using Fleet.Core;
using Fleet.Link;
using MoShiro.Measurement;
using MoShiro.Protocol;

namespace MoShiro.Agent;

/// <summary>
/// 一条线路（本节点拨号到一个监听节点的一个 IP 族）的状态：控制层和 QUIC 数据通道各一个状态机，状态迁移只在这里发生、只在这里记日志。
/// 控制层每次迁移写一条 <c>link state</c>；数据通道只在“可用 ↔ 不可用”的边界上写，重拨过程中的失败只计数。
/// </summary>
public sealed class LinkStatus
{
    private const int MaxHandshakeSamples = 128;

    private readonly object _gate = new();
    private readonly string _listenerId;
    private readonly string _ipVersion;
    private readonly TimeProvider _time;
    private readonly Queue<double> _handshakeMs = new();

    private ControlState _control = ControlState.Dialing;
    private long _controlSince;
    private LinkFault? _controlFault;
    private int _controlAttempt;
    private long? _controlRetryAt;

    private QuicState _quic = QuicState.Idle;
    private long _quicSince;
    private long? _quicDownSince;
    private LinkFault? _quicFault;
    private int _quicAttempt;
    private long? _quicRetryAt;

    private long _handshakeAttempts;
    private long _handshakeSuccesses;
    private long _handshakeFailures;
    private long _handshakeTimeouts;

    public LinkStatus(string listenerId, string ipVersion, TimeProvider time, INodeLog log)
    {
        _listenerId = listenerId;
        _ipVersion = ipVersion;
        _time = time;
        Log = log;
        _controlSince = _quicSince = Now();
    }

    /// <summary>当前这次尝试的日志（带 attempt_id 等上下文）；控制层每次重拨前由连接更新。</summary>
    public INodeLog Log { get; set; }

    public ControlState Control
    {
        get
        {
            lock (_gate)
            {
                return _control;
            }
        }
    }

    public QuicState Quic
    {
        get
        {
            lock (_gate)
            {
                return _quic;
            }
        }
    }

    public bool Ready => Control == ControlState.Up && Quic == QuicState.Ready;

    public void SetControl(ControlState state, LinkFault? fault = null, int attempt = 0, TimeSpan? retryIn = null)
    {
        ControlState from;
        long inStateMs;
        lock (_gate)
        {
            from = _control;
            long now = Now();
            inStateMs = now - _controlSince;
            if (state != from)
            {
                _controlSince = now;
            }

            _control = state;
            _controlFault = state == ControlState.Up ? null : fault ?? _controlFault;
            _controlAttempt = attempt;
            _controlRetryAt = retryIn is { } delay ? now + (long)delay.TotalMilliseconds : null;
        }

        if (state == from)
        {
            return;
        }

        string reason = state == ControlState.Backoff && fault is not null ? fault.ToString() : "";
        Log.Write(state == ControlState.Backoff ? NodeLogLevel.Warn : NodeLogLevel.Info, "link state",
        [
            ("layer", "control"), ("listener", _listenerId), ("ip_version", _ipVersion), ("from", Name(from)), ("to", Name(state)),
            ("in_state_ms", inStateMs), ("attempt", attempt), ("retry_in_ms", retryIn is { } r ? (long)r.TotalMilliseconds : null),
            ("reason", reason.Length == 0 ? null : reason),
        ]);
    }

    public void SetQuic(QuicState state, LinkFault? fault = null, int attempt = 0, TimeSpan? retryIn = null)
    {
        QuicState from;
        long? downMs = null;
        bool logged;
        lock (_gate)
        {
            from = _quic;
            long now = Now();
            if (state != from)
            {
                _quicSince = now;
            }

            if (state == QuicState.Ready)
            {
                downMs = _quicDownSince is { } down ? now - down : null;
                _quicDownSince = null;
                _quicFault = null;
            }
            else if (state is QuicState.Retrying or QuicState.Connecting)
            {
                _quicDownSince ??= now;
                _quicFault = fault ?? _quicFault;
            }
            else
            {
                _quicDownSince = null;
            }

