using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;

namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests;

/// <summary>
///     Issue #270, plan PR F4-c — <c>pmc_wrpmcrng</c> coverage. The driver-level
///     <c>Writes.AllowPmc</c> kill switch sits on top of the F4-a
///     <c>Writes.Enabled</c> + per-tag <c>Writable</c> opt-ins. PMC bit writes
///     additionally exercise the read-modify-write helper (<c>pmc_wrpmcrng</c> is
///     byte-addressed; the wire never sees a sub-byte write). PMC tags surface
///     <see cref="SecurityClassification.Operate"/> for the server-layer ACL gate.
/// </summary>
[Trait("Category", "Unit")]
public sealed class FocasWritePmcTests
{
    private const string Host = "focas://10.0.0.5:8193";

    private static FocasDriver NewDriver(
        FocasWritesOptions writes,
        FocasTagDefinition[] tags,
        out FakeFocasClientFactory factory)
    {
        factory = new FakeFocasClientFactory();
        return new FocasDriver(new FocasDriverOptions
        {
            Devices = [new FocasDeviceOptions(Host)],
            Tags = tags,
            Probe = new FocasProbeOptions { Enabled = false },
            Writes = writes,
        }, "drv-1", factory);
    }

    /// <summary>
    ///     Variant that pre-seeds a fake's PMC byte storage (so an RMW test can verify
    ///     the read-side picked up the prior byte before the bit mask). The customiser
    ///     fires once per device — sufficient for the single-device tests below.
    /// </summary>
    private static FocasDriver NewDriverWithSeededPmc(
        FocasWritesOptions writes,
        FocasTagDefinition[] tags,
        string letter,
        int pathId,
        byte[] seed,
        out FakeFocasClientFactory factory)
    {
        factory = new FakeFocasClientFactory
        {
            Customise = () =>
            {
                var c = new FakeFocasClient();
                c.PmcByteRanges[(letter.ToUpperInvariant(), pathId)] = (byte[])seed.Clone();
                return c;
            },
        };
        return new FocasDriver(new FocasDriverOptions
        {
            Devices = [new FocasDeviceOptions(Host)],
            Tags = tags,
            Probe = new FocasProbeOptions { Enabled = false },
            Writes = writes,
        }, "drv-1", factory);
    }

    [Fact]
    public async Task AllowPmc_false_returns_BadNotWritable_even_with_Enabled_and_Writable()
    {
        // F4-c — the granular kill switch defaults off so a redeployed driver with
        // Writes.Enabled=true still keeps PMC writes locked until the operator team
        // explicitly opts in. PMC is ladder working memory; defense-in-depth is
        // critical because a mistargeted bit can move motion or latch a feedhold.
        var drv = NewDriver(
            writes: new FocasWritesOptions { Enabled = true, AllowPmc = false },
            tags:
            [
                new FocasTagDefinition("Coil", Host, "R100", FocasDataType.Byte, Writable: true),
            ],
            out var factory);
        await drv.InitializeAsync("{}", CancellationToken.None);

        var results = await drv.WriteAsync(
            [new WriteRequest("Coil", (sbyte)42)], CancellationToken.None);

        results.Single().StatusCode.ShouldBe(FocasStatusMapper.BadNotWritable);
        // Wire client was never even constructed because the gate short-circuited
        // before EnsureConnectedAsync — defense in depth + lower blast radius.
        factory.Clients.ShouldBeEmpty();
    }

    [Fact]
    public async Task AllowPmc_true_byte_write_dispatches_to_typed_WritePmcRangeAsync()
    {
        var drv = NewDriver(
            writes: new FocasWritesOptions { Enabled = true, AllowPmc = true },
            tags:
            [
                new FocasTagDefinition("Coil", Host, "R100", FocasDataType.Byte, Writable: true),
            ],
            out var factory);
        await drv.InitializeAsync("{}", CancellationToken.None);

        var results = await drv.WriteAsync(
            [new WriteRequest("Coil", (sbyte)42)], CancellationToken.None);

        results.Single().StatusCode.ShouldBe(FocasStatusMapper.Good);
        var log = factory.Clients[0].PmcRangeWriteLog;
        log.Count.ShouldBe(1);
        log[0].Letter.ShouldBe("R");
        log[0].StartByte.ShouldBe(100);
        log[0].Bytes.ShouldBe(new byte[] { 42 });
        // Generic WriteAsync path is untouched — PMC byte goes through the typed entry point.
        factory.Clients[0].WriteLog.ShouldBeEmpty();
    }

    [Fact]
    public async Task PMC_bit_write_set_RMW_preserves_zero_byte_writes_only_target_bit()
    {
        // Prior byte = 0b0000_0000; set bit 3 → write byte = 0b0000_1000.
        var drv = NewDriverWithSeededPmc(
            writes: new FocasWritesOptions { Enabled = true, AllowPmc = true },
            tags: [new FocasTagDefinition("G50_3", Host, "G50.3", FocasDataType.Bit, Writable: true)],
            letter: "G", pathId: 1,
            seed: PmcBuffer(byteAddr: 50, value: 0b0000_0000),
            out var factory);
        await drv.InitializeAsync("{}", CancellationToken.None);

        var results = await drv.WriteAsync(
            [new WriteRequest("G50_3", true)], CancellationToken.None);

        results.Single().StatusCode.ShouldBe(FocasStatusMapper.Good);
        var log = factory.Clients[0].PmcRangeWriteLog.Single();
        log.Letter.ShouldBe("G");
        log.StartByte.ShouldBe(50);
        log.Bytes.ShouldBe(new byte[] { 0b0000_1000 });
    }

    [Fact]
    public async Task PMC_bit_write_set_preserves_other_bits_already_set()
    {
        // Prior byte = 0b1111_0000; set bit 0 → write byte = 0b1111_0001.
        var drv = NewDriverWithSeededPmc(
            writes: new FocasWritesOptions { Enabled = true, AllowPmc = true },
            tags: [new FocasTagDefinition("R50_0", Host, "R50.0", FocasDataType.Bit, Writable: true)],
            letter: "R", pathId: 1,
            seed: PmcBuffer(byteAddr: 50, value: 0b1111_0000),
            out var factory);
        await drv.InitializeAsync("{}", CancellationToken.None);

        await drv.WriteAsync([new WriteRequest("R50_0", true)], CancellationToken.None);

        var log = factory.Clients[0].PmcRangeWriteLog.Single();
        log.Bytes.ShouldBe(new byte[] { 0b1111_0001 });
    }

    [Fact]
    public async Task PMC_bit_write_clear_preserves_other_bits()
    {
        // Prior byte = 0b1111_1111; clear bit 0 → write byte = 0b1111_1110.
        var drv = NewDriverWithSeededPmc(
            writes: new FocasWritesOptions { Enabled = true, AllowPmc = true },
            tags: [new FocasTagDefinition("R50_0", Host, "R50.0", FocasDataType.Bit, Writable: true)],
            letter: "R", pathId: 1,
            seed: PmcBuffer(byteAddr: 50, value: 0xFF),
            out var factory);
        await drv.InitializeAsync("{}", CancellationToken.None);

        await drv.WriteAsync([new WriteRequest("R50_0", false)], CancellationToken.None);

        var log = factory.Clients[0].PmcRangeWriteLog.Single();
        log.Bytes.ShouldBe(new byte[] { 0b1111_1110 });
    }

    [Fact]
    public async Task Multiple_consecutive_bit_writes_in_same_byte_serialise()
    {
        // Each bit write does its own RMW (Read range -> mask -> Write range). Eight
        // consecutive bit-set writes on R100 starting from 0 must compose to 0xFF.
        var tags = Enumerable.Range(0, 8)
            .Select(b => new FocasTagDefinition($"Bit{b}", Host, $"R100.{b}", FocasDataType.Bit, Writable: true))
            .ToArray();
        var drv = NewDriverWithSeededPmc(
            writes: new FocasWritesOptions { Enabled = true, AllowPmc = true },
            tags: tags,
            letter: "R", pathId: 1,
            seed: PmcBuffer(byteAddr: 100, value: 0),
            out var factory);
        await drv.InitializeAsync("{}", CancellationToken.None);

        for (var b = 0; b < 8; b++)
            await drv.WriteAsync([new WriteRequest($"Bit{b}", true)], CancellationToken.None);

        var fake = factory.Clients[0];
        // 8 RMW round-trips, each writing the cumulative byte back.
        fake.PmcRangeWriteLog.Count.ShouldBe(8);
        fake.PmcByteRanges[("R", 1)][100].ShouldBe((byte)0xFF);
        // Every write hit the same byte address 100.
        fake.PmcRangeWriteLog.ShouldAllBe(e => e.StartByte == 100 && e.Bytes.Length == 1);
    }

    [Fact]
    public void Tag_classification_PMC_writable_yields_Operate()
    {
        // Server-layer ACL key — PMC tags require WriteOperate group membership
        // (mirrors MACRO; PARAM is the higher-friction Configure tier).
        var tag = new FocasTagDefinition(
            "Coil", Host, "R100.3", FocasDataType.Bit, Writable: true);

        FocasDriver.ClassifyTag(tag).ShouldBe(SecurityClassification.Operate);
    }

    [Fact]
    public void Tag_classification_PMC_non_writable_yields_ViewOnly()
    {
        var tag = new FocasTagDefinition(
            "Coil", Host, "R100.3", FocasDataType.Bit, Writable: false);

        FocasDriver.ClassifyTag(tag).ShouldBe(SecurityClassification.ViewOnly);
    }

    [Fact]
    public void FocasWritesOptions_default_AllowPmc_is_false()
    {
        // Defense in depth: a fresh FocasWritesOptions has every granular kill
        // switch off. A config row that omits AllowPmc must NOT silently flip PMC
        // writes on.
        new FocasWritesOptions().AllowPmc.ShouldBeFalse();
        new FocasDriverOptions().Writes.AllowPmc.ShouldBeFalse();
    }

    [Fact]
    public void Dto_round_trip_preserves_AllowPmc()
    {
        // JSON config -> FocasDriverOptions; the Writes.AllowPmc flag must survive
        // the bootstrapper's deserialize step. Sentinel: a write at a configured
        // PMC tag should NOT short-circuit to BadNotWritable when AllowPmc=true is
        // set in the JSON (the unimplemented backend will surface BadCommunicationError
        // instead).
        const string jsonAllowed = """
        {
          "Backend": "unimplemented",
          "Devices": [{ "HostAddress": "focas://10.0.0.5:8193" }],
          "Tags": [{
            "Name": "P", "DeviceHostAddress": "focas://10.0.0.5:8193",
            "Address": "R100", "DataType": "Byte", "Writable": true
          }],
          "Writes": { "Enabled": true, "AllowPmc": true }
        }
        """;

        var drv = FocasDriverFactoryExtensions.CreateInstance("drv-1", jsonAllowed);
        drv.InitializeAsync("{}", CancellationToken.None).GetAwaiter().GetResult();

        var results = drv.WriteAsync(
            [new WriteRequest("P", (sbyte)1)], CancellationToken.None).GetAwaiter().GetResult();
        // Key assertion: NOT BadNotWritable — that proves the AllowPmc gate didn't short-circuit.
        results.Single().StatusCode.ShouldNotBe(FocasStatusMapper.BadNotWritable);
    }

    [Fact]
    public void Dto_default_omitted_AllowPmc_keeps_safer_default()
    {
        // A Writes section with just { Enabled: true } must NOT silently flip the
        // granular kill switch on. PMC writes should still get BadNotWritable.
        const string json = """
        {
          "Backend": "unimplemented",
          "Devices": [{ "HostAddress": "focas://10.0.0.5:8193" }],
          "Tags": [{
            "Name": "P", "DeviceHostAddress": "focas://10.0.0.5:8193",
            "Address": "R100", "DataType": "Byte", "Writable": true
          }],
          "Writes": { "Enabled": true }
        }
        """;

        var drv = FocasDriverFactoryExtensions.CreateInstance("drv-1", json);
        drv.InitializeAsync("{}", CancellationToken.None).GetAwaiter().GetResult();

        var results = drv.WriteAsync(
            [new WriteRequest("P", (sbyte)1)], CancellationToken.None).GetAwaiter().GetResult();
        results.Single().StatusCode.ShouldBe(FocasStatusMapper.BadNotWritable);
    }

    private static byte[] PmcBuffer(int byteAddr, byte value)
    {
        // Allocate enough buffer to hold the byteAddr index, fill the chosen byte.
        var buf = new byte[byteAddr + 1];
        buf[byteAddr] = value;
        return buf;
    }
}