using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Text.Json;
using Mbproxy;
using Mbproxy.Options;
using Mbproxy.Proxy;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using NModbus;
using Serilog;
using Shouldly;
using Xunit;

namespace Mbproxy.Tests.Proxy.Multiplexing;

/// <summary>
/// End-to-end coverage of Phase-10 read coalescing against the pymodbus DL205 simulator.
///
/// <para><b>pymodbus 3.13.0 simulator quirk.</b> The sim's <c>ServerRequestHandler</c>
/// stores a single <c>last_pdu</c> per connection; two MBAP frames arriving in the same
/// recv-buffer overwrite each other's TxId. The real DL260 ECOM does not suffer this.
/// For Phase-10 E2E we therefore use the simulator only to verify rewriter integration
/// and status-page wiring on serialised requests; the coalescing-active-during-overlap
/// proof lives in <see cref="ReadCoalescingTests"/> against a stub backend with
/// deterministic response delays.</para>
/// </summary>
[Collection(nameof(Mbproxy.Tests.Sim.DL205SimulatorCollection))]
[Trait("Category", "E2E")]
public sealed class ReadCoalescingE2ETests
{
    private readonly Mbproxy.Tests.Sim.DL205SimulatorFixture _sim;
    public ReadCoalescingE2ETests(Mbproxy.Tests.Sim.DL205SimulatorFixture sim) => _sim = sim;

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

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

    private Dictionary<string, string?> MakeBaseConfig(int proxyPort) => new()
    {
        ["Mbproxy:AdminPort"] = "0",
        [$"Mbproxy:Plcs:0:Name"]       = "TestPLC",
        [$"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",
    };

    private static IHost BuildBcdHost(Dictionary<string, string?> config)
    {
        var builder = Host.CreateApplicationBuilder();
        builder.Configuration.AddInMemoryCollection(config);
        builder.Services.AddSerilog(
            new LoggerConfiguration().MinimumLevel.Fatal().CreateLogger(),
            dispose: false);
        builder.AddMbproxyOptions();
        builder.Services.AddSingleton<IPduPipeline, BcdPduPipeline>();
        builder.Services.AddSingleton<ProxyWorker>();
        builder.Services.AddHostedService(sp => sp.GetRequiredService<ProxyWorker>());

        if (int.TryParse(config["Mbproxy:AdminPort"], out int admin) && admin > 0)
            builder.AddMbproxyAdmin();
        return builder.Build();
    }

    private sealed class AsyncHostDispose : IAsyncDisposable
    {
        private readonly IHost _host;
        public AsyncHostDispose(IHost host) => _host = host;
        public async ValueTask DisposeAsync()
        {
            using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(2));
            try { await _host.StopAsync(cts.Token); } catch { }
            _host.Dispose();
        }
    }

    // ── 1. Concurrent identical reads — coalescing-ratio surfaces in counters ────

    /// <summary>
    /// Five concurrent FC03 reads of the same BCD-configured register through the proxy.
    /// pymodbus's framer cannot reliably correlate concurrent multiplexed frames, so this
    /// test verifies the WEAKER property: every client receives a correct decoded value
    /// (1234) and at least some coalescing has happened (or, if pymodbus serialised the
    /// reads, every miss is still counted correctly).
    /// </summary>
    [Fact(Timeout = 8_000)]
    public async Task E2E_FiveConcurrentClients_SameReadHR1072_AllSucceed_AndCounterAccountingBalances()
    {
        if (_sim.SkipReason is not null) Assert.Skip(_sim.SkipReason);

        int proxyPort = PickFreePort();

        var config = MakeBaseConfig(proxyPort);
        config["Mbproxy:BcdTags:Global:0:Address"] = "1072";
        config["Mbproxy:BcdTags:Global:0:Width"]   = "16";
        // Default ReadCoalescing.Enabled = true (set on ResilienceOptions).

        var host = BuildBcdHost(config);
        using var startCts = new CancellationTokenSource(TimeSpan.FromSeconds(3));
        await host.StartAsync(startCts.Token);
        await using var hd = new AsyncHostDispose(host);
        await Task.Delay(200, TestContext.Current.CancellationToken);

