opencafe / datium

   * @param $value string

   * @return object

   */

  public function add( $value ) {

    $this->date_interval_expression = str_replace( $this->config['date_simple'], $this->config['date_interval'], $value );

    $this->date_interval_expression = str_replace( ' ', '', 'P' . $this->date_interval_expression );

    $this->date_time->add( new DateInterval( $this->date_interval_expression ) );

    return $this;

  }

  /**

   * Sub date from current date

   * @param $value

   * @return obejct

   */

  public function sub( $value ) {

    $this->date_interval_expression = str_replace( $this->config['date_simple'], $this->config['date_interval'], $value );

    $this->date_interval_expression = str_replace( ' ', '', 'P' . $this->date_interval_expression );

    $this->date_time->sub( new DateInterval( $this->date_interval_expression ) );

    return $this;

  }

  /**

   * Check if current year is leap or not