using System.IO;
using System.IO.Pipes;
using MessagePack;
using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared;
using ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Shared.Contracts;

namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Ipc;

/// <summary>
///     Proxy-side IPC channel to a running <c>Driver.FOCAS.Host</c>. Owns the pipe connection
///     and serializes request/response round-trips through a single call gate so
///     concurrent callers don't interleave frames. One instance per FOCAS Host session.
/// </summary>
public sealed class FocasIpcClient : IAsyncDisposable
{
    private readonly Stream _stream;
    private readonly FrameReader _reader;
    private readonly FrameWriter _writer;
    private readonly SemaphoreSlim _callGate = new(1, 1);

    private FocasIpcClient(Stream stream)
    {
        _stream = stream;
        _reader = new FrameReader(stream, leaveOpen: true);
        _writer = new FrameWriter(stream, leaveOpen: true);
    }

    /// <summary>Named-pipe factory: connects, sends Hello, awaits HelloAck.</summary>
    public static async Task<FocasIpcClient> ConnectAsync(
        string pipeName, string sharedSecret, TimeSpan connectTimeout, CancellationToken ct)
    {
        var stream = new NamedPipeClientStream(
            serverName: ".",
            pipeName: pipeName,
            direction: PipeDirection.InOut,
            options: PipeOptions.Asynchronous);

        await stream.ConnectAsync((int)connectTimeout.TotalMilliseconds, ct);
        return await HandshakeAsync(stream, sharedSecret, ct).ConfigureAwait(false);
    }

    /// <summary>
    ///     Stream factory — used by tests that wire the Proxy against an in-memory stream
    ///     pair instead of a real pipe. <paramref name="stream"/> is owned by the caller
    ///     until <see cref="DisposeAsync"/>.
    /// </summary>
    public static Task<FocasIpcClient> ConnectAsync(Stream stream, string sharedSecret, CancellationToken ct)
        => HandshakeAsync(stream, sharedSecret, ct);

    private static async Task<FocasIpcClient> HandshakeAsync(Stream stream, string sharedSecret, CancellationToken ct)
    {
        var client = new FocasIpcClient(stream);
        try
        {
            await client._writer.WriteAsync(FocasMessageKind.Hello,
                new Hello { PeerName = "FOCAS.Proxy", SharedSecret = sharedSecret }, ct).ConfigureAwait(false);

            var ack = await client._reader.ReadFrameAsync(ct).ConfigureAwait(false);
            if (ack is null || ack.Value.Kind != FocasMessageKind.HelloAck)
                throw new InvalidOperationException("Did not receive HelloAck from FOCAS.Host");

            var ackMsg = FrameReader.Deserialize<HelloAck>(ack.Value.Body);
            if (!ackMsg.Accepted)
                throw new UnauthorizedAccessException($"FOCAS.Host rejected Hello: {ackMsg.RejectReason}");

            return client;
        }
        catch
        {
            await client.DisposeAsync().ConfigureAwait(false);
            throw;
        }
    }

    public async Task<TResp> CallAsync<TReq, TResp>(
        FocasMessageKind requestKind, TReq request, FocasMessageKind expectedResponseKind, CancellationToken ct)
    {
        await _callGate.WaitAsync(ct).ConfigureAwait(false);
        try
        {
            await _writer.WriteAsync(requestKind, request, ct).ConfigureAwait(false);

            var frame = await _reader.ReadFrameAsync(ct).ConfigureAwait(false);
            if (frame is null) throw new EndOfStreamException("FOCAS IPC peer closed before response");

            if (frame.Value.Kind == FocasMessageKind.ErrorResponse)
            {
                var err = MessagePackSerializer.Deserialize<ErrorResponse>(frame.Value.Body);
                throw new FocasIpcException(err.Code, err.Message);
            }

            if (frame.Value.Kind != expectedResponseKind)
                throw new InvalidOperationException(
                    $"Expected {expectedResponseKind}, got {frame.Value.Kind}");

            return MessagePackSerializer.Deserialize<TResp>(frame.Value.Body);
        }
        finally { _callGate.Release(); }
    }

    public async Task SendOneWayAsync<TReq>(FocasMessageKind requestKind, TReq request, CancellationToken ct)
    {
        await _callGate.WaitAsync(ct).ConfigureAwait(false);
        try { await _writer.WriteAsync(requestKind, request, ct).ConfigureAwait(false); }
        finally { _callGate.Release(); }
    }

    public async ValueTask DisposeAsync()
    {
        _callGate.Dispose();
        _reader.Dispose();
        _writer.Dispose();
        await _stream.DisposeAsync().ConfigureAwait(false);
    }
}

public sealed class FocasIpcException(string code, string message) : Exception($"[{code}] {message}")
{
    public string Code { get; } = code;
}