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

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

/// <summary>
///     Review 2026-10-21 R06:T-1 — a pump the lifecycle abandoned (its teardown wait timed out) that finished after
///     the restart installed the NEW session published its stale cursor onto it: the old Agent's instanceId and
///     sequence replaced the new session's, so the next pump to start treated its first chunk as an Agent restart
///     (index cleared, a Bad flicker on every subscribed tag, a needless re-baseline). The pump now carries the
///     session generation it was started against and its cursor publish is dropped once that generation is gone.
/// </summary>
public sealed class MTConnectStaleCursorTests
{
    private const long InstanceB = 1655000099L;
    private const long NextSequenceB = 500L;
    private static readonly TimeSpan Watchdog = TimeSpan.FromSeconds(30);

    private static CancellationToken Ct => TestContext.Current.CancellationToken;

    /// <summary>The abandoned pump's late cursor publish leaves the new session's cursor alone.</summary>
    [Fact]
    public async Task An_abandoned_pump_does_not_publish_its_cursor_onto_the_new_session()
    {
        var clientA = CannedAgentClient.FromFixtures();
        var clientB = CannedAgentClient.FromFixtures();
        clientB.Current = new MTConnectStreamsResult(InstanceB, NextSequenceB, NextSequenceB - 10, clientB.Current.Observations);
        var clients = new Queue<CannedAgentClient>([clientA, clientB]);

        var driver = new MTConnectDriver(
            new MTConnectDriverOptions
            {
                AgentUri = "http://fixture-agent:5000",
                RequestTimeoutMs = 5000,
                Tags = [new MTConnectTagDefinition("dev1_pos", DriverDataType.Float64)],
            },
            "mt-t1",
            _ => clients.Dequeue());
        await driver.InitializeAsync("{}", Ct);

        var wedgeOnce = 0;
        var wedge = new ManualResetEventSlim(false);
        var entered = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
        driver.OnDataChange += (_, e) =>
        {
            if (e.Snapshot.Value is not 1.5d || Interlocked.Exchange(ref wedgeOnce, 1) != 0) return;
            entered.TrySetResult();
            wedge.Wait();
        };

        try
        {
            await driver.SubscribeAsync(["dev1_pos"], TimeSpan.FromMilliseconds(50), Ct);
            var pumpA = driver.SampleStreamTask.ShouldNotBeNull();
            _ = clientA.PumpAsync(MTConnectPumpGenerationChunks.Pos(108, 113, "1.5"));
            await entered.Task.WaitAsync(Watchdog, Ct);

            // The restart gives up on the wedged pump (bounded teardown wait), retires clientA and installs B.
            await driver.InitializeAsync("{}", Ct).WaitAsync(Watchdog, Ct);
            driver.AgentInstanceId.ShouldBe(InstanceB, "positive control: the new session is installed");
            pumpA.IsCompleted.ShouldBeFalse("pump A must still be alive — it is the late writer under test");

            // Now let the abandoned pump finish: its finally publishes (instanceA, 113).
            wedge.Set();
            await pumpA.WaitAsync(Watchdog, Ct);

            driver.AgentInstanceId.ShouldBe(InstanceB, "a superseded pump must not write the old Agent's instanceId");
            driver.AgentNextSequence.ShouldBe(NextSequenceB, "nor its cