class ICalendar {
  final List<ICalendarEvent> _events = [];

  void addEvent(
      {required String summary,
      required String description,
      required DateTime startTime,
      required DateTime endTime,
      required List<dynamic> attendees,
      bool allday = false}) {
    _events.add(
      ICalendarEvent(
          summary: summary,
          description: description,
          startTime: startTime,
          endTime: endTime,
          attendees: attendees,
          allday: allday),
    );
  }

  String serialize() {
    final dtstamp = DateTime.now();
    final buffer = StringBuffer();
    buffer.writeln('BEGIN:VCALENDAR');
    buffer.writeln('VERSION:2.0');
    buffer.writeln('PRODID:-//Your Organization//Your Product//EN');

    for (final event in _events) {
      buffer.writeln('BEGIN:VEVENT');
      buffer.writeln(
          'UID:${DateTime.now().millisecondsSinceEpoch}-${event.hashCode}');
      buffer.writeln('DTSTAMP:${_formatDateTime(dtstamp)}');
      buffer.writeln(
          'DTSTART:${event.allday ? _formatDate(event.startTime) : _formatDateTime(event.startTime)}');
      buffer.writeln(
          'DTEND:${event.allday ? _formatDate(event.startTime.add(Duration(days: 1))) : _formatDateTime(event.endTime)}');
      buffer.writeln('SUMMARY:${event.summary}');
      buffer.writeln('DESCRIPTION:${event.description}');

      for (final attendee in event.attendees) {
        buffer.writeln(
            'ATTENDEE;CN="${attendee.toString()}";ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:test@me.com');
      }

      buffer.writeln('END:VEVENT');
    }

    buffer.writeln('END:VCALENDAR');
    return buffer.toString();
  }

  String _formatDateTime(DateTime dt) {
    return '${dt.toUtc().toString().replaceAll('-', '').replaceAll(':', '').replaceAll(' ', 'T').split('.')[0]}Z';
  }

  String _formatDate(DateTime dateTime) {
    // Extract year, month, and day from the DateTime object
    String year = dateTime.year.toString().padLeft(4, '0');
    String month = dateTime.month.toString().padLeft(2, '0');
    String day = dateTime.day.toString().padLeft(2, '0');

    // Combine into the YYYYMMDD format
    return '$year$month$day';
  }
}

class ICalendarEvent {
  final String summary;
  final String description;
  final DateTime startTime;
  final DateTime endTime;
  final List<dynamic> attendees;
  final bool allday;

  ICalendarEvent({
    required this.summary,
    required this.description,
    required this.startTime,
    required this.endTime,
    required this.attendees,
    this.allday = false,
  });
}