using System.Collections.Concurrent;
using System.Net;
using System.Net.Sockets;
using Mbproxy;
using Mbproxy.Proxy;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using NModbus;
using Serilog;
using Serilog.Core;
using Serilog.Events;
using Shouldly;
using Xunit;

namespace Mbproxy.Tests.Proxy;

/// <summary>
/// End-to-end tests for the BCD rewriter pipeline against the pymodbus DL205 simulator.
///
/// Each test starts an in-process proxy host configured to point at the simulator,
/// connects an NModbus client to the proxy's listen port, and asserts bidirectional
/// BCD rewriting behaviour.
///
/// All tests skip gracefully when the simulator is unavailable (Python / pymodbus missing).
/// </summary>
[Collection(nameof(Mbproxy.Tests.Sim.DL205SimulatorCollection))]
[Trait("Category", "E2E")]
public sealed class RewriterE2ETests
{
    private readonly Mbproxy.Tests.Sim.DL205SimulatorFixture _sim;

    public RewriterE2ETests(Mbproxy.Tests.Sim.DL205SimulatorFixture sim)
    {
        _sim = sim;
    }

    // ── 1. FC03 HR1072 with BCD configured → decoded 1234 ────────────────────

    /// <summary>
    /// Configure a 16-bit BCD tag at address 1072 (seeded 0x1234 in the simulator).
    /// The proxy should decode the BCD nibbles and return binary 1234 to the client.
    /// </summary>
    [Fact(Timeout = 5_000)]
    public async Task Read_HR1072_AsBcd_ReturnsDecoded_1234()
    {
        if (_sim.SkipReason is not null)
            Assert.Skip(_sim.SkipReason);

        var (proxyPort, host, cts) = await StartBcdProxyAsync(bcd16Addresses: [1072]);
        await using var _ = new AsyncHostDispose(host, cts);

        using var client = new TcpClient();
        await client.ConnectAsync("127.0.0.1", proxyPort, TestContext.Current.CancellationToken);
        var master = new ModbusFactory().CreateMaster(client);

        ushort[] regs = master.ReadHoldingRegisters(slaveAddress: 1, startAddress: 1072, numberOfPoints: 1);

        // Simulator stores 0x1234 = raw BCD. Proxy should decode → 1234 decimal.
        regs[0].ShouldBe((ushort)1234);
    }

    // ── 2. FC03 HR1072 without BCD configured → raw 0x1234 ───────────────────

    /// <summary>
    /// Same address, no BCD tags configured. The proxy passes the raw BCD nibbles through.
    /// Verifies the rewriter is opt-in per tag.
    /// </summary>
    [Fact(Timeout = 5_000)]
    public async Task Read_HR1072_AsRaw_WhenNotConfigured_Returns_0x1234()
    {
        if (_sim.SkipReason is not null)
            Assert.Skip(_sim.SkipReason);

        // Empty BCD tag list — no rewriting.
        var (proxyPort, host, cts) = await StartBcdProxyAsync(bcd16Addresses: []);
        await using var _ = new AsyncHostDispose(host, cts);

        using var client = new TcpClient();
        await client.ConnectAsync("127.0.0.1", proxyPort, TestContext.Current.CancellationToken);
        var master = new ModbusFactory().CreateMaster(client);

        ushort[] regs = master.ReadHoldingRegisters(slaveAddress: 1, startAddress: 1072, numberOfPoints: 1);

        // Raw BCD nibbles pass through unchanged.
        regs[0].ShouldBe((ushort)0x1234);
    }

    // ── 3. FC06 write BCD → simulator stores encoded nibbles ────────────────

    /// <summary>
    /// Configure a 16-bit BCD tag at address 200 (in the simulator's writable scratch range).
    /// Write decimal 9876 through the proxy; read back raw from the simulator and expect 0x9876.
    /// </summary>
    [Fact(Timeout = 5_000)]
    public async Task Write_HR200_AsBcd_StoresEncoded_0x9876()
    {
        if (_sim.SkipReason is not null)
            Assert.Skip(_sim.SkipReason);

        var (proxyPort, host, cts) = await StartBcdProxyAsync(bcd16Addresses: [200]);
        await using var _ = new AsyncHostDispose(host, cts);

        // Write through the proxy (client side: binary 9876).
        using var proxyClient = new TcpClient();
        await proxyClient.ConnectAsync("127.0.0.1", proxyPort, TestContext.Current.CancellationToken);
        var proxyMaster = new ModbusFactory().CreateMaster(proxyClient);
        proxyMaster.WriteSingleRegister(slaveAddress: 1, registerAddress: 200, value: 9876);

