using System.Net;
using System.Text.Json;
using Fleet.Core;
using MoShiro.Protocol;

namespace MoShiro.Measurement;

/// <summary>
/// 数据面会话：<c>session_id</c> 和密钥（由点对点握手里的 ECDH 派生）。两端的数据面包都用它认证。
/// Agent 的会话还带重放窗口等状态，所以是可以继承的。
/// </summary>
public class DataSession
{
    private IDatagramConnection? _datagramConnection;

    public DataSession(long sessionId, byte[] key)
    {
        SessionId = sessionId;
        Key = key;
    }

    public long SessionId { get; }

    public byte[] Key { get; }

    /// <summary>Public node identity for diagnostics; never the data-session identifier or key.</summary>
    public virtual string? DiagnosticPeerId => null;

    public IDatagramConnection? DatagramConnection => Volatile.Read(ref _datagramConnection);

    public void BindDatagramConnection(IDatagramConnection connection) => Volatile.Write(ref _datagramConnection, connection);

    /// <summary>对端最近一次通过认证的 UDP 源地址（监听方把单向数据发往这里；拨号方不需要）。</summary>
    public virtual IPEndPoint? DatagramRemoteEndPoint => null;

    /// <summary>TCP 首帧的随机数只能用一次。拨号方不接受连接，所以默认放行。</summary>
    public virtual bool UseNonce(ReadOnlySpan<byte> nonce) => true;
}

/// <summary>Unreliable QUIC datagram sender bound to one authenticated measurement session.</summary>
public interface IDatagramConnection
{
    bool Send(ReadOnlySpan<byte> datagram);
}

/// <summary>Transport-layer QUIC counters. These are separate from application Datagram delivery/loss.</summary>
public sealed record QuicTransportSnapshot(double? PacketLossRate, ulong PacketsSent, uint CongestionEvents, uint EcnCongestionEvents, ushort PathMtu);

public interface IDataSessions
{
    DataSession? Find(long sessionId);
}

/// <summary>只有一个会话（拨号方：与某个监听方的会话）。</summary>
public sealed class SingleSession : IDataSessions
{
    private readonly DataSession _session;

    public SingleSession(DataSession session)
    {
        _session = session;
    }

    public DataSession? Find(long sessionId) => sessionId == _session.SessionId ? _session : null;
}

public enum Admission
{
    Accepted,
    Invalid,
    RateLimited,
}

/// <summary>
/// 监听方的准入策略（安全边界）：重放窗口、令牌桶限速、源地址学习。积木本身不含任何策略；
/// 拨号方不需要，只做 MAC 校验。任何一步失败都是静默丢弃并计数，不回复。
/// </summary>
public interface IAdmission
{
    /// <summary>UDP 包：<paramref name="source"/> 是认证通过的源地址（实现可以据此学习 NAT 重绑定）。</summary>
    Admission AdmitDatagram(DataSession session, in MeasurementDatagramHeader header, SocketAddress source, long nowUs);

    /// <summary>TCP 回显的一条消息（只限速）。</summary>
    bool AdmitMessage(DataSession session, uint streamId, long nowUs);
}

/// <summary>数据面计数（只有计数，没有主机信息）：用于心跳和面板上的节点状态。</summary>
public sealed class DataPlaneCounters
{
    private long _packetsIn;
    private long _packetsOut;
    private long _invalid;
    private long _rateLimited;

    public long PacketsIn => Interlocked.Read(ref _packetsIn);

    public long PacketsOut => Interlocked.Read(ref _packetsOut);

    public long DroppedInvalid => Interlocked.Read(ref _invalid);

    public long DroppedRateLimited => Interlocked.Read(ref _rateLimited);

    public void PacketIn() => Interlocked.Increment(ref _packetsIn);

    public void PacketOut() => Interlocked.Increment(ref _packetsOut);

    public void DropInvalid() => Interlocked.Increment(ref _invalid);

    public void DropRateLimited() => Interlocked.Increment(ref _rateLimited);
}

/// <summary>一个列块属于线路任务还是按需测试的某个阶段。</summary>
public sealed record FragmentScope(TaskId? Task, TestId? Test, int? Phase);

