using System.Diagnostics;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Driver.Ab.Transport;
using ZB.MOM.WW.OtOpcUa.Driver.Ab.Transport.Tests.Fakes;

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

/// <summary>
///     Gitea #579: the native runtime's <c>Dispose</c> — which the driver calls under the tag's lock — used to
///     block for up to 2 s waiting for the last lease's Forward Close. It now releases in the background
///     (<see cref="ConnectionLease.ReleaseInBackground"/>, the same shape as the native AbLegacy runtime), and
///     these tests pin both halves of why that is safe: the caller is not held, and a re-create still cannot
///     overlap the close or leak a connection.
/// </summary>
[Trait("Category", "Unit")]
public sealed class NativeAbCipLeaseReleaseTests
{
    private static readonly TimeSpan Guard = TimeSpan.FromSeconds(15);
    private static CancellationToken Ct => TestContext.Current.CancellationToken;

    private static AbCipTagCreateParams Params(int port) => new(
        Gateway: "127.0.0.1",
        Port: port,
        CipPath: "1,0",
        LibplctagPlcAttribute: "controllogix",
        TagName: "T",
        Timeout: TimeSpan.FromSeconds(5),
        AllowPacking: false,
        ElementCount: 1,
        IsArray: false,
        AuthoredType: AbCipDataType.DInt,
        UseConnectedMessaging: true);

    /// <summary>A target whose Read Tag Fragmented (0x52) answers DINT 42.</summary>
    private static FakeCipTarget NewTarget()
    {
        var target = new FakeCipTarget();
        target.ConnectedHandler = req => Task.FromResult<byte[]?>(
            req[0] == 0x52 ? [0xD2, 0x00, 0x00, 0x00, 0xC4, 0x00, 0x2A, 0x00, 0x00, 0x00] : target.ServiceReply(req));
        return target;
    }

    [Fact]
    public async Task Release_under_the_tag_lock_returns_promptly_while_the_Forward_Close_is_still_pending()
    {
        await using var target = NewTarget();
        var closeHeld = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
        target.ForwardCloseGate = () => closeHeld.Task;
        var pool = new DeviceSessionPool();
        var factory = new NativeAbCipTagFactory(pool);

        var first = (NativeAbCipTagRuntime)factory.Create(Params(target.Port));
        await first.InitializeAsync(Ct);
        target.ForwardOpens.ShouldBe(1);

        // The driver disposes under the per-tag lock; hold one and time the release inside it.
        using var tagLock = new SemaphoreSlim(1, 1);
        await tagLock.WaitAsync(Ct);
        var sw = Stopwatch.StartNew();
        first.Dispose();
        sw.Stop();
        tagLock.Release();

        // The old Dispose waited up to 2 s for exactly this close; it must not wait at all now.
        sw.Elapsed.ShouldBeLessThan(TimeSpan.FromMilliseconds(500));
        await FakeCipTarget.Until(() => target.ForwardCloses == 1, Guard, "the Forward Close");
        (first.TeardownTask is null).ShouldBeFalse();
        first.TeardownTask!.IsCompleted.ShouldBeFalse(); // the close really is still pending

        // An immediate re-create (what the driver does after an evict) must NOT open a second session while
        // the first one's Forward Close is in flight (review finding 22) — the pool holds it behind the close.
        var second = (NativeAbCipTagRuntime)factory.Create(Params(target.Port));
        var init = second.InitializeAsync(Ct);
        // Positive control (#583): the second open has reached the pool's predecessor wait and parked there, so
        // the missing Forward Open below is that wait holding it — not the open simply not having got that far.
        await FakeCipTarget.Until(() => pool.Diagnostics.PredecessorWaits == 1, Guard, "the re-create to park behind the close");
        target.ForwardOpens.ShouldBe(1);
        init.IsCompleted.ShouldBeFalse();

        closeHeld.SetResult();
        await first.TeardownTask.WaitAsync(Guard, Ct);
        await init.WaitAsync(Guard, Ct);
        target.ForwardOpens.ShouldBe(2);
        second.GetStatus().ShouldBe((int)AbStatus.Ok);
        second.DecodeValue(AbCipDataType.DInt, null).ShouldBe(42);

        second.Dispose();
        await second.TeardownTask!.WaitAsync(Guard, Ct);
        target.ForwardCloses.ShouldBe(2);
    }

    /// <summary>
    ///     The offline soak: N create → read → release cycles, each release fire-and-forget and each create
    ///     immediately after it — the evict/re-create rhythm at its tightest. Every connection opened is closed
    ///     (one Forward Open and one Forward Close per cycle, one TCP connection per cycle), no TCP connection is
    ///     left open on the target, and the pool ends empty. A clock that runs fast lets the 1 s Forward Open
    ///     throttle (press safety) pass every cycle without the test taking N seconds; the throttle is still
    ///     exercised.
    /// </summary>
    [Fact]
    public async Task Repeated_create_and_release_cycles_leak_no_connection()
    {
        const int cycles = 25;
        await using var target = NewTarget();
        var pool = new DeviceSessionPool(new FastForwardClock());
        var factory = new NativeAbCipTagFactory(pool);

        NativeAbCipTagRuntime? last = null;
        for (var i = 0; i < cycles; i++)
        {
            var rt = (NativeAbCipTagRuntime)factory.Create(Params(target.Port));
            await rt.InitializeAsync(Ct).WaitAsync(Guard, Ct);
            rt.DecodeValue(AbCipDataType.DInt, null).ShouldBe(42);
            rt.Dispose(); // not awaited — the next cycle starts at once
            last = rt;
        }

        await last!.TeardownTask!.WaitAsync(Guard, Ct);
        await FakeCipTarget.Until(() => target.Server.OpenConnections == 0, Guard, "every TCP connection to close");
        target.ForwardOpens.ShouldBe(cycles);
        target.ForwardCloses.ShouldBe(cycles);
        target.Server.Connections.ShouldBe(cycles);
        pool.EntryCount.ShouldBe(0);
    }

    /// <summary>
    ///     Real timers, but a monotonic clock that jumps 10 s on every read — so an interval measured between
    ///     two reads has always "elapsed". The Forward Open throttle reads elapsed time this way; the only other
    ///     reader, the keep-alive idle check, runs on a real-time timer and at worst sends a harmless keep-alive.
    /// </summary>
    private sealed class FastForwardClock : TimeProvider
    {
        private long _skew;

        public override long GetTimestamp() =>
            System.GetTimestamp() + Interlocked.Add(ref _skew, 10 * System.TimestampFrequency);

        public override long TimestampFrequency => System.TimestampFrequency;
    }
}