import 'dart:async';

/// 倒计时
class CountdownTimer {
  /// 倒计时时间
  final Duration initialDuration;

  /// 是否自动开始
  final bool autoRestart;

  /// 剩余时间
  late Duration _remainingTime;

  /// 最后更新时间
  DateTime? _lastUpdate;

  /// 定时器
  Timer? _timer;

  /// 是否已完成
  bool _isCompleted = false;

  /// 倒计时更新回调
  Function(Duration)? onTick;

  /// 倒计时结束回调
  Function()? onCompleted;

  CountdownTimer({
    this.initialDuration = const Duration(minutes: 30),
    this.autoRestart = true,
  }) {
    _remainingTime = initialDuration;
  }

  Duration get currentDuration => _remainingTime;

  /// 开始
  void start() {
    _lastUpdate = DateTime.now();
    _timer?.cancel();
    _timer = Timer.periodic(const Duration(milliseconds: 16), _handleTick);
  }

  /// 暂停
  void pause() {
    _timer?.cancel();
    _lastUpdate = null;
  }

  /// 重置
  void reset() {
    _timer?.cancel();
    _remainingTime = initialDuration;
    _isCompleted = false;
    _lastUpdate = null;
    onTick?.call(_remainingTime);
  }

  /// 结束倒计时
  void dispose() {
    _timer?.cancel();
    _timer = null;
  }

  /// 处理更新
  void _handleTick(Timer timer) {
    if (_lastUpdate == null) return;

    final now = DateTime.now();
    final elapsed = now.difference(_lastUpdate!);

    if (!_isCompleted) {
      _remainingTime -= elapsed;
      if (_remainingTime <= Duration.zero) {
        _remainingTime = Duration.zero;
        _isCompleted = true;
        onCompleted?.call();
      }
    } else if (autoRestart) {
      _remainingTime = initialDuration - elapsed;
      _isCompleted = false;
    }

    _lastUpdate = now;
    onTick?.call(_remainingTime);
  }

  /// 格式化时间，格式：分:秒:毫秒
  static String format(Duration duration) {
    String twoDigits(int n) => n.toString().padLeft(2, '0');
    String threeDigits(int n) => n.toString().padLeft(2, '0').substring(0, 2);

    return "${twoDigits(duration.inMinutes)}:"
        "${twoDigits(duration.inSeconds % 60)}:"
        "${threeDigits(duration.inMilliseconds % 1000)}";
  }
}