public function do_filter( $filter, $new_value, $old_value ) {

    $available_filters = $this->get_available_filters();

    if ( ! array_key_exists( $filter, $available_filters ) ) {
      return $new_value;
    }

    return call_user_func( $available_filters[ $filter ], $new_value, $old_value );

  }