String extension to parse ISO8601 duration String to duration object.

string_x.dart

extension StringX on String {
  /// Creates a `Duration` object from an ISO8601 formatted string.
  ///
  /// This method parses out a subset of the ISO8601 duration format. As years
  /// and months are not of a set length this method does not support that. We
  /// are then left with support for weeks, days, hours, minutes and seconds.
  Duration get toDuration {
    if (!RegExp(
            r"^(-|\+)?P(?:([-+]?[0-9,.]*)Y)?(?:([-+]?[0-9,.]*)M)?(?:([-+]?[0-9,.]*)W)?(?:([-+]?[0-9,.]*)D)?(?:T(?:([-+]?[0-9,.]*)H)?(?:([-+]?[0-9,.]*)M)?(?:([-+]?[0-9,.]*)S)?)?$")
        .hasMatch(this)) {
      throw ArgumentError("String does not follow correct format");
    }

    final weeks = _parseTime(this, "W");
    final days = _parseTime(this, "D");
    final hours = _parseTime(this, "H");
    final minutes = _parseTime(this, "M");
    final seconds = _parseTime(this, "S");

    return Duration(
      days: days + (weeks * 7),
      hours: hours,
      minutes: minutes,
      seconds: seconds,
    );
  }

  /// Private helper method for extracting a time value from the ISO8601 string.
  int _parseTime(String duration, String timeUnit) {
    final timeMatch = RegExp(r"\d+" + timeUnit).firstMatch(duration);

    if (timeMatch == null) {
      return 0;
    }
    final timeString = timeMatch.group(0);
    return int.parse(timeString.substring(0, timeString.length - 1));
  }
}

print('P1Y4M3W2DT10H31M'.toDuration); // 562:04:00.000000