extension AsValueListenable<T> on Stream<T> {
  /// Converts a [Stream] to a [ValueListenable]
  ///
  /// The internal [StreamSubscription] is cancelled when
  /// all listeners added to [ValueListenable] are removed.
  /// Keep this in mind as this could cause issues with
  /// single-subscription streams.
  ValueListenable<T> asValueListenable(T initialValue) {
    return _StreamValueListenable(this, initialValue);
  }
}

class _StreamValueListenable<T> extends ValueNotifier<T> {
  _StreamValueListenable(this.stream, T initialValue) : super(initialValue);

  final Stream<T> stream;

  StreamSubscription<T> subscription;

  @override
  void addListener(VoidCallback listener) {
    subscription ??= stream.listen((event) {
      value = event;
    });
    super.addListener(listener);
  }

  @override
  void removeListener(VoidCallback listener) {
    super.removeListener(listener);
    if (!hasListeners && subscription != null) {
      subscription.cancel();
      subscription = null;
    }
  }
}