        // Read raw from the simulator directly (bypassing the proxy).
        using var simClient = new TcpClient();
        await simClient.ConnectAsync(_sim.Host, _sim.Port, TestContext.Current.CancellationToken);
        var simMaster = new ModbusFactory().CreateMaster(simClient);
        ushort[] raw = simMaster.ReadHoldingRegisters(slaveAddress: 1, startAddress: 200, numberOfPoints: 1);

        // Simulator should store BCD-encoded 9876 = 0x9876.
        raw[0].ShouldBe((ushort)0x9876);
    }

    // ── 4. FC03 read 32-bit BCD pair at HR1072/HR1073 (CDAB) ────────────────

    /// <summary>
    /// Reads a 32-bit BCD pair at address 1072/1073 (CDAB layout).
    /// Simulator seeds: 1072=0x1234 (low word), 1073=0x0000 (high word).
    /// Decoded = 0*10000 + 1234 = 1234.
    /// This verifies the CDAB word order is handled end-to-end.
    /// </summary>
    [Fact(Timeout = 5_000)]
    public async Task Read_HR1072_HR1073_AsBcd32_ReturnsDecoded_From_CDAB()
    {
        if (_sim.SkipReason is not null)
            Assert.Skip(_sim.SkipReason);

        var (proxyPort, host, cts) = await StartBcdProxyAsync(bcd32Addresses: [1072]);
        await using var _ = new AsyncHostDispose(host, cts);

        using var client = new TcpClient();
        await client.ConnectAsync("127.0.0.1", proxyPort, TestContext.Current.CancellationToken);
        var master = new ModbusFactory().CreateMaster(client);

        // Read both registers of the 32-bit pair.
        ushort[] regs = master.ReadHoldingRegisters(slaveAddress: 1, startAddress: 1072, numberOfPoints: 2);

        // After decoding: low 4 digits = 1234, high 4 digits = 0
        // The proxy returns decoded binary values in CDAB order:
        // regs[0] = low 4 decoded digits = 1234
        // regs[1] = high 4 decoded digits = 0
        regs[0].ShouldBe((ushort)1234); // decoded low 4 digits
        regs[1].ShouldBe((ushort)0);    // decoded high 4 digits
    }

    // ── 5. Partial FC03 on high register of 32-bit pair → raw + warning ──────

    /// <summary>
    /// Read only the high register (1073) of a 32-bit BCD pair at 1072/1073.
    /// The proxy cannot decode a partial pair — it should pass through raw and log
    /// mbproxy.rewrite.partial_bcd.
    /// </summary>
    [Fact(Timeout = 5_000)]
    public async Task Partial_FC03_OnHighRegisterOf_32BitPair_PassesThroughRaw_AndLogsWarning()
    {
        if (_sim.SkipReason is not null)
            Assert.Skip(_sim.SkipReason);

        var sink = new CapturingSink();
        var serilog = new LoggerConfiguration()
            .MinimumLevel.Warning()
            .WriteTo.Sink(sink)
            .CreateLogger();

        var (proxyPort, host, cts) = await StartBcdProxyAsync(
            bcd32Addresses: [1072],
            serilogOverride: serilog);
        await using var _ = new AsyncHostDispose(host, cts);

        using var client = new TcpClient();
        await client.ConnectAsync("127.0.0.1", proxyPort, TestContext.Current.CancellationToken);
        var master = new ModbusFactory().CreateMaster(client);

        // Read only the high register (1073) — partial overlap for the 32-bit pair.
        ushort[] regs = master.ReadHoldingRegisters(slaveAddress: 1, startAddress: 1073, numberOfPoints: 1);

        // The raw simulator value for HR1073 is 0x0000 (high word of the 32-bit pair).
        regs[0].ShouldBe((ushort)0x0000); // raw passthrough

        // The partial_bcd warning should have been logged.
        var partialEvents = sink.Events
            .Where(e => e.MessageTemplate.Text.Contains("mbproxy.rewrite.partial_bcd")
                     || e.MessageTemplate.Text.Contains("Partial BCD overlap"))
            .ToList();
        partialEvents.ShouldNotBeEmpty("Expected mbproxy.rewrite.partial_bcd warning to be logged");
    }

