using System.Collections.Frozen;
using Mbproxy.Bcd;
using Mbproxy.Proxy;
using Mbproxy.Proxy.Multiplexing;
using Microsoft.Extensions.Logging.Abstractions;
using Shouldly;
using Xunit;

namespace Mbproxy.Tests.Proxy;

/// <summary>
/// Unit tests for the <see cref="TagValueCapture"/> recording hooks in
/// <see cref="BcdPduPipeline"/>. Verifies that an armed capture records raw PLC-side
/// and decoded client-side values, and — as a regression guard — that a disarmed or
/// absent capture leaves the rewrite behaviour byte-identical.
/// </summary>
[Trait("Category", "Unit")]
public sealed class BcdPduPipelineCaptureTests
{
    private static readonly BcdPduPipeline Pipeline = new();

    private static BcdTagMap BuildMap(params BcdTag[] tags)
    {
        var frozen = tags.ToDictionary(t => t.Address).ToFrozenDictionary();
        return frozen.Count > 0 ? new BcdTagMap(frozen) : BcdTagMap.Empty;
    }

    private static PerPlcContext MakeContext(TagValueCapture? capture, params BcdTag[] tags)
        => new()
        {
            PlcName  = "TestPLC",
            TagMap   = BuildMap(tags),
            Counters = new ProxyCounters(),
            Logger   = NullLogger.Instance,
            Capture  = capture,
        };

    private static InFlightRequest MakeInFlight(byte fc, ushort start, ushort qty)
        => new(1, fc, start, qty, Array.Empty<InterestedParty>(), DateTimeOffset.UtcNow);

    private static byte[] Fc03Response(params ushort[] regs)
    {
        var pdu = new byte[2 + regs.Length * 2];
        pdu[0] = 0x03;
        pdu[1] = (byte)(regs.Length * 2);
        for (int i = 0; i < regs.Length; i++)
        {
            pdu[2 + i * 2]     = (byte)(regs[i] >> 8);
            pdu[2 + i * 2 + 1] = (byte)(regs[i] & 0xFF);
        }
        return pdu;
    }

    private static byte[] Fc06Request(ushort address, ushort value)
        => [0x06, (byte)(address >> 8), (byte)(address & 0xFF), (byte)(value >> 8), (byte)(value & 0xFF)];

    private static byte[] Fc16Request(ushort start, params ushort[] regs)
    {
        var pdu = new byte[6 + regs.Length * 2];
        pdu[0] = 0x10;
        pdu[1] = (byte)(start >> 8);
        pdu[2] = (byte)(start & 0xFF);
        pdu[3] = (byte)((ushort)regs.Length >> 8);
        pdu[4] = (byte)(regs.Length & 0xFF);
        pdu[5] = (byte)(regs.Length * 2);
        for (int i = 0; i < regs.Length; i++)
        {
            pdu[6 + i * 2]     = (byte)(regs[i] >> 8);
            pdu[6 + i * 2 + 1] = (byte)(regs[i] & 0xFF);
        }
        return pdu;
    }

    private static void ProcessFc03Response(PerPlcContext ctx, ushort start, ushort qty, byte[] response)
    {
        var responseCtx = ctx.WithCurrentRequest(MakeInFlight(0x03, start, qty));
        Pipeline.Process(MbapDirection.ResponseToClient, ReadOnlySpan<byte>.Empty, response.AsSpan(), responseCtx);
    }

    private static ushort ReadReg(byte[] pdu, int offsetWords)
        => (ushort)((pdu[2 + offsetWords * 2] << 8) | pdu[2 + offsetWords * 2 + 1]);

    // ── Read path (FC03/FC04 response) ───────────────────────────────────────

    [Fact]
    public void FC03_16Bit_ArmedCapture_RecordsRawAndDecoded()
    {
        var capture = new TagValueCapture([BcdTag.Create(100, 16)]);
        capture.Arm();
        var ctx = MakeContext(capture, BcdTag.Create(100, 16));

