using System;
using System.IO;
using System.Net;
using System.Net.Security;
using System.Net.Sockets;
using System.Security.Authentication;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;
using System.Threading;
using System.Threading.Tasks;
using MessagePack;
using Serilog;
using Serilog.Core;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Ipc;

namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Tests.Ipc;

/// <summary>
///     Round-trip tests for <see cref="TcpFrameServer"/> added with the TCP transport. Each
///     scenario binds the server on <c>127.0.0.1:0</c>, connects a real <see cref="TcpClient"/>,
///     performs the Hello handshake, and exercises a request/reply over the wire framing — both
///     plaintext and over TLS. These target net48 and run on Windows in CI; on the macOS dev box
///     they only compile.
/// </summary>
public sealed class TcpRoundTripTests
{
    private static readonly ILogger Quiet = Logger.None;

    // Generous timeout so the deterministic tests don't hang CI if the server misbehaves.
    private static readonly TimeSpan Timeout = TimeSpan.FromSeconds(10);

    /// <summary>
    ///     Fake handler that echoes a fixed <see cref="ReadRawReply"/> when it sees a
    ///     <see cref="MessageKind.ReadRawRequest"/>, mirroring the client correlation id.
    /// </summary>
    private sealed class EchoHandler : IFrameHandler
    {
        public Task HandleAsync(MessageKind kind, byte[] body, FrameWriter writer, CancellationToken ct)
        {
            if (kind != MessageKind.ReadRawRequest)
                return Task.CompletedTask;

            var request = MessagePackSerializer.Deserialize<ReadRawRequest>(body);
            var reply = new ReadRawReply
            {
                CorrelationId = request.CorrelationId,
                Success = true,
                Samples = new[]
                {
                    new HistorianSampleDto
                    {
                        ValueBytes = MessagePackSerializer.Serialize(42.0),
                        Quality = 192,
                        TimestampUtcTicks = new DateTime(2026, 6, 12, 0, 0, 0, DateTimeKind.Utc).Ticks,
                    },
                },
            };
            return writer.WriteAsync(MessageKind.ReadRawReply, reply, ct);
        }
    }

    /// <summary>Generates an in-memory self-signed RSA cert with a serverAuth EKU and a private key.</summary>
    private static X509Certificate2 MakeSelfSignedCert()
    {
        using var rsa = RSA.Create(2048);
        var req = new CertificateRequest("CN=otopcua-historian-sidecar-test", rsa, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);
        req.CertificateExtensions.Add(
            new X509EnhancedKeyUsageExtension(
                new OidCollection { new Oid("1.3.6.1.5.5.7.3.1") /* serverAuth */ }, critical: false));
        using var ephemeral = req.CreateSelfSigned(DateTimeOffset.UtcNow.AddDays(-1), DateTimeOffset.UtcNow.AddYears(1));
        // Round-trip through a PFX so the returned cert carries an exportable private key on net48.
        var pfx = ephemeral.Export(X509ContentType.Pfx, "pw");
        return new X509Certificate2(pfx, "pw", X509KeyStorageFlags.Exportable);
    }

    /// <summary>Performs the Hello handshake on the given stream and returns the deserialized ack.</summary>
    private static async Task<HelloAck> HelloAsync(Stream stream, string secret, CancellationToken ct)
    {
        using var writer = new FrameWriter(stream, leaveOpen: true);
        using var reader = new FrameReader(stream, leaveOpen: true);

        await writer.WriteAsync(MessageKind.Hello,
            new Hello { ProtocolMajor = Hello.CurrentMajor, PeerName = "test-client", SharedSecret = secret }, ct);

        var ackFrame = await reader.ReadFrameAsync(ct);
        ackFrame.ShouldNotBeNull();
        ackFrame!.Value.Kind.ShouldBe(MessageKind.HelloAck);
        return MessagePackSerializer.Deserialize<HelloAck>(ackFrame.Value.Body);
    }

    /// <summary>Wraps a connected client socket stream in an SslStream that pins the server cert thumbprint.</summary>
    private static async Task<SslStream> ClientTlsAsync(NetworkStream inner, string expectedThumbprint, CancellationToken ct)
    {
        var ssl = new SslStream(inner, leaveInnerStreamOpen: false,
            userCertificateValidationCallback: (_, cert, _, _) =>
                cert is not null &&
                string.Equals(
                    cert.GetCertHashString(),
                    expectedThumbprint,
                    StringComparison.OrdinalIgnoreCase));
        await ssl.AuthenticateAsClientAsync("otopcua-historian-sidecar-test", clientCertificates: null,
            enabledSslProtocols: SslProtocols.Tls12, checkCertificateRevocation: false);
        return ssl;
    }

    /// <summary>Plaintext: Hello (good secret) is accepted and a ReadRaw request is echoed back.</summary>
    [Fact]
    public async Task Plaintext_RoundTrip_HelloAcceptedAndRequestEchoed()
    {
        using var cts = new CancellationTokenSource(Timeout);
        using var server = new TcpFrameServer(IPAddress.Loopback, 0, "shh", tlsCert: null, Quiet);
        var serverTask = server.RunOneConnectionAsync(new EchoHandler(), cts.Token);

        using var client = new TcpClient();
        await client.ConnectAsync(IPAddress.Loopback, server.BoundPort);
        var stream = client.GetStream();

        var ack = await HelloAsync(stream, "shh", cts.Token);
        ack.Accepted.ShouldBeTrue();

        using var writer = new FrameWriter(stream, leaveOpen: true);
        using var reader = new FrameReader(stream, leaveOpen: true);

        await writer.WriteAsync(MessageKind.ReadRawRequest,
            new ReadRawRequest { TagName = "Tank.Level", MaxValues = 10, CorrelationId = "corr-1" }, cts.Token);

        var replyFrame = await reader.ReadFrameAsync(cts.Token);
        replyFrame.ShouldNotBeNull();
        replyFrame!.Value.Kind.ShouldBe(MessageKind.ReadRawReply);
        var reply = MessagePackSerializer.Deserialize<ReadRawReply>(replyFrame.Value.Body);
        reply.Success.ShouldBeTrue();
        reply.CorrelationId.ShouldBe("corr-1");
        reply.Samples.Length.ShouldBe(1);
        MessagePackSerializer.Deserialize<double>(reply.Samples[0].ValueBytes!).ShouldBe(42.0);

        client.Close();
        await serverTask;
    }

    /// <summary>TLS: a self-signed server cert; the client pins its thumbprint; same exchange succeeds.</summary>
    [Fact]
    public async Task Tls_RoundTrip_HelloAcceptedAndRequestEchoed()
    {
        using var cts = new CancellationTokenSource(Timeout);
        using var cert = MakeSelfSignedCert();
        using var server = new TcpFrameServer(IPAddress.Loopback, 0, "shh", tlsCert: cert, Quiet);
        var serverTask = server.RunOneConnectionAsync(new EchoHandler(), cts.Token);

        using var client = new TcpClient();
        await client.ConnectAsync(IPAddress.Loopback, server.BoundPort);
        using var ssl = await ClientTlsAsync(client.GetStream(), cert.Thumbprint, cts.Token);

        var ack = await HelloAsync(ssl, "shh", cts.Token);
        ack.Accepted.ShouldBeTrue();

        using var writer = new FrameWriter(ssl, leaveOpen: true);
        using var reader = new FrameReader(ssl, leaveOpen: true);

        await writer.WriteAsync(MessageKind.ReadRawRequest,
            new ReadRawRequest { TagName = "Tank.Level", MaxValues = 10, CorrelationId = "tls-1" }, cts.Token);

        var replyFrame = await reader.ReadFrameAsync(cts.Token);
        replyFrame.ShouldNotBeNull();
        replyFrame!.Value.Kind.ShouldBe(MessageKind.ReadRawReply);
        var reply = MessagePackSerializer.Deserialize<ReadRawReply>(replyFrame.Value.Body);
        reply.Success.ShouldBeTrue();
        reply.CorrelationId.ShouldBe("tls-1");

        client.Close();
        await serverTask;
    }

    /// <summary>
    ///     TLS: when the client pins a wrong thumbprint the validation callback returns false,
    ///     causing <see cref="SslStream.AuthenticateAsClientAsync"/> to throw
    ///     <see cref="AuthenticationException"/> before any Hello is exchanged.
    /// </summary>
    [Fact]
    public async Task Tls_BadThumbprint_AuthenticationFails()
    {
        using var cts = new CancellationTokenSource(Timeout);
        using var cert = MakeSelfSignedCert();
        using var server = new TcpFrameServer(IPAddress.Loopback, 0, "shh", tlsCert: cert, Quiet);
        var serverTask = server.RunOneConnectionAsync(new EchoHandler(), cts.Token);

        using var client = new TcpClient();
        await client.ConnectAsync(IPAddress.Loopback, server.BoundPort);

        // Deliberately pin the wrong thumbprint — all zeros.
        const string wrongThumbprint = "0000000000000000000000000000000000000000";
        var ssl = new SslStream(client.GetStream(), leaveInnerStreamOpen: false,
            userCertificateValidationCallback: (_, serverCert, _, _) =>
                serverCert is not null &&
                string.Equals(serverCert.GetCertHashString(), wrongThumbprint, StringComparison.OrdinalIgnoreCase));

        await Should.ThrowAsync<AuthenticationException>(async () =>
            await ssl.AuthenticateAsClientAsync("otopcua-historian-sidecar-test", clientCertificates: null,
                enabledSslProtocols: SslProtocols.Tls12, checkCertificateRevocation: false));

        ssl.Dispose();
        // Server will see the broken TLS handshake and end the connection; let it finish.
        try { await serverTask; } catch { /* server may throw on the aborted TLS */ }
    }

    /// <summary>Bad secret: Hello is rejected with Accepted=false and the shared-secret-mismatch reason.</summary>
    [Fact]
    public async Task BadSecret_HelloRejected()
    {
        using var cts = new CancellationTokenSource(Timeout);
        using var server = new TcpFrameServer(IPAddress.Loopback, 0, "right-secret", tlsCert: null, Quiet);
        var serverTask = server.RunOneConnectionAsync(new EchoHandler(), cts.Token);

        using var client = new TcpClient();
        await client.ConnectAsync(IPAddress.Loopback, server.BoundPort);

        var ack = await HelloAsync(client.GetStream(), "wrong-secret", cts.Token);
        ack.Accepted.ShouldBeFalse();
        ack.RejectReason.ShouldBe("shared-secret-mismatch");

        client.Close();
        await serverTask;
    }

    /// <summary>
    ///     Single-active serial accept: while client A is connected (Hello done), client B's
    ///     Hello does not complete until A disconnects. The server only accepts one connection
    ///     per <see cref="TcpFrameServer.RunOneConnectionAsync"/>, so B's handshake is served by
    ///     the second loop iteration that runs only after A's connection ends.
    /// </summary>
    [Fact]
    public async Task SingleActive_SecondClientHelloCompletesOnlyAfterFirstCloses()
    {
        using var cts = new CancellationTokenSource(Timeout);
        using var server = new TcpFrameServer(IPAddress.Loopback, 0, "shh", tlsCert: null, Quiet);

        // Run the server loop: it accepts one connection at a time, serially.
        var serverLoop = server.RunAsync(new EchoHandler(), cts.Token);

        // Client A connects and completes its Hello — it now owns the single active slot.
        using var clientA = new TcpClient();
        await clientA.ConnectAsync(IPAddress.Loopback, server.BoundPort);
        var ackA = await HelloAsync(clientA.GetStream(), "shh", cts.Token);
        ackA.Accepted.ShouldBeTrue();

        // Client B connects. The TCP connect may complete (OS backlog) but the server is still
        // busy with A, so B's Hello round-trip must NOT complete yet.
        using var clientB = new TcpClient();
        await clientB.ConnectAsync(IPAddress.Loopback, server.BoundPort);
        var bHelloTask = HelloAsync(clientB.GetStream(), "shh", cts.Token);

        // Give B a chance to (wrongly) complete — it must remain pending while A is connected.
        var earlyWinner = await Task.WhenAny(bHelloTask, Task.Delay(TimeSpan.FromMilliseconds(500), cts.Token));
        earlyWinner.ShouldNotBe(bHelloTask, "client B's Hello completed while client A was still connected");

        // Now disconnect A. The server's next loop iteration accepts B and serves its Hello.
        clientA.Close();

        var ackB = await bHelloTask;
        ackB.Accepted.ShouldBeTrue();

        // Tear down: cancel the loop and let it unwind.
        cts.Cancel();
        try { await serverLoop; } catch (OperationCanceledException) { /* expected */ }
    }

    [Fact]
    public async Task BindFailure_SurfacesBindError_NotPermanentNotListening()
    {
        // Regression (live-caught 2026-06-12): when TcpFrameServer's listener bind fails (port in a
        // Windows excluded range → WSAEACCES, or already in use), the failure must surface as the
        // bind SocketException on EVERY accept attempt — NOT a one-time bind error followed by a
        // permanent InvalidOperationException "Not listening". The latter is the assign-before-Start
        // wedge: a non-null-but-unstarted listener that EnsureListening's guard never re-Starts,
        // which crash-looped the live sidecar on the reserved port 32569.
        using var cts = new CancellationTokenSource(Timeout);

        // Occupy a loopback port exclusively so the server's Start() bind is forbidden.
        var blocker = new TcpListener(IPAddress.Loopback, 0) { ExclusiveAddressUse = true };
        blocker.Start();
        try
        {
            var takenPort = ((IPEndPoint)blocker.LocalEndpoint).Port;
            using var server = new TcpFrameServer(IPAddress.Loopback, takenPort, "shh", tlsCert: null, Quiet);

            // First accept attempt: the bind fails with a SocketException.
            await Should.ThrowAsync<SocketException>(() => server.RunOneConnectionAsync(new EchoHandler(), cts.Token));

            // Second attempt MUST also be the bind SocketException — not InvalidOperationException
            // "Not listening". This is the assertion that fails against the assign-before-Start bug.
            var second = await Should.ThrowAsync<Exception>(() => server.RunOneConnectionAsync(new EchoHandler(), cts.Token));
            second.ShouldBeOfType<SocketException>();
        }
        finally { blocker.Stop(); }
    }
}