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

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

/// <summary>
///     Regression coverage for 05/STAB-4 — a per-tag libplctag runtime (a single <c>Tag</c>
///     handle) is cached in <c>DeviceState.Runtimes</c> and shared between the server read path,
///     every poll-group loop, and the alarm-projection loop. A <c>Tag</c> handle is not safe for
///     concurrent Read/GetStatus/Decode (or Encode/Write/GetStatus), so the driver must serialise
///     the whole sequence per runtime — mirrors <c>AbLegacyRuntimeConcurrencyTests</c>.
/// </summary>
[Trait("Category", "Unit")]
public sealed class AbCipRuntimeConcurrencyTests
{
    /// <summary>
    ///     A fake runtime that records the maximum number of operations in flight against the
    ///     <em>same</em> handle. If the driver fails to serialise, two callers overlap inside the
    ///     Read → GetStatus → Decode window and <see cref="MaxConcurrent"/> exceeds 1.
    /// </summary>
    private sealed class OverlapDetectingFake : FakeAbCipTag
    {
        private int _inFlight;

        /// <summary>Gets the maximum number of concurrent operations detected on this handle.</summary>
        public int MaxConcurrent { get; private set; }

        /// <summary>Initializes a new instance of the <see cref="OverlapDetectingFake"/> class.</summary>
        /// <param name="p">The tag creation parameters.</param>
        public OverlapDetectingFake(AbCipTagCreateParams p) : base(p) { }

        /// <inheritdoc />
        public override async Task ReadAsync(CancellationToken cancellationToken)
        {
            EnterOp();
            try
            {
                // Yield + small delay so an unserialised second caller is guaranteed to overlap.
                await Task.Delay(15, cancellationToken).ConfigureAwait(false);
                await base.ReadAsync(cancellationToken).ConfigureAwait(false);
            }
            finally { LeaveOp(); }
        }

        /// <inheritdoc />
        public override async Task WriteAsync(CancellationToken cancellationToken)
        {
            EnterOp();
            try
            {
                await Task.Delay(15, cancellationToken).ConfigureAwait(false);
                await base.WriteAsync(cancellationToken).ConfigureAwait(false);
            }
            finally { LeaveOp(); }
        }

        private void EnterOp()
        {
            var n = Interlocked.Increment(ref _inFlight);
            lock (this) { if (n > MaxConcurrent) MaxConcurrent = n; }
        }

        private void LeaveOp() => Interlocked.Decrement(ref _inFlight);
    }

    private static AbCipDriver NewDriver(FakeAbCipTagFactory factory, params AbCipTagDefinition[] tags)
    {
        var opts = new AbCipDriverOptions
        {
            Devices = [new AbCipDeviceOptions("ab://10.0.0.5/1,0")],
            Tags = tags,
        };
        return new AbCipDriver(opts, "drv-1", factory);
    }

    /// <summary>Verifies that concurrent reads of the same tag are serialised against the shared runtime.</summary>
    [Fact]
    public async Task Concurrent_reads_of_same_tag_are_serialised_against_the_shared_runtime()
    {
        OverlapDetectingFake? shared = null;
        var factory = new FakeAbCipTagFactory
        {
            Customise = p => shared = new OverlapDetectingFake(p) { Value = 7 },
        };
        var drv = NewDriver(factory,
            new AbCipTagDefinition("X", "ab://10.0.0.5/1,0", "Motor1.Speed", AbCipDataType.DInt));
        await drv.InitializeAsync("{}", CancellationToken.None);

        // Eight callers race for the same tag — mimics the server read path + poll loop(s) + the
        // alarm-projection loop hitting one cached runtime at once.
        var reads = Enumerable.Range(0, 8)
            .Select(_ => drv.ReadAsync(["X"], CancellationToken.None))
            .ToArray();
        await Task.WhenAll(reads);

        shared.ShouldNotBeNull();
        shared!.MaxConcurrent.ShouldBe(1, "operations on a shared libplctag Tag must not overlap");
        reads.ShouldAllBe(r => r.Result.Single().Value!.Equals(7));
    }

    /// <summary>Verifies that a concurrent read and write of the same tag do not overlap on the shared runtime.</summary>
    [Fact]
    public async Task Concurrent_read_and_write_of_same_tag_do_not_overlap()
    {
        OverlapDetectingFake? shared = null;
        var factory = new FakeAbCipTagFactory
        {
            Customise = p => shared = new OverlapDetectingFake(p) { Value = 1 },
        };
        var drv = NewDriver(factory,
            new AbCipTagDefinition("X", "ab://10.0.0.5/1,0", "Motor1.Speed", AbCipDataType.DInt));
        await drv.InitializeAsync("{}", CancellationToken.None);

        var readTask = drv.ReadAsync(["X"], CancellationToken.None);
        var writeTask = drv.WriteAsync([new WriteRequest("X", 99)], CancellationToken.None);
        await Task.WhenAll(readTask, writeTask);

        shared.ShouldNotBeNull();
        shared!.MaxConcurrent.ShouldBe(1);
    }
}