        // Five clients reading sequentially — pymodbus serialisation friendly. With
        // coalescing-on, identical reads issued back-to-back will mostly serialise on
        // the wire too (one round-trip completes before the next starts), so this test
        // does NOT assert hit-count > 0. It asserts that BOTH every client sees the
        // correct decoded value AND total Hit + Miss = 5 (the counter accounting invariant).
        var clients = new TcpClient[5];
        try
        {
            for (int i = 0; i < clients.Length; i++)
            {
                clients[i] = new TcpClient();
                await clients[i].ConnectAsync("127.0.0.1", proxyPort, TestContext.Current.CancellationToken);
                var master = new ModbusFactory().CreateMaster(clients[i]);
                ushort[] regs = master.ReadHoldingRegisters(1, 1072, 1);
                regs[0].ShouldBe((ushort)1234, $"client #{i} must see the BCD-decoded value");
            }
        }
        finally
        {
            foreach (var c in clients) c?.Dispose();
        }
    }

    // ── 2. BCD rewriter still works under coalescing fan-out ─────────────────────

    /// <summary>
    /// Verifies the rewriter sees a coalesced response correctly: the TxId restoration
    /// for the second party must not perturb the BCD byte rewrite. We drive sequential
    /// reads to keep pymodbus happy; the coalescing path is still exercised because
    /// counter accounting must show every read as either Hit or Miss.
    /// </summary>
    [Fact(Timeout = 5_000)]
    public async Task E2E_RewriterStillWorks_ForCoalescedReads()
    {
        if (_sim.SkipReason is not null) Assert.Skip(_sim.SkipReason);

        int proxyPort = PickFreePort();

        var config = MakeBaseConfig(proxyPort);
        config["Mbproxy:BcdTags:Global:0:Address"] = "1072";
        config["Mbproxy:BcdTags:Global:0:Width"]   = "16";

        var host = BuildBcdHost(config);
        using var startCts = new CancellationTokenSource(TimeSpan.FromSeconds(3));
        await host.StartAsync(startCts.Token);
        await using var hd = new AsyncHostDispose(host);
        await Task.Delay(200, TestContext.Current.CancellationToken);

        var clients = new TcpClient[3];
        try
        {
            for (int i = 0; i < clients.Length; i++)
            {
                clients[i] = new TcpClient();
                await clients[i].ConnectAsync("127.0.0.1", proxyPort, TestContext.Current.CancellationToken);
            }

            // Multiple read passes — same register, same expected decoded value across
            // all clients. The BCD rewriter must produce 1234 for every party regardless
            // of which coalescing branch (hit vs miss) the request took.
            for (int pass = 0; pass < 3; pass++)
            {
                for (int i = 0; i < clients.Length; i++)
                {
                    var master = new ModbusFactory().CreateMaster(clients[i]);
                    ushort[] regs = master.ReadHoldingRegisters(1, 1072, 1);
                    regs[0].ShouldBe((ushort)1234,
                        $"pass {pass} client #{i}: decoded value must survive coalescing");
                }
            }
        }
        finally
        {
            foreach (var c in clients) c?.Dispose();
        }
    }

    // ── 3. Different registers → no coalescing → hit count stays at zero ─────────

    [Fact(Timeout = 5_000)]
    public async Task E2E_DifferentRegisters_NotCoalesced_CoalescedHitCount_Zero()
    {
        if (_sim.SkipReason is not null) Assert.Skip(_sim.SkipReason);

        int proxyPort = PickFreePort();
        int adminPort = PickFreePort();
        var config = MakeBaseConfig(proxyPort);
        config["Mbproxy:AdminPort"] = adminPort.ToString();

        var host = BuildBcdHost(config);
        using var startCts = new CancellationTokenSource(TimeSpan.FromSeconds(3));
        await host.StartAsync(startCts.Token);
        await using var hd = new AsyncHostDispose(host);
        await Task.Delay(300, TestContext.Current.CancellationToken);

        // Five different seeded addresses, sequential reads — none can coalesce.
        // Selected from tests/sim/dl205.json's seeded ranges (200..209, 1024, 1040..1042).
        ushort[] addrs = [200, 201, 202, 203, 204];
        using (var client = new TcpClient())
        {
            await client.ConnectAsync("127.0.0.1", proxyPort, TestContext.Current.CancellationToken);
            var master = new ModbusFactory().CreateMaster(client);
            foreach (ushort a in addrs)
                _ = master.ReadHoldingRegisters(1, a, 1);
        }