        ProcessFc03Response(ctx, 100, 1, Fc03Response(0x1234));

        var slot = capture.Snapshot().ShouldHaveSingleItem();
        slot.Address.ShouldBe((ushort)100);
        slot.RawLow.ShouldBe((ushort)0x1234);     // BCD nibbles on the PLC wire
        slot.DecodedValue.ShouldBe(1234);         // binary the client receives
        slot.Direction.ShouldBe(CaptureDirection.Read);
        slot.UpdatedAtUtc.ShouldNotBeNull();
    }

    [Fact]
    public void FC03_32Bit_ArmedCapture_RecordsBothRawWords()
    {
        var capture = new TagValueCapture([BcdTag.Create(100, 32)]);
        capture.Arm();
        var ctx = MakeContext(capture, BcdTag.Create(100, 32));

        // CDAB: low word 0x5678, high word 0x1234 → decoded 1234*10000 + 5678.
        ProcessFc03Response(ctx, 100, 2, Fc03Response(0x5678, 0x1234));

        var slot = capture.Snapshot().ShouldHaveSingleItem();
        slot.Width.ShouldBe((byte)32);
        slot.RawLow.ShouldBe((ushort)0x5678);
        slot.RawHigh.ShouldBe((ushort)0x1234);
        slot.DecodedValue.ShouldBe(12345678);
        slot.Direction.ShouldBe(CaptureDirection.Read);
    }

    // ── Write path (FC06 / FC16 request) ─────────────────────────────────────

    [Fact]
    public void FC06_ArmedCapture_RecordsEncodedBcdAndClientValue()
    {
        var capture = new TagValueCapture([BcdTag.Create(100, 16)]);
        capture.Arm();
        var ctx = MakeContext(capture, BcdTag.Create(100, 16));

        // Client writes binary 1234; proxy encodes to BCD 0x1234 for the PLC.
        var req = Fc06Request(100, 1234);
        Pipeline.Process(MbapDirection.RequestToBackend, ReadOnlySpan<byte>.Empty, req.AsSpan(), ctx);

        var slot = capture.Snapshot().ShouldHaveSingleItem();
        slot.RawLow.ShouldBe((ushort)0x1234);     // BCD nibbles sent to the PLC
        slot.DecodedValue.ShouldBe(1234);         // binary the client wrote
        slot.Direction.ShouldBe(CaptureDirection.Write);
    }

    [Fact]
    public void FC16_16Bit_ArmedCapture_RecordsWrite()
    {
        var capture = new TagValueCapture([BcdTag.Create(100, 16)]);
        capture.Arm();
        var ctx = MakeContext(capture, BcdTag.Create(100, 16));

        var req = Fc16Request(100, 4321);
        Pipeline.Process(MbapDirection.RequestToBackend, ReadOnlySpan<byte>.Empty, req.AsSpan(), ctx);

        var slot = capture.Snapshot().ShouldHaveSingleItem();
        slot.RawLow.ShouldBe((ushort)0x4321);
        slot.DecodedValue.ShouldBe(4321);
        slot.Direction.ShouldBe(CaptureDirection.Write);
    }

    // ── Regression guards: disarmed / absent capture ─────────────────────────

    [Fact]
    public void FC03_DisarmedCapture_StillRewrites_ButCapturesNothing()
    {
        var capture = new TagValueCapture([BcdTag.Create(100, 16)]);
        // Not armed.
        var ctx = MakeContext(capture, BcdTag.Create(100, 16));

        var rsp = Fc03Response(0x1234);
        ProcessFc03Response(ctx, 100, 1, rsp);

        ReadReg(rsp, 0).ShouldBe((ushort)1234);   // rewrite still happened
        capture.Snapshot().ShouldHaveSingleItem().UpdatedAtUtc.ShouldBeNull();
    }

    [Fact]
    public void FC03_NullCapture_DoesNotThrow_AndStillRewrites()
    {
        var ctx = MakeContext(capture: null, BcdTag.Create(100, 16));

        var rsp = Fc03Response(0x1234);
        Should.NotThrow(() => ProcessFc03Response(ctx, 100, 1, rsp));

        ReadReg(rsp, 0).ShouldBe((ushort)1234);
    }
}