/// <summary>
/// 积木交出一侧的行的地方。拨号方：放进发给 Agent 的发件箱（列块）；Agent 自己运行的积木（目标任务）：直接盖章上传。
/// </summary>
public interface IFragmentSink
{
    void Ship(string kind, FragmentScope scope, IReadOnlyList<RawStream> streams, IReadOnlyDictionary<string, JsonElement>? parameters, long startUtcMs, int durationMs, int port);
}

public enum FlushMode
{
    /// <summary>只交出已经稳定的行（回显类等过宽限期的）。</summary>
    Settled,

    /// <summary>交出全部（阶段结束或角色停止）。</summary>
    All,
}

/// <summary>积木无法继续（例如监听方等不到对端的地址）：由编排者决定整个测试怎么结束。</summary>
public sealed class BlockFaultException : Exception
{
    public BlockFaultException(string message)
        : base(message)
    {
    }
}

/// <summary>
/// 一个运行中的积木角色。同一种采集方法的两端是一对角色（拨号方和监听方），写在同一个文件里，
/// 共用包的构造、校验、行的记录；它们只产生<b>原始列</b>，不做任何统计，也不知道上层的方案或协议。
/// </summary>
public interface IBlock
{
    /// <summary>运行到取消（回显、保持）或到自己结束（单向数据流的发送端）。</summary>
    Task RunAsync(CancellationToken ct);

    /// <summary>
    /// 拨号方把已完成的行切成列块交给 <see cref="IFragmentSink"/>，返回块数；监听方返回 0（它的行留在 <see cref="Records"/> 里等合并）。
    /// <paramref name="peerProduced"/>：对端是行的主导方时，对端产生的行数（单向数据流的发送包数）。
    /// </summary>
    int Flush(FlushMode mode, long peerProduced = 0);

    /// <summary>这一侧作为主导方产生的行数（发出的包数）。</summary>
    long Produced { get; }

    /// <summary>这一侧为合并保留的按键记录；没有则为 null。</summary>
    RowStore? Records(string streamName);
}

/// <summary>运行一个积木所需的全部参数：Kind、已经校验并补全默认值的参数、流编号、端口、列块归属。</summary>
public sealed class BlockSpec
{
    public BlockSpec(KindSpec kind, ParamValues parameters, uint streamId, int port, FragmentScope scope)
    {
        Kind = kind;
        Params = parameters;
        StreamId = streamId;
        Port = port;
        Scope = scope;
    }

    public KindSpec Kind { get; }

    public ParamValues Params { get; }

    public uint StreamId { get; }

    public int Port { get; }

    public FragmentScope Scope { get; }

    public string KindId => Kind.Id;

    public long Int(string name) => Params.GetInt(name);

    public double Number(string name) => Params.GetNumber(name);

    public bool Bool(string name) => Params.GetBool(name);

    public string Text(string name) => Params.GetString(name);

    /// <summary>参数或端口变化时调和器重启这个积木（不含流编号：Agent 的流编号每次重建都会重新分配）。</summary>
    public string ConfigSignature => KindId + "|" + Port + "|" +
        string.Join(',', Params.Values.OrderBy(p => p.Key, StringComparer.Ordinal).Select(p => p.Key + "=" + p.Value.GetRawText()));

    /// <summary>参数、端口或流编号变化时重启：拨号方 据此判断 Agent 下发的任务有没有变（Agent 重启后流编号会变）。</summary>
    public string Signature => StreamId + "|" + ConfigSignature;

    /// <summary>校验参数（补全默认值）后构造；Kind 不存在或参数非法返回 null。</summary>
    public static BlockSpec? Create(string kindId, IReadOnlyDictionary<string, JsonElement> parameters, uint streamId, int port, FragmentScope scope)
    {
        KindSpec? kind = Kinds.Find(kindId);
        if (kind is null)
        {
            return null;
        }