    // ── 6. MBAP TxId preserved after rewriting (20 consecutive) ─────────────

    /// <summary>
    /// Issues 20 consecutive FC03 reads with manually-incremented TxIds through a proxy
    /// that has BCD rewriting active (tag at 1072). Verifies the MBAP header is never
    /// tampered with by the rewriter.
    /// </summary>
    [Fact(Timeout = 5_000)]
    public async Task MbapTxId_StillPreserved_AfterRewriting_20Consecutive()
    {
        if (_sim.SkipReason is not null)
            Assert.Skip(_sim.SkipReason);

        var (proxyPort, host, cts) = await StartBcdProxyAsync(bcd16Addresses: [1072]);
        await using var _ = new AsyncHostDispose(host, cts);

        using var socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        socket.NoDelay = true;
        await socket.ConnectAsync("127.0.0.1", proxyPort, TestContext.Current.CancellationToken);

        const int count = 20;
        byte[] reqBuf = new byte[12]; // FC03 request frame
        byte[] rspBuf = new byte[260];

        for (ushort txId = 1; txId <= count; txId++)
        {
            // Build FC03 request: read 1 register at address 1072.
            reqBuf[0] = (byte)(txId >> 8);
            reqBuf[1] = (byte)(txId & 0xFF);
            reqBuf[2] = 0x00;
            reqBuf[3] = 0x00;
            reqBuf[4] = 0x00;
            reqBuf[5] = 0x06; // Length
            reqBuf[6] = 0x01; // UnitId
            reqBuf[7] = 0x03; // FC03
            reqBuf[8] = 0x04; // Start addr high (1072 = 0x0430)
            reqBuf[9] = 0x30; // Start addr low
            reqBuf[10] = 0x00;
            reqBuf[11] = 0x01; // Qty = 1

            await socket.SendAsync(reqBuf.AsMemory(), SocketFlags.None, TestContext.Current.CancellationToken);

            // Read 7-byte response header.
            int read = 0;
            while (read < 7)
                read += await socket.ReceiveAsync(rspBuf.AsMemory(read, 7 - read), SocketFlags.None,
                    TestContext.Current.CancellationToken);

            ushort rspTxId  = (ushort)((rspBuf[0] << 8) | rspBuf[1]);
            ushort rspLength = (ushort)((rspBuf[4] << 8) | rspBuf[5]);

            rspTxId.ShouldBe(txId, $"TxId mismatch on iteration {txId}");

            // Drain the body.
            int bodyLen = rspLength - 1;
            if (bodyLen > 0)
            {
                int bodyRead = 0;
                while (bodyRead < bodyLen)
                    bodyRead += await socket.ReceiveAsync(rspBuf.AsMemory(7 + bodyRead, bodyLen - bodyRead),
                        SocketFlags.None, TestContext.Current.CancellationToken);
            }
        }
    }

    // ── 7. FC16 with 16-bit BCD in middle of write range ────────────────────

    /// <summary>
    /// FC16 (Write Multiple Registers) covering a 3-register span where only the middle
    /// register is a configured BCD tag. The proxy must encode the middle slot and leave
    /// the flanks untouched. Verifies per-register selectivity within a multi-register write.
    /// </summary>
    [Fact(Timeout = 5_000)]
    public async Task Write_FC16_With_Bcd16_InRange_StoresEncoded_AtOnlyTheBcdSlot()
    {
        if (_sim.SkipReason is not null)
            Assert.Skip(_sim.SkipReason);

        // Configure a 16-bit BCD tag at the middle register of a 3-register write.
        var (proxyPort, host, cts) = await StartBcdProxyAsync(bcd16Addresses: [205]);
        await using var _ = new AsyncHostDispose(host, cts);

        // FC16 write to HR204..HR206 with binary values [10, 9876, 20].
        using var proxyClient = new TcpClient();
        await proxyClient.ConnectAsync("127.0.0.1", proxyPort, TestContext.Current.CancellationToken);
        var proxyMaster = new ModbusFactory().CreateMaster(proxyClient);
        proxyMaster.WriteMultipleRegisters(slaveAddress: 1, startAddress: 204,
            data: new ushort[] { 10, 9876, 20 });

