[Dart] Game filter for question in StackOverFlow

game_filter.dart

/// https://stackoverflow.com/questions/64529394/flutter-dart-how-to-remove-excepted-element-in-list-in-map

class PlatformFilter {
  bool isSelected;
  int id;
  PlatformFilter(this.id, this.isSelected);
}

class Game {
  int id;
  //String name...
  List<Platform> platforms;
  Game(this.id, this.platforms);
  @override
  String toString() => 'gameId: $id, platforms:${platforms.namesString()}';
}

class Platform {
  String name;
  int id;
  //IconData icon;
  //Other view value...
  Platform(this.id, this.name);
}

extension on List<Platform> {
  String namesString() {
    String values = '[';
    this.asMap().forEach((index, element) => values +=
        (index != this.length - 1) ? element.name + ',' : element.name + ']');
    return values;
  }
}

Map<int, List<Game>> filtering() {
  List<PlatformFilter> filters = [
    PlatformFilter(1, true), //Xbox
    PlatformFilter(2, true), //Playstation
    PlatformFilter(3, true), //Switch
    PlatformFilter(4, false), //Android
    PlatformFilter(5, false), //Mac
    PlatformFilter(6, false), //Linux
  ];

  Map<int, List<Game>> data = {
    1: [
      Game(1, [
        Platform(1, 'Xbox'),
        Platform(2, 'Playstation'),
        Platform(3, 'Switch')
      ]),
      Game(2,
          [Platform(1, 'Xbox'), Platform(3, 'Switch'), Platform(4, 'Android')]),
      Game(3,
          [Platform(4, 'Android'), Platform(5, 'Mac'), Platform(6, 'Linux')]),
    ],
    2: [
      Game(4, [
        Platform(2, 'Playstation'),
        Platform(3, 'Switch'),
        Platform(4, 'Android')
      ]),
      Game(
          5, [Platform(1, 'Xbox'), Platform(4, 'Android'), Platform(5, 'Mac')]),
    ],
    3: [
      Game(6, [Platform(5, 'Mac')]),
    ],
    4: [
      Game(7, [Platform(5, 'Mac'), Platform(4, 'Android')]),
    ],
    5: [
      Game(8, [Platform(3, 'Switch')]),
    ],
  };

  Map<int, List<Game>> result = {};
  data.forEach((key, group) {
    group.asMap().forEach((index, game) {
      game.platforms.forEach((platform) {
        filters.forEach((element) {
          if (element.id == platform.id && element.isSelected) {
            result.putIfAbsent(key, () => List());
            if (!result[key].contains(game)) {
              result[key].add(game);
            }
          }
        });
      });
    });
  });

  return result;
}

void main() {
  var result = filtering();
  result.forEach((key, value) {
    print('$key:');
    value.forEach((element) => print('\t$element'));
  });
}