param string|\Drupal\Component\Render\MarkupInterface $message
     *   (optional) The translated message to be displayed to the user. For
     *   consistency with other messages, it should begin with a capital letter
     *   and end with a period.
     * @param bool $repeat
     *   (optional) If this is FALSE and the message is already set, then the
     *   message won't be repeated. Defaults to FALSE.
     *
     * @return $this
     */
    public function addWarning($message, $repeat = FALSE);
    
    /**
     * Gets all messages.
     *
     * @return string[][]|\Drupal\Component\Render\MarkupInterface[][]
     *   Keys are message types and values are indexed arrays of messages. Message
     *   types are either self::TYPE_STATUS, self::TYPE_WARNING, or
     *   self::TYPE_ERROR.
     */
    public function all();
    
    /**
     * Gets all messages of a certain type.
     *
     * @param string $type
     *   The messages' type. Either self::TYPE_STATUS, self::TYPE_WARNING,
     *   or self::TYPE_ERROR.
     *
     * @return string[]|\Drupal\Component\Render\MarkupInterface[]
     *   The messages of given type.
     */
    public function messagesByType($type);
    
    /**
     * Deletes all messages.
     *
     * @return string[]|\Drupal\Component\Render\MarkupInterface[]
     *   The deleted messages.
     */
    public function deleteAll();
    
    /**
     * Deletes all messages of a certain type.
     *
     * @param string $type
     *   The messages' type. Either self::TYPE_STATUS, self::TYPE_WARNING, or
     *   self::TYPE_ERROR.
     *
     * @return string[]|\Drupal\Component\Render\MarkupInterface[]
     *   The deleted messages of given type.
     */
    public function deleteByType($type);

}