            // 数据通道抖动时不逐次打印：恢复可用、首次失败时各一条，重拨中的失败只计数。
            logged = state == QuicState.Ready || (state == QuicState.Retrying && (from == QuicState.Ready || attempt == 1));
            _quic = state;
            _quicAttempt = attempt;
            _quicRetryAt = retryIn is { } delay ? now + (long)delay.TotalMilliseconds : null;
        }

        if (logged)
        {
            Log.Write(state == QuicState.Retrying ? NodeLogLevel.Warn : NodeLogLevel.Info, "link state",
            [
                ("layer", "task_quic"), ("listener", _listenerId), ("ip_version", _ipVersion), ("from", Name(from)), ("to", Name(state)),
                ("down_ms", downMs), ("attempt", attempt), ("retry_in_ms", retryIn is { } r ? (long)r.TotalMilliseconds : null),
                ("reason", state == QuicState.Retrying ? fault?.ToString() : null),
            ]);
        }
    }

    /// <summary>记录一次 QUIC 握手的结果。</summary>
    public void Handshake(bool succeeded, double? elapsedMs, bool timedOut)
    {
        lock (_gate)
        {
            _handshakeAttempts++;
            if (succeeded)
            {
                _handshakeSuccesses++;
                if (elapsedMs is { } ms)
                {
                    _handshakeMs.Enqueue(ms);
                    while (_handshakeMs.Count > MaxHandshakeSamples)
                    {
                        _handshakeMs.Dequeue();
                    }
                }
            }
            else
            {
                _handshakeFailures++;
                if (timedOut)
                {
                    _handshakeTimeouts++;
                }
            }
        }
    }

    public LinkHealth Snapshot(Outbox outbox, int tcpBlocks, QuicTransportSnapshot? transport)
    {
        lock (_gate)
        {
            long now = Now();
            double? p95 = null;
            if (_handshakeMs.Count > 0)
            {
                double[] sorted = [.. _handshakeMs.Order()];
                p95 = sorted[(int)Math.Ceiling(sorted.Length * 0.95) - 1];
            }

            return new LinkHealth
            {
                ListenerId = _listenerId,
                IpVersion = _ipVersion,
                Control = new ControlHealth
                {
                    State = _control,
                    SinceMs = _controlSince,
                    LastError = _controlFault,
                    RetryAttempt = _controlAttempt,
                    RetryInMs = _control == ControlState.Backoff ? RetryIn(_controlRetryAt, now) : null,
                    OutboxBytes = outbox.PendingBytes,
                    OutboxPending = outbox.PendingCount,
                },
                Task = new TaskHealth
                {
                    TcpBlocks = tcpBlocks,
                    Quic = new QuicHealth
                    {
                        State = _quic,
                        SinceMs = _quicSince,
                        LastError = _quicFault,
                        RetryAttempt = _quicAttempt,
                        RetryInMs = _quic == QuicState.Retrying ? RetryIn(_quicRetryAt, now) : null,
                        HandshakeAttempts = _handshakeAttempts,
                        HandshakeSuccesses = _handshakeSuccesses,
                        HandshakeFailures = _handshakeFailures,
                        HandshakeTimeouts = _handshakeTimeouts,
                        HandshakeP95Ms = p95,
                        HandshakeSampleCount = _handshakeMs.Count,
                        TransportPacketLossRate = transport?.PacketLossRate,
                        TransportPacketsSent = transport?.PacketsSent,
                        TransportCongestionEvents = transport?.CongestionEvents,
                        TransportEcnCongestionEvents = transport?.EcnCongestionEvents,
                        PathMtu = transport?.PathMtu,
                    },
                },
            };
        }
    }

    private static long? RetryIn(long? at, long now) => at is { } t ? Math.Max(0, t - now) : null;

    private long Now() => _time.GetUtcNow().ToUnixTimeMilliseconds();

    private static string Name(ControlState state) => state.ToString().ToLowerInvariant();

    private static string Name(QuicState state) => state.ToString().ToLowerInvariant();
}