using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Driver.Ab.Transport.Cip;
using ZB.MOM.WW.OtOpcUa.Driver.Ab.Transport.Tests.Fakes;
namespace ZB.MOM.WW.OtOpcUa.Driver.Ab.Transport.Tests.Cip;

/// <summary>Press safety: <see cref="ForwardOpenThrottle"/> on fake time, and the storm it exists to stop.</summary>
[Collection(CipConnectionStatics.Name)]   // the storm test moves CipConnection's static counters
public sealed class ForwardOpenThrottleTests
{
    private static readonly TimeSpan Second = TimeSpan.FromSeconds(1);
    private static readonly TimeSpan Guard = TimeSpan.FromSeconds(10);
    private static CancellationToken TestCt => TestContext.Current.CancellationToken;

    [Fact]
    public async Task Second_attempt_inside_interval_waits()
    {
        var time = new ManualTimeProvider();
        var throttle = new ForwardOpenThrottle(Second, time);
        await throttle.RunAsync(_ => Task.FromResult(1), TestCt);
        time.Advance(TimeSpan.FromMilliseconds(400));

        var started = 0;
        var second = throttle.RunAsync(_ => { Interlocked.Increment(ref started); return Task.FromResult(2); }, TestCt);
        await time.WaitForTimerDueAtAsync(time.Start + Second, Guard);   // waits for the remainder, measured from attempt 1's start
        time.Advance(TimeSpan.FromMilliseconds(599));
        Volatile.Read(ref started).ShouldBe(0);
        second.IsCompleted.ShouldBeFalse();

        time.Advance(TimeSpan.FromMilliseconds(1));
        (await second.WaitAsync(Guard, TestCt)).ShouldBe(2);
        Volatile.Read(ref started).ShouldBe(1);
    }

    [Fact]
    public async Task Attempt_after_interval_proceeds_immediately()
    {
        var time = new ManualTimeProvider();
        var throttle = new ForwardOpenThrottle(Second, time);
        await throttle.RunAsync(_ => Task.FromResult(1), TestCt);
        time.Advance(Second);

        var started = false;
        var second = throttle.RunAsync(_ => { started = true; return Task.FromResult(2); }, TestCt);

        started.ShouldBeTrue();            // ran synchronously: no wait was needed
        second.IsCompletedSuccessfully.ShouldBeTrue();
        time.ArmedTimers.ShouldBe(0);
    }

    [Fact]
    public async Task Only_one_attempt_in_flight()
    {
        var time = new ManualTimeProvider();
        var throttle = new ForwardOpenThrottle(Second, time);
        var inFlight = 0;
        var maxInFlight = 0;
        var release = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);

        async Task<int> Attempt(CancellationToken _)
        {
            var now = Interlocked.Increment(ref inFlight);
            InterlockedMax(ref maxInFlight, now);
            await release.Task;
            Interlocked.Decrement(ref inFlight);
            return now;
        }

        var first = throttle.RunAsync(Attempt, TestCt);
        time.Advance(TimeSpan.FromSeconds(5));   // the interval is no obstacle; only the in-flight one is
        var others = Enumerable.Range(0, 4).Select(_ => throttle.RunAsync(Attempt, TestCt)).ToArray();
        // Positive control (#583): all four have reached the throttle and are parked behind the in-flight attempt.
        await FakeCipTarget.Until(() => throttle.Queued == 4, Guard, "four callers queued behind the first");
        Volatile.Read(ref inFlight).ShouldBe(1);
        others.ShouldAllBe(t => !t.IsCompleted);

        release.SetResult();
        await first.WaitAsync(Guard, TestCt);
        // Attempt 2 starts at once (attempt 1 started 5 s ago); each later one then waits out the
        // interval from its predecessor's start.
        await others[0].WaitAsync(Guard, TestCt);
        for (var i = 1; i < others.Length; i++)
        {
            await time.WaitForTimerDueAtAsync(time.GetUtcNow() + Second, Guard);
            time.Advance(Second);
            await FakeCipTarget.Until(() => others.Count(t => t.IsCompleted) == i + 1, Guard, $"attempt {i + 2}");
        }
        Volatile.Read(ref maxInFlight).ShouldBe(1);
    }