        ParamResolution resolved = ParamResolver.Resolve(kind.Params, parameters);
        return resolved.IsValid ? new BlockSpec(kind, resolved.Values!, streamId, port, scope) : null;
    }
}

/// <summary>积木运行的环境：时钟、套接字、对端地址、列块出口。拨号方和监听方各自组装自己用得到的部分。</summary>
public sealed class BlockEnv
{
    public required MonoClock Clock { get; init; }

    public required INodeLog Log { get; init; }

    /// <summary>当前的数据面会话（拨号方固定；监听方是 Agent 当前的 拨号方 会话，可能没有）。</summary>
    public required Func<DataSession?> Session { get; init; }

    public QuicDatagramTransport? Datagrams { get; init; }

    /// <summary>拨号方：这条线路在每个时刻（单调时钟，微秒）丢包的历史概率（0 到 1），自适应探测用它在高发时段提前升频；没有历史为 null。</summary>
    public Func<long, double?>? LossPrior { get; init; }

    /// <summary>监听方的准入策略（限速等）；拨号方为 null。</summary>
    public IAdmission? Admission { get; init; }

    public DataPlaneCounters Counters { get; init; } = new();

    /// <summary>监听方：接受 TCP 数据连接。</summary>
    public TcpAcceptor? TcpListen { get; init; }

    /// <summary>拨号方：对端（Agent，或目标任务的目标地址）。</summary>
    public IPAddress? PeerAddress { get; init; }

    /// <summary>单个 Agent 任务的目标原文（http 是 URL，其余是主机[:端口]）；线路任务为 null。</summary>
    public string? Target { get; init; }

    /// <summary>单个 Agent 任务：解析出来的地址能不能连（本地 <c>allowed_target_cidrs</c>）；null 表示不限制。</summary>
    public Func<IPAddress, bool>? AllowAddress { get; init; }

    /// <summary>自适应频率的状态变化（用于审计）；null 表示不记录。</summary>
    public Action<RateChange>? OnRateChange { get; init; }

    /// <summary>拨号方：对端 TLS 证书的 SPKI 指纹；null 表示不校验证书（目标任务，目标是任意地址）。</summary>
    public byte[]? PeerSpkiSha256 { get; init; }

    /// <summary>拨号方：和对端（Agent）的配对敲门密钥；每条 TCP 连接建立后先发敲门包。null 表示对端不要求敲门（目标任务的任意地址）。</summary>
    public byte[]? KnockKey { get; init; }

    /// <summary>拨号方：列块出口。</summary>
    public IFragmentSink? Fragments { get; init; }

    /// <summary>本地硬上限：批量传输（tcp_transfer）发送端的码率（Mbit/s）。批量传输会尽可能占满链路，这是防止把小机器打满的保险。</summary>
    public double MaxBulkMbps { get; init; } = 100;

    /// <summary>本地硬上限：单向数据流接收缓冲的包速率上界。</summary>
    public long MaxPacketsPerSecond { get; init; } = 20_000;

    public TimeProvider Time => Clock.Time;

    /// <summary>同一套环境，但绑定到一个固定的数据面会话（Agent 为每个 拨号方 会话各起一组监听方积木）。</summary>
    public BlockEnv WithSession(DataSession session) =>
        new()
        {
            Clock = Clock,
            Log = Log,
            Session = () => session,
            Datagrams = Datagrams,
            LossPrior = LossPrior,
            Admission = Admission,
            Counters = Counters,
            TcpListen = TcpListen,
            PeerAddress = PeerAddress,
            Target = Target,
            AllowAddress = AllowAddress,
            OnRateChange = OnRateChange,
            PeerSpkiSha256 = PeerSpkiSha256,
            KnockKey = KnockKey,
            Fragments = Fragments,
            MaxBulkMbps = MaxBulkMbps,
            MaxPacketsPerSecond = MaxPacketsPerSecond,
        };
}