using System.Collections.Concurrent;
using Fleet.Core;
using MoShiro.Protocol;

namespace MoShiro.Agent;

/// <summary>
/// 拨号侧的组装点：每个拨号目标（监听节点 × IP 族）一个 <see cref="DialConnection"/>。目标列表变化时只调和连接：
/// 新增的建立，移除的断开，地址或证书指纹变化的重建，其余不受影响。
/// </summary>
public sealed class DialerHost : IDisposable
{
    private readonly DialEnv _env;
    private readonly Dictionary<string, Running> _connections = [];
    private readonly ConcurrentDictionary<string, long> _pendingRetries = new(StringComparer.Ordinal);
    private readonly SemaphoreSlim _changed = new(0);
    private readonly TimeProvider _time;
    private readonly INodeLog _log;

    public DialerHost(DialEnv env, TimeProvider time, INodeLog log)
    {
        _env = env;
        _time = time;
        _log = log;
        env.Directory.Changed += () => _changed.Release();
    }

    public DialDirectory Directory => _env.Directory;

    /// <summary>某条路径的控制会话是否已经建立、QUIC 数据通道是否可发送（测试和状态查看用）。</summary>
    public bool IsConnected(string listenerId, string ipVersion = IpVersions.V4)
    {
        lock (_connections)
        {
            return _connections.TryGetValue(listenerId + "~" + ipVersion, out Running? running) && running.Connection.IsConnected;
        }
    }

    public DialConnection? Connection(string listenerId, string ipVersion = IpVersions.V4)
    {
        lock (_connections)
        {
            return _connections.TryGetValue(listenerId + "~" + ipVersion, out Running? running) ? running.Connection : null;
        }
    }

    /// <summary>每条路径当前的线路健康（随心跳上报）。</summary>
    public List<LinkHealth> SnapshotLinks()
    {
        DialConnection[] connections;
        lock (_connections)
        {
            connections = [.. _connections.Values.Select(r => r.Connection)];
        }

        return [.. connections.Select(c => c.Health())];
    }

    /// <summary>管理端手动重试：跳过这个监听节点所有路径的退避。目标列表还没到时，30 秒内到达就补上。</summary>
    public void RetryListener(string listenerId, bool queueIfMissing = true)
    {
        DialConnection[] matches;
        lock (_connections)
        {
            matches = [.. _connections.Values.Select(r => r.Connection).Where(c => c.Endpoint.NodeId == listenerId)];
        }

        if (matches.Length == 0)
        {
            if (queueIfMissing)
            {
                _pendingRetries[listenerId] = _time.GetUtcNow().AddSeconds(30).ToUnixTimeMilliseconds();
            }

            _log.Warn("manual link retry requested but no matching dial target is configured", ("listener", listenerId));
            return;
        }

        _pendingRetries.TryRemove(listenerId, out _);
        foreach (DialConnection connection in matches)
        {
            connection.RetryNow();
        }
    }

    public async Task RunAsync(CancellationToken ct)
    {
        try
        {
            while (!ct.IsCancellationRequested)
            {
                await ReconcileAsync(_env.Directory.Targets, ct);
                RetryPending();
                await _changed.WaitAsync(ct);
            }
        }
        catch (OperationCanceledException)
        {
            // 停止
        }
        finally
        {
            await ReconcileAsync([], CancellationToken.None);
        }
    }

    public void Dispose() => _changed.Dispose();

    private void RetryPending()
    {
        long now = _time.GetUtcNow().ToUnixTimeMilliseconds();
        foreach ((string listenerId, long expiresAt) in _pendingRetries.ToArray())
        {
            if (expiresAt <= now)
            {
                _pendingRetries.TryRemove(listenerId, out _);
            }
            else
            {
                RetryListener(listenerId, queueIfMissing: false);
            }
        }
    }

    private async Task ReconcileAsync(IReadOnlyList<DialEndpoint> targets, CancellationToken ct)
    {
        var wanted = targets.ToDictionary(t => t.PathKey);
        var stopped = new List<Running>();
        lock (_connections)
        {
            foreach ((string id, Running running) in _connections.ToList())
            {
                if (!wanted.TryGetValue(id, out DialEndpoint? endpoint) || !DialDirectory.Equal(endpoint, running.Connection.Endpoint))
                {
                    stopped.Add(running);
                    _connections.Remove(id);
                }
            }
        }

        foreach (Running running in stopped)
        {
            await running.StopAsync();
        }

        if (ct.IsCancellationRequested)
        {
            return;
        }

        lock (_connections)
        {
            foreach ((string id, DialEndpoint endpoint) in wanted)
            {
                if (!_connections.ContainsKey(id))
                {
                    _connections[id] = Running.Start(new DialConnection(endpoint, _env));
                }
            }
        }
    }

    private sealed class Running : IDisposable
    {
        private readonly CancellationTokenSource _cts = new();
        private Task _run = Task.CompletedTask;

        private Running(DialConnection connection)
        {
            Connection = connection;
        }

        public DialConnection Connection { get; }

        public static Running Start(DialConnection connection)
        {
            var running = new Running(connection);
            running._run = Task.Run(() => connection.RunAsync(running._cts.Token), CancellationToken.None);
            return running;
        }

        public async Task StopAsync()
        {
            await _cts.CancelAsync();
            try
            {
                await _run.WaitAsync(TimeSpan.FromSeconds(10));
            }
            catch (Exception ex) when (ex is OperationCanceledException or TimeoutException)
            {
                // 没有及时退出：不再等
            }

            Dispose();
        }

        public void Dispose()
        {
            Connection.Dispose();
            _cts.Dispose();
        }
    }
}