        // Read raw from the simulator directly.
        using var simClient = new TcpClient();
        await simClient.ConnectAsync(_sim.Host, _sim.Port, TestContext.Current.CancellationToken);
        var simMaster = new ModbusFactory().CreateMaster(simClient);
        ushort[] raw = simMaster.ReadHoldingRegisters(slaveAddress: 1, startAddress: 204, numberOfPoints: 3);

        raw[0].ShouldBe((ushort)10,     "HR204 is not a BCD tag — must pass through unchanged");
        raw[1].ShouldBe((ushort)0x9876, "HR205 is a 16-bit BCD tag — must be re-encoded to nibbles");
        raw[2].ShouldBe((ushort)20,     "HR206 is not a BCD tag — must pass through unchanged");
    }

    // ── 8. FC16 with 32-bit BCD pair → both halves CDAB-encoded ─────────────

    /// <summary>
    /// FC16 covering both halves of a configured 32-bit BCD pair. The pipeline reconstructs
    /// the binary integer from the CDAB-ordered registers (binaryValue = high * 10000 + low),
    /// encodes it as a BCD pair, and writes back in CDAB order.
    ///
    /// Example: client writes [low=5678, high=1234] → binaryValue = 12345678
    ///        → Encode32(12345678) = (bcdLow=0x5678, bcdHigh=0x1234)
    /// </summary>
    [Fact(Timeout = 5_000)]
    public async Task Write_FC16_With_Bcd32Pair_StoresCdabEncoded()
    {
        if (_sim.SkipReason is not null)
            Assert.Skip(_sim.SkipReason);

        // Configure a 32-bit BCD tag spanning HR207 + HR208 (both in [200, 209] scratch range).
        var (proxyPort, host, cts) = await StartBcdProxyAsync(bcd32Addresses: [207]);
        await using var _ = new AsyncHostDispose(host, cts);

        // FC16 write of [low=5678, high=1234] → decimal 12345678.
        using var proxyClient = new TcpClient();
        await proxyClient.ConnectAsync("127.0.0.1", proxyPort, TestContext.Current.CancellationToken);
        var proxyMaster = new ModbusFactory().CreateMaster(proxyClient);
        proxyMaster.WriteMultipleRegisters(slaveAddress: 1, startAddress: 207,
            data: new ushort[] { 5678, 1234 });

        using var simClient = new TcpClient();
        await simClient.ConnectAsync(_sim.Host, _sim.Port, TestContext.Current.CancellationToken);
        var simMaster = new ModbusFactory().CreateMaster(simClient);
        ushort[] raw = simMaster.ReadHoldingRegisters(slaveAddress: 1, startAddress: 207, numberOfPoints: 2);

        raw[0].ShouldBe((ushort)0x5678, "HR207 (low word of CDAB pair) must hold low 4 BCD digits");
        raw[1].ShouldBe((ushort)0x1234, "HR208 (high word of CDAB pair) must hold high 4 BCD digits");
    }

    // ── 9. FC16 partial overlap on 32-bit pair → raw + warning ──────────────

    /// <summary>
    /// FC16 writes only the LOW register of a configured 32-bit BCD pair (qty=1 at the low
    /// address). The pipeline cannot safely encode half of a 32-bit value, so it passes the
    /// register through raw and logs mbproxy.rewrite.partial_bcd.
    /// </summary>
    [Fact(Timeout = 5_000)]
    public async Task Write_FC16_PartialBcd32_OnLowAddressOnly_PassesThroughRaw_AndLogsWarning()
    {
        if (_sim.SkipReason is not null)
            Assert.Skip(_sim.SkipReason);

        var sink = new CapturingSink();
        var serilog = new LoggerConfiguration()
            .MinimumLevel.Warning()
            .WriteTo.Sink(sink)
            .CreateLogger();

        // Configure a 32-bit BCD tag at HR207 + HR208 (pair).
        var (proxyPort, host, cts) = await StartBcdProxyAsync(
            bcd32Addresses: [207],
            serilogOverride: serilog);
        await using var _ = new AsyncHostDispose(host, cts);

        // FC16 write of [42] to HR207 only — partial overlap on the 32-bit pair.
        using var proxyClient = new TcpClient();
        await proxyClient.ConnectAsync("127.0.0.1", proxyPort, TestContext.Current.CancellationToken);
        var proxyMaster = new ModbusFactory().CreateMaster(proxyClient);
        proxyMaster.WriteMultipleRegisters(slaveAddress: 1, startAddress: 207,
            data: new ushort[] { 42 });

