Parameterized JsonConverter #1536

class UserProfile {

  @DateTimeLocalJsonConverter()
  final DateTime? birthdate;

  const UserProfile(this.birthdate);
} 

class DateTimeUtcJsonConverter extends JsonConverter<DateTime, String> {
  /// if true, utc to local conversion is disabled
  final bool disableFromUtc;

  /// if true, local to utc conversion is disabled
  final bool disableToUtc;

  const DateTimeUtcJsonConverter({this.disableFromUtc = false, this.disableToUtc = false});

  @override
  DateTime fromJson(String json) {
    if (disableFromUtc) return DateTime.parse(json);

    return DateTime.parse(json).toLocal();
  }

  @override
  String toJson(DateTime object) {
    if (disableToUtc) return object.toIso8601String();

    return object.toUtc().toIso8601String();
  }
}

const localDateTimeConverter = DateTimeUtcJsonConverter(disableToUtc: true);