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

namespace ZB.MOM.WW.OtOpcUa.Driver.S7.Tests;

/// <summary>
///     R07:P1 — once a pass has marked the connection dead (a wire op blew its deadline on a frozen
///     peer), the rest of that pass must not go to the wire: each further op would pay the full
///     timeout under the gate, so a 20-span pass took ~100 s and the comms-loss watchdog's clock only
///     started after it. The remaining items are stamped <c>BadCommunicationError</c> without I/O.
///     Every assertion counts wire operations; nothing is timed.
/// </summary>
[Trait("Category", "Unit")]
public sealed class S7DeadHandleShortCircuitTests
{
    private const uint BadCommunicationError = 0x80050000u;

    private static S7DriverOptions Options(int maxGap, params S7TagDefinition[] tags) => new()
    {
        Host = "192.0.2.1",
        Timeout = TimeSpan.FromSeconds(5),
        Probe = new S7ProbeOptions { Enabled = false },
        SpanReadMaxGapBytes = maxGap,
        RawTags = S7RawTags.Entries(tags),
    };

    /// <summary>Five isolated words — far enough apart that each is its own span.</summary>
    private static S7TagDefinition[] FarApartWords() =>
        [.. Enumerable.Range(0, 5).Select(i => new S7TagDefinition($"W{i}", $"DB{i + 1}.DBW0", S7DataType.UInt16, Writable: true))];

    private static string[] Refs(int n) => [.. Enumerable.Range(0, n).Select(i => $"W{i}")];

    private static async Task<(S7Driver, ScriptedS7PlcFactory)> StartAsync(S7DriverOptions options)
    {
        var factory = new ScriptedS7PlcFactory();
        var drv = new S7Driver(options, "s7-dead-short-circuit", factory);
        await drv.InitializeAsync("{}", TestContext.Current.CancellationToken);
        return (drv, factory);
    }

    /// <summary>Per-tag path: the first timeout ends the pass's wire traffic.</summary>
    [Fact]
    public async Task Per_tag_pass_stops_issuing_wire_ops_once_the_handle_is_dead()
    {
        var ct = TestContext.Current.CancellationToken;
        var (drv, factory) = await StartAsync(Options(maxGap: -1, FarApartWords()));
        using var _ = drv;
        factory.Read = (_, _) => throw new TimeoutException("frozen peer");

        var before = factory.WireOps;
        var r = await drv.ReadAsync(Refs(5), ct);

        (factory.WireOps - before).ShouldBe(1, "only the op that discovered the dead handle may go to the wire");
        r.ShouldAllBe(s => s.StatusCode == BadCommunicationError);
        drv.GetHealth().State.ShouldBe(DriverState.Degraded);

        // Positive control: the next pass reopens and serves every tag.
        factory.Read = (_, _) => Task.FromResult<object?>((ushort)1);
        var recovered = await drv.ReadAsync(Refs(5), ct);
        recovered.ShouldAllBe(s => s.StatusCode == 0u);
        factory.Created.Count.ShouldBe(2);
    }

    /// <summary>Span path: arrays are block reads even alone, so five arrays are five spans.</summary>
    [Fact]
    public async Task Span_pass_stops_issuing_wire_ops_once_the_handle_is_dead()
    {
        var ct = TestContext.Current.CancellationToken;
        S7TagDefinition[] arrays =
            [.. Enumerable.Range(0, 5).Select(i => new S7TagDefinition($"W{i}", $"DB{i + 1}.DBW0", S7DataType.UInt16, Writable: false, ArrayCount: 2))];
        var (drv, factory) = await StartAsync(Options(maxGap: 16, arrays));
        using var _ = drv;
        factory.ReadBytes = (_, _, _, _, _) => throw new TimeoutException("frozen peer");

        var before = factory.WireOps;
        var r = await drv.ReadAsync(Refs(5), ct);

        (factory.WireOps - before).ShouldBe(1);
        r.ShouldAllBe(s => s.StatusCode == BadCommunicationError);
    }

    /// <summary>
    ///     Multi-var path: a chunk that dies on a transport loss used to fall back to one per-tag read
    ///     per member — each paying the timeout again. Now it marks the handle dead and the fallback is
    ///     short-circuited.
    /// </summary>
    [Fact]
    public async Task Multi_var_transport_loss_does_not_fall_back_to_per_tag_wire_reads()
    {
        var ct = TestContext.Current.CancellationToken;
        var (drv, factory) = await StartAsync(Options(maxGap: 0, FarApartWords()));
        using var _ = drv;
        factory.ReadMulti = (_, _) => throw new TimeoutException("frozen peer");
        factory.Read = (_, _) => throw new TimeoutException("frozen peer");

        var before = factory.WireOps;
        var r = await drv.ReadAsync(Refs(5), ct);

        (factory.WireOps - before).ShouldBe(1);
        r.ShouldAllBe(s => s.StatusCode == BadCommunicationError);
        drv.GetHealth().State.ShouldBe(DriverState.Degraded);
    }

    /// <summary>
    ///     Positive control for the classification: a multi-var REFUSAL (not a transport loss) still
    ///     falls back per tag, so the members the CPU will serve are served.
    /// </summary>
    [Fact]
    public async Task Multi_var_refusal_still_falls_back_per_tag()
    {
        var ct = TestContext.Current.CancellationToken;
        var (drv, factory) = await StartAsync(Options(maxGap: 0, FarApartWords()));
        using var _ = drv;
        // The live snap7 shape of a multi-var with one refused item.
        factory.ReadMulti = (_, _) => throw new global::S7.Net.PlcException(global::S7.Net.ErrorCode.ReadData,
            new global::S7.Net.PlcException(global::S7.Net.ErrorCode.WrongNumberReceivedBytes));
        factory.Read = (_, _) => Task.FromResult<object?>((ushort)9);

        var before = factory.WireOps;
        var r = await drv.ReadAsync(Refs(5), ct);

        (factory.WireOps - before).ShouldBe(6, "one multi-var request, then one per-tag read each");
        r.ShouldAllBe(s => s.StatusCode == 0u);
        factory.Created.Count.ShouldBe(1, "a refusal is not a reason to reopen");
    }

    /// <summary>A refusal does not short-circuit the pass: the CPU answered, the handle is fine.</summary>
    [Fact]
    public async Task A_refusal_does_not_short_circuit_the_pass()
    {
        var ct = TestContext.Current.CancellationToken;
        var (drv, factory) = await StartAsync(Options(maxGap: -1, FarApartWords()));
        using var _ = drv;
        factory.Read = (addr, _) => addr == "DB1.DBW0"
            ? throw new Exception("Received error from PLC: Object does not exist.")
            : Task.FromResult<object?>((ushort)3);

        var before = factory.WireOps;
        var r = await drv.ReadAsync(Refs(5), ct);

        (factory.WireOps - before).ShouldBe(5);
        r.Skip(1).ShouldAllBe(s => s.StatusCode == 0u);
    }

    /// <summary>Write batch: the first transport loss fails the rest of the batch without I/O.</summary>
    [Fact]
    public async Task Write_batch_stops_issuing_wire_ops_once_the_handle_is_dead()
    {
        var ct = TestContext.Current.CancellationToken;
        var (drv, factory) = await StartAsync(Options(maxGap: -1, FarApartWords()));
        using var _ = drv;
        factory.Write = (_, _, _) => throw new System.IO.IOException("connection reset");

        var before = factory.WireOps;
        var w = await drv.WriteAsync([.. Refs(5).Select(r => new WriteRequest(r, (ushort)1))], ct);

        (factory.WireOps - before).ShouldBe(1);
        w.ShouldAllBe(x => x.StatusCode == BadCommunicationError);
        drv.GetHealth().State.ShouldBe(DriverState.Degraded);

        // Positive control: the next batch reopens and writes.
        factory.Write = (_, _, _) => Task.CompletedTask;
        (await drv.WriteAsync([.. Refs(5).Select(r => new WriteRequest(r, (ushort)1))], ct))
            .ShouldAllBe(x => x.StatusCode == 0u);
    }
}