        // Simulator should hold the raw value 42 (no rewriting on partial overlap).
        using var simClient = new TcpClient();
        await simClient.ConnectAsync(_sim.Host, _sim.Port, TestContext.Current.CancellationToken);
        var simMaster = new ModbusFactory().CreateMaster(simClient);
        ushort[] raw = simMaster.ReadHoldingRegisters(slaveAddress: 1, startAddress: 207, numberOfPoints: 1);
        raw[0].ShouldBe((ushort)42, "Partial-overlap write must pass through raw (not BCD-encoded)");

        // The partial_bcd warning must have been logged.
        var partialEvents = sink.Events
            .Where(e => e.MessageTemplate.Text.Contains("mbproxy.rewrite.partial_bcd")
                     || e.MessageTemplate.Text.Contains("Partial BCD overlap"))
            .ToList();
        partialEvents.ShouldNotBeEmpty("Expected mbproxy.rewrite.partial_bcd warning on partial FC16 write");
    }

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

    private async Task<(int proxyPort, IHost host, CancellationTokenSource cts)> StartBcdProxyAsync(
        ushort[]? bcd16Addresses = null,
        ushort[]? bcd32Addresses = null,
        Serilog.ILogger? serilogOverride = null)
    {
        int proxyPort = PickFreePort();

        var config = new Dictionary<string, string?>
        {
            ["Mbproxy:AdminPort"] = "8080",
            ["Mbproxy:Plcs:0:Name"]       = "TestPLC",
            ["Mbproxy:Plcs:0:ListenPort"] = proxyPort.ToString(),
            ["Mbproxy:Plcs:0:Host"]       = _sim.Host,
            ["Mbproxy:Plcs:0:Port"]       = _sim.Port.ToString(),
            ["Mbproxy:Connection:BackendConnectTimeoutMs"] = "3000",
            ["Mbproxy:Connection:BackendRequestTimeoutMs"] = "3000",
        };

        // Add BCD tag entries to the in-memory config.
        int tagIndex = 0;
        foreach (ushort addr in bcd16Addresses ?? [])
        {
            config[$"Mbproxy:BcdTags:Global:{tagIndex}:Address"] = addr.ToString();
            config[$"Mbproxy:BcdTags:Global:{tagIndex}:Width"]   = "16";
            tagIndex++;
        }
        foreach (ushort addr in bcd32Addresses ?? [])
        {
            config[$"Mbproxy:BcdTags:Global:{tagIndex}:Address"] = addr.ToString();
            config[$"Mbproxy:BcdTags:Global:{tagIndex}:Width"]   = "32";
            tagIndex++;
        }

        using var startCts = new CancellationTokenSource(TimeSpan.FromSeconds(10));
        var host = BuildBcdProxyHost(config, serilogOverride);
        await host.StartAsync(startCts.Token);

        await Task.Delay(150, TestContext.Current.CancellationToken);

        var runCts = new CancellationTokenSource(TimeSpan.FromSeconds(30));
        return (proxyPort, host, runCts);
    }

    private static IHost BuildBcdProxyHost(
        Dictionary<string, string?> config,
        Serilog.ILogger? serilogOverride = null)
    {
        var builder = Host.CreateApplicationBuilder();
        builder.Configuration.AddInMemoryCollection(config);

        var logger = serilogOverride
            ?? new LoggerConfiguration().MinimumLevel.Fatal().CreateLogger();

        builder.Services.AddSerilog(logger, dispose: false);
        builder.AddMbproxyOptions();
        // Use the real BcdPduPipeline (not NoopPduPipeline) for E2E rewriter tests.
        builder.Services.AddSingleton<IPduPipeline, BcdPduPipeline>();
        builder.Services.AddHostedService<ProxyWorker>();
        return builder.Build();
    }

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

    private sealed class AsyncHostDispose : IAsyncDisposable
    {
        private readonly IHost _host;
        private readonly CancellationTokenSource _cts;

        public AsyncHostDispose(IHost host, CancellationTokenSource cts)
        {
            _host = host;
            _cts  = cts;
        }

        public async ValueTask DisposeAsync()
        {
            using var stopCts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
            try { await _host.StopAsync(stopCts.Token); } catch { /* best effort */ }
            _host.Dispose();
            _cts.Dispose();
        }
    }

    // ── Capturing log sink (shared with HostSmokeTests) ─────────────────────

    private sealed class CapturingSink : ILogEventSink
    {
        private readonly ConcurrentQueue<LogEvent> _events = new();
        public IEnumerable<LogEvent> Events => _events;
        public void Emit(LogEvent logEvent) => _events.Enqueue(logEvent);
    }
}