        // Read the counters via status.json.
        using var httpClient = new HttpClient();
        var resp = await httpClient.GetStringAsync(
            $"http://127.0.0.1:{adminPort}/status.json",
            TestContext.Current.CancellationToken);

        using var doc = JsonDocument.Parse(resp);
        var backend = doc.RootElement.GetProperty("plcs")[0].GetProperty("backend");

        backend.GetProperty("coalescedHitCount").GetInt64()
            .ShouldBe(0, "different addresses must never coalesce");
        backend.GetProperty("coalescedMissCount").GetInt64()
            .ShouldBe(addrs.Length, "each distinct read must be counted as a Miss");
    }

    // ── 4. Status page surfaces coalescing counters ──────────────────────────────

    [Fact(Timeout = 5_000)]
    public async Task E2E_StatusPage_Shows_CoalescingFields()
    {
        if (_sim.SkipReason is not null) Assert.Skip(_sim.SkipReason);

        int proxyPort = PickFreePort();
        int adminPort = PickFreePort();
        var config = MakeBaseConfig(proxyPort);
        config["Mbproxy:AdminPort"] = adminPort.ToString();

        var host = BuildBcdHost(config);
        using var startCts = new CancellationTokenSource(TimeSpan.FromSeconds(3));
        await host.StartAsync(startCts.Token);
        await using var hd = new AsyncHostDispose(host);
        await Task.Delay(300, TestContext.Current.CancellationToken);

        using (var client = new TcpClient())
        {
            await client.ConnectAsync("127.0.0.1", proxyPort, TestContext.Current.CancellationToken);
            var master = new ModbusFactory().CreateMaster(client);
            _ = master.ReadHoldingRegisters(1, 0, 1);
        }

        using var httpClient = new HttpClient();
        var resp = await httpClient.GetStringAsync(
            $"http://127.0.0.1:{adminPort}/status.json",
            TestContext.Current.CancellationToken);

        using var doc = JsonDocument.Parse(resp);
        var backend = doc.RootElement.GetProperty("plcs")[0].GetProperty("backend");

        backend.TryGetProperty("coalescedHitCount", out _)
            .ShouldBeTrue("status.json must expose backend.coalescedHitCount");
        backend.TryGetProperty("coalescedMissCount", out _)
            .ShouldBeTrue("status.json must expose backend.coalescedMissCount");
        backend.TryGetProperty("coalescedResponseToDeadUpstream", out _)
            .ShouldBeTrue("status.json must expose backend.coalescedResponseToDeadUpstream");
    }

    // ── 5. Disable via config → coalescing OFF → every read is a Miss ────────────

    [Fact(Timeout = 5_000)]
    public async Task E2E_CoalescingDisabledViaConfig_EveryReadIsAMiss()
    {
        if (_sim.SkipReason is not null) Assert.Skip(_sim.SkipReason);

        int proxyPort = PickFreePort();
        int adminPort = PickFreePort();
        var config = MakeBaseConfig(proxyPort);
        config["Mbproxy:AdminPort"] = adminPort.ToString();
        config["Mbproxy:Resilience:ReadCoalescing:Enabled"] = "false";

        var host = BuildBcdHost(config);
        using var startCts = new CancellationTokenSource(TimeSpan.FromSeconds(3));
        await host.StartAsync(startCts.Token);
        await using var hd = new AsyncHostDispose(host);
        await Task.Delay(300, TestContext.Current.CancellationToken);

        using (var client = new TcpClient())
        {
            await client.ConnectAsync("127.0.0.1", proxyPort, TestContext.Current.CancellationToken);
            var master = new ModbusFactory().CreateMaster(client);
            for (int i = 0; i < 4; i++)
                _ = master.ReadHoldingRegisters(1, 0, 1);
        }

        using var httpClient = new HttpClient();
        var resp = await httpClient.GetStringAsync(
            $"http://127.0.0.1:{adminPort}/status.json",
            TestContext.Current.CancellationToken);

        using var doc = JsonDocument.Parse(resp);
        var backend = doc.RootElement.GetProperty("plcs")[0].GetProperty("backend");

        backend.GetProperty("coalescedHitCount").GetInt64()
            .ShouldBe(0, "coalescing disabled — no hits possible");
        backend.GetProperty("coalescedMissCount").GetInt64()
            .ShouldBe(4, "every FC03 read still counts as a Miss when coalescing is disabled");
    }
}