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

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

  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:${_formatDateTime(dtstamp)}');
      buffer.writeln('DTSTART:${_formatDateTime(event.startTime)}');
      buffer.writeln('DTEND:${_formatDateTime(event.endTime)}');
      buffer.writeln('SUMMARY:${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';
  }
}

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

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