import 'dart:collection';

class PacketLossStatistics {
  static final PacketLossStatistics _instance =
      PacketLossStatistics._internal();
  factory PacketLossStatistics() => _instance;
  PacketLossStatistics._internal();

  // 记录每个messageId的分包信息
  // key: messageId, value: {totalPackets, receivedPackets}
  final Map<int, PacketInfo> _packetsMap = HashMap();

  // 配置参数
  int _maxCapacity = 300; // 最大容量为300条记录
  int _timeoutMs = 30000; // 默认超时时间为30秒

  // 统计信息
  int _totalMessages = 0; // 总消息数
  int _lostMessages = 0; // 丢包的消息数
  int _totalPackets = 0; // 总分包数
  int _lostPackets = 0; // 丢失的分包数

  // 记录分包数据
  void recordPacket(int messageId, int currentIndex, int totalPackets) {
    // 定期清理超时记录
    _cleanupExpiredPackets();

    // 检查容量限制
    _checkCapacityLimit();

    if (!_packetsMap.containsKey(messageId)) {
      _packetsMap[messageId] = PacketInfo(totalPackets);
      _totalMessages++;
      _totalPackets += totalPackets;
    } else {
      // 更新时间戳
      _packetsMap[messageId]!.timestamp = DateTime.now().millisecondsSinceEpoch;
    }

    _packetsMap[messageId]!.receivedPackets.add(currentIndex);

    // 如果收到了该messageId的最后一个包，进行统计
    if (currentIndex == totalPackets) {
      _checkPacketLoss(messageId);
    }
  }

  // 清理超时的记录
  void _cleanupExpiredPackets() {
    final currentTime = DateTime.now().millisecondsSinceEpoch;
    final expiredMessageIds = <int>[];

    _packetsMap.forEach((messageId, info) {
      // 如果记录超时，添加到待清理列表
      if (currentTime - info.timestamp > _timeoutMs) {
        expiredMessageIds.add(messageId);

        // 统计丢包
        _lostMessages++;
        _lostPackets += (info.totalPackets - info.receivedPackets.length);
      }
    });

    // 移除超时记录
    for (var messageId in expiredMessageIds) {
      _packetsMap.remove(messageId);
    }
  }

  // 检查并确保不超过最大容量
  void _checkCapacityLimit() {
    if (_packetsMap.length <= _maxCapacity) {
      return;
    }

    // 如果超过容量限制，按时间戳排序并删除最旧的记录
    var entries = _packetsMap.entries.toList()
      ..sort((a, b) => a.value.timestamp.compareTo(b.value.timestamp));

    // 计算需要移除的数量（移除25%的旧记录，至少保证有一定空间）
    int removeCount = (_packetsMap.length * 0.25).ceil();

    // 移除并统计丢包
    for (int i = 0; i < removeCount && i < entries.length; i++) {
      var entry = entries[i];
      _lostMessages++;
      _lostPackets +=
          (entry.value.totalPackets - entry.value.receivedPackets.length);
      _packetsMap.remove(entry.key);
    }
  }

  // 检查丢包情况
  void _checkPacketLoss(int messageId) {
    final info = _packetsMap[messageId]!;

    // 检查是否有丢失的包
    int received = info.receivedPackets.length;
    if (received < info.totalPackets) {
      _lostMessages++;
      _lostPackets += (info.totalPackets - received);
    }

    // 清理该messageId的记录，避免内存泄漏
    _packetsMap.remove(messageId);
  }

  // 获取丢包率统计信息
  PacketLossInfo getStatistics() {
    if (_totalMessages == 0 || _totalPackets == 0) {
      return PacketLossInfo(0.0, 0.0);
    }

    // 计算消息级别的丢包率
    double messageLossRate = (_lostMessages / _totalMessages) * 100;

    // 计算分包级别的丢包率
    double packetLossRate = (_lostPackets / _totalPackets) * 100;

    return PacketLossInfo(messageLossRate, packetLossRate);
  }

  // Getter和Setter，允许外部调整参数
  int get maxCapacity => _maxCapacity;
  set maxCapacity(int value) {
    if (value > 0) {
      _maxCapacity = value;
      // 设置新容量后立即检查
      _checkCapacityLimit();
    }
  }

  int get timeoutMs => _timeoutMs;
  set timeoutMs(int value) {
    if (value > 0) {
      _timeoutMs = value;
      // 设置新超时后立即清理
      _cleanupExpiredPackets();
    }
  }

  // 获取当前未完成记录数
  int get pendingRecordsCount => _packetsMap.length;

  // 重置统计数据
  void reset() {
    _packetsMap.clear();
    _totalMessages = 0;
    _lostMessages = 0;
    _totalPackets = 0;
    _lostPackets = 0;
  }
}

// 分包信息类
class PacketInfo {
  final int totalPackets;
  final Set<int> receivedPackets = HashSet<int>();
  int timestamp; // 添加时间戳字段，记录最后更新时间

  PacketInfo(this.totalPackets)
      : timestamp = DateTime.now().millisecondsSinceEpoch;
}

// 丢包统计信息类
class PacketLossInfo {
  final double messageLossRate; // 消息丢失率
  final double packetLossRate; // 分包丢失率

  PacketLossInfo(this.messageLossRate, this.packetLossRate);

  @override
  String toString() {
    return 'Message Loss Rate: ${messageLossRate.toStringAsFixed(2)}%, Packet Loss Rate: ${packetLossRate.toStringAsFixed(2)}%';
  }
}