info_tren/lib/models/ui_timezone.dart

import 'package:timezone/timezone.dart' as tz;

enum UiTimeZoneType {
  ro,
  local,
  utc,
  iana,
}

extension UITimeZoneTypeName on UiTimeZoneType {
  String get userInterfaceName => (const {
    UiTimeZoneType.iana: 'Fus orar IANA',
    UiTimeZoneType.local: 'Local',
    UiTimeZoneType.ro: 'România',
    UiTimeZoneType.utc: 'UTC',
  })[this]!;
}

const Map<UiTimeZoneType, UiTimeZone Function(String)> fromSerStringConstructors = {
  UiTimeZoneType.ro: RoUiTimeZone.fromSerString,
  UiTimeZoneType.local: LocalUiTimeZone.fromSerString,
  UiTimeZoneType.utc: UtcUiTimeZone.fromSerString,
  UiTimeZoneType.iana: IanaUiTimeZone.fromSerString,
};

abstract class UiTimeZone {
  final UiTimeZoneType type;

  const UiTimeZone({required this.type});

  DateTime convertDateTime(DateTime dt);

  factory UiTimeZone.fromSerString(String ser) {
    final arr = ser.split('\n');
    return fromSerStringConstructors.map((key, value) => MapEntry(key.name, value))[arr[0]]!(ser);
  }

  String toSerString() {
    return '${type.name}\n';
  }
}

class RoUiTimeZone extends UiTimeZone {
  static final roTz = tz.getLocation('Europe/Bucharest');

  const RoUiTimeZone() : super(type: UiTimeZoneType.ro);

  factory RoUiTimeZone.fromSerString(String ser) => const RoUiTimeZone();

  @override
  DateTime convertDateTime(DateTime dt) {
    return tz.TZDateTime.from(dt, roTz);
  }
}

class LocalUiTimeZone extends UiTimeZone {
  const LocalUiTimeZone() : super(type: UiTimeZoneType.local);

  factory LocalUiTimeZone.fromSerString(String ser) => LocalUiTimeZone();

  @override
  DateTime convertDateTime(DateTime dt) => dt.toLocal();
}

class UtcUiTimeZone extends UiTimeZone {
  const UtcUiTimeZone() : super(type: UiTimeZoneType.utc);

  factory UtcUiTimeZone.fromSerString(String ser) => UtcUiTimeZone();

  @override
  DateTime convertDateTime(DateTime dt) => dt.toUtc();
}

class IanaUiTimeZone extends UiTimeZone {
  late final tz.Location location;

  IanaUiTimeZone({required String ianaName}): super(type: UiTimeZoneType.iana) {
    location = tz.getLocation(ianaName);
  }

  factory IanaUiTimeZone.fromSerString(String ser) => IanaUiTimeZone(
    ianaName: ser.split('\n').skip(1).join('\n'),
  );

  @override
  DateTime convertDateTime(DateTime dt) {
    return tz.TZDateTime.from(dt, location);
  }

  @override
  String toSerString() {
    return '${type.name}\n${location.name}';
  }
}