using System.Net;
using System.Net.Sockets;
using Mbproxy.Options;
using Mbproxy.Proxy;
using Mbproxy.Proxy.Supervision;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;
using Polly;
using Xunit;

namespace Mbproxy.Tests.Proxy.Supervision;

/// <summary>
/// End-to-end supervisor tests that run the proxy against the DL205 simulator.
/// These tests verify supervisor-level behaviour (recovery, counters) with a real
/// Modbus backend rather than a bare socket.
/// </summary>
[Collection(nameof(Mbproxy.Tests.Sim.DL205SimulatorCollection))]
[Trait("Category", "E2E")]
public sealed class SupervisorE2ETests
{
    private readonly Mbproxy.Tests.Sim.DL205SimulatorFixture _sim;

    public SupervisorE2ETests(Mbproxy.Tests.Sim.DL205SimulatorFixture sim)
    {
        _sim = sim;
    }

    // ── Helpers ───────────────────────────────────────────────────────────────────────────

    private static int PickFreePort()
    {
        var l = new TcpListener(IPAddress.Loopback, 0);
        l.Start();
        int port = ((IPEndPoint)l.LocalEndpoint).Port;
        l.Stop();
        return port;
    }

    private PlcListenerSupervisor BuildSimSupervisor(
        int listenPort,
        RecoveryProfile? recoveryProfile = null)
    {
        var profile = recoveryProfile ?? new RecoveryProfile
        {
            InitialBackoffMs = [200, 200],
            SteadyStateMs    = 200,
        };

        ILoggerFactory loggerFactory = NullLoggerFactory.Instance;

        var plcOpts = new PlcOptions
        {
            Name       = "SimPLC",
            ListenPort = listenPort,
            Host       = _sim.Host,
            Port       = _sim.Port,
        };
        var connOpts = new ConnectionOptions
        {
            BackendConnectTimeoutMs = 3000,
            BackendRequestTimeoutMs = 3000,
        };

        var recoveryPipeline = PolicyFactory.BuildListenerRecovery(profile, NullLogger.Instance);
        var backendPipeline  = PolicyFactory.BuildBackendConnect(
            new RetryProfile { MaxAttempts = 2, BackoffMs = [100, 500] },
            NullLogger.Instance);

        return new PlcListenerSupervisor(
            plc:                    plcOpts,
            connectionOptions:      connOpts,
            pipeline:               new NoopPduPipeline(),
            listenerLogger:         loggerFactory.CreateLogger<PlcListener>(),
            multiplexerLogger:      loggerFactory.CreateLogger<Mbproxy.Proxy.Multiplexing.PlcMultiplexer>(),
            pipeLogger:             loggerFactory.CreateLogger("Mbproxy.Proxy.UpstreamPipe.Test"),
            perPlcContext:          null,
            recoveryPipeline:       recoveryPipeline,
            logger:                 loggerFactory.CreateLogger<PlcListenerSupervisor>(),
            backendConnectPipeline: backendPipeline);
    }

    // ── E2E 1: Recovery when blocking listener releases port ──────────────────────────────

    [Fact(Timeout = 5_000)]
    public async Task E2E_Recovery_When_BlockingListenerReleasesPort()
    {
        if (_sim.SkipReason is not null)
            Assert.Skip(_sim.SkipReason);

        int listenPort = PickFreePort();

        // Block the port before starting the supervisor.
        var blocker = new TcpListener(IPAddress.Any, listenPort);
        blocker.Start();

        await using var supervisor = BuildSimSupervisor(listenPort);
        using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(30));

        await supervisor.StartAsync(cts.Token);

        // Wait for first bind attempt to fail.
        await supervisor.WaitForInitialBindAttemptAsync(cts.Token);
        Assert.Equal(SupervisorState.Recovering, supervisor.Snapshot().State);

        // Release the port.
        blocker.Stop();

        // Poll for up to 3 s for the supervisor to bind.
        using var recoveryCts = new CancellationTokenSource(TimeSpan.FromSeconds(3));
        while (!recoveryCts.IsCancellationRequested)
        {
            if (supervisor.Snapshot().State == SupervisorState.Bound)
                break;
            await Task.Delay(50, TestContext.Current.CancellationToken);
        }

        Assert.Equal(SupervisorState.Bound, supervisor.Snapshot().State);

        // Verify the proxy actually serves traffic by connecting to it.
        using var client = new TcpClient();
        await client.ConnectAsync("127.0.0.1", listenPort, cts.Token);

        // Send a minimal FC03 request (read 1 register at address 0).
        var req = new byte[]
        {
            0x00, 0x01, // TxId
            0x00, 0x00, // ProtocolId
            0x00, 0x06, // Length (6)
            0x01,       // UnitId
            0x03,       // FC03
            0x00, 0x00, // Start address 0
            0x00, 0x01, // Qty 1
        };
        await client.GetStream().WriteAsync(req, cts.Token);

        // Read at least 9 bytes (7 header + 2 data minimum for FC03 with 1 register).
        var rsp = new byte[260];
        int read = 0;
        using var readCts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
        while (read < 9 && !readCts.IsCancellationRequested)
            read += await client.GetStream().ReadAsync(rsp.AsMemory(read), readCts.Token);

        // Verify we got a response with matching TxId.
        Assert.True(read >= 9, $"Expected ≥ 9 bytes, got {read}");
        Assert.Equal(0x00, rsp[0]); // TxId high
        Assert.Equal(0x01, rsp[1]); // TxId low

        await supervisor.StopAsync(cts.Token);
    }

    // ── E2E 2: RecoveryAttempts counter increments and is visible on Snapshot ─────────────

    [Fact(Timeout = 5_000)]
    public async Task E2E_RecoveryAttempts_CounterIncrements_Visible_OnSnapshot()
    {
        if (_sim.SkipReason is not null)
            Assert.Skip(_sim.SkipReason);

        int listenPort = PickFreePort();

        // Block the port so the supervisor enters recovery.
        var blocker = new TcpListener(IPAddress.Any, listenPort);
        blocker.Start();

        // Use short delays to get multiple recovery attempts quickly.
        var profile = new RecoveryProfile
        {
            InitialBackoffMs = [100, 100, 100],
            SteadyStateMs    = 100,
        };

        await using var supervisor = BuildSimSupervisor(listenPort, profile);
        using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(20));

        await supervisor.StartAsync(cts.Token);
        await supervisor.WaitForInitialBindAttemptAsync(cts.Token);

        // Wait for multiple recovery attempts to accumulate.
        await Task.Delay(600, TestContext.Current.CancellationToken); // ~6 × 100 ms attempts

        var snap = supervisor.Snapshot();
        Assert.Equal(SupervisorState.Recovering, snap.State);
        Assert.True(snap.RecoveryAttempts >= 2,
            $"Expected ≥ 2 recovery attempts after 600ms with 100ms backoff; got {snap.RecoveryAttempts}");
        Assert.NotNull(snap.LastBindError);

        // Release the port and verify recovery.
        blocker.Stop();

        using var recoveryCts = new CancellationTokenSource(TimeSpan.FromSeconds(3));
        while (!recoveryCts.IsCancellationRequested)
        {
            if (supervisor.Snapshot().State == SupervisorState.Bound)
                break;
            await Task.Delay(50, TestContext.Current.CancellationToken);
        }

        Assert.Equal(SupervisorState.Bound, supervisor.Snapshot().State);

        // RecoveryAttempts must still be the accumulated value (not reset to 0).
        var afterSnap = supervisor.Snapshot();
        Assert.True(afterSnap.RecoveryAttempts >= snap.RecoveryAttempts,
            $"RecoveryAttempts should accumulate; was {snap.RecoveryAttempts}, now {afterSnap.RecoveryAttempts}");

        // LastBindError should be cleared after a successful bind.
        Assert.Null(afterSnap.LastBindError);

        await supervisor.StopAsync(cts.Token);
    }
}