    [Fact]
    public async Task Caller_deadline_while_waiting_throws_throttled()
    {
        var time = new ManualTimeProvider();
        var throttle = new ForwardOpenThrottle(Second, time);
        await throttle.RunAsync(_ => Task.FromResult(1), TestCt);
        using var cts = new CancellationTokenSource();
        var invoked = false;

        var second = throttle.RunAsync(_ => { invoked = true; return Task.FromResult(2); }, cts.Token);
        await time.WaitForTimerDueAtAsync(time.Start + Second, Guard);
        await cts.CancelAsync();

        var ex = await Should.ThrowAsync<AbTransportException>(() => second.WaitAsync(Guard, TestCt));
        ex.Status.ShouldBe(AbStatus.BadConnection);
        ex.Message.ShouldContain("Forward Open throttled");
        invoked.ShouldBeFalse();
    }

    [Fact]
    public async Task A_wall_clock_step_does_not_shorten_the_interval()
    {
        var time = new ManualTimeProvider();
        var throttle = new ForwardOpenThrottle(Second, time);
        await throttle.RunAsync(_ => Task.FromResult(1), TestCt);

        time.WallClockOffset = TimeSpan.FromHours(1);   // NTP / DST / operator steps the clock forward
        var started = 0;
        var second = throttle.RunAsync(_ => { Interlocked.Increment(ref started); return Task.FromResult(2); }, TestCt);

        await time.WaitForTimerDueAtAsync(time.Start + Second, Guard);   // still parked for the full interval
        Volatile.Read(ref started).ShouldBe(0);
        time.Advance(Second);
        (await second.WaitAsync(Guard, TestCt)).ShouldBe(2);
    }

    [Fact]
    public async Task Refusing_target_sees_at_most_one_forward_open_per_interval()
    {
        // The storm: 50 callers hammering a device that refuses every Forward Open, for 3 s of fake time.
        // Attempt starts are >= 1 s apart, so t = 0, 1, 2, 3 is the most there can be.
        await using var target = new FakeCipTarget { ForwardOpenReply = FakeCipTarget.Refuse(0x01, 0x0113) };
        var time = new ManualTimeProvider();
        var options = new ConnectionOptions { ConnectionSize = 504, Timeout = TimeSpan.FromSeconds(2) };
        var throttle = new ForwardOpenThrottle(options.MinForwardOpenInterval, time);
        var conn = new CipConnection(new DeviceKey("127.0.0.1", target.Port, "1,0", "ControlLogix"), options, throttle, time);
        using var stop = CancellationTokenSource.CreateLinkedTokenSource(TestCt);
        var failures = 0;

        var callers = Enumerable.Range(0, 50).Select(_ => Task.Run(async () =>
        {
            while (!stop.IsCancellationRequested)
            {
                try { await conn.SendAsync(new byte[] { 0x4C, 0x00 }, stop.Token); }
                catch (AbTransportException) { Interlocked.Increment(ref failures); }
                catch (OperationCanceledException) { /* stopping */ }
            }
        }, TestCt)).ToArray();

        for (var step = 0; step < 30; step++)
        {
            await Task.Delay(10, TestCt);
            time.Advance(TimeSpan.FromMilliseconds(100));
        }
        // Positive control (#583), instead of a fixed settle: wait until the next attempt is parked on the interval.
        // Then no attempt is in flight and none can start until the clock moves, so every attempt the last step
        // released has already reached the wire and been counted.
        await FakeCipTarget.Until(() => throttle.IsWaitingOutInterval, Guard, "the next attempt to park on the interval");

        await stop.CancelAsync();
        await Task.WhenAll(callers).WaitAsync(Guard, TestCt);
        await conn.DisposeAsync();

        time.GetUtcNow().ShouldBe(time.Start + TimeSpan.FromSeconds(3));
        target.ForwardOpens.ShouldBeLessThanOrEqualTo(4);
        target.ForwardOpens.ShouldBeGreaterThanOrEqualTo(1);
        Volatile.Read(ref failures).ShouldBeGreaterThanOrEqualTo(target.ForwardOpens);
        target.ConnectedRequests.ShouldBe(0);
    }

    private static void InterlockedMax(ref int location, int value)
    {
        int current;
        while (value > (current = Volatile.Read(ref location)) &&
               Interlocked.CompareExchange(ref location, value, current) != current) { }
    }
}