import 'dart:async';

/// 自定义实现，替代已停维的 `countdown` 包的 [CountDown]。
///
/// 用法与原包兼容：
/// ```dart
/// var listener = CountDown(Duration(seconds: 90)).stream.listen(null);
/// listener.onData((Duration d) { ... d.inSeconds ... });
/// listener.onDone(() { ... });
/// ```
///
/// `stream` 每秒发出剩余 [Duration]（从满时长倒数到 0），到达 0 后关闭。
class CountDown {
  CountDown(this.duration) : assert(!duration.isNegative);

  final Duration duration;

  Stream<Duration> get stream => _countdownStream();

  Stream<Duration> _countdownStream() async* {
    int remaining = duration.inSeconds;
    while (remaining > 0) {
      yield Duration(seconds: remaining);
      await Future<void>.delayed(const Duration(seconds: 1));
      remaining--;
    }
    yield Duration.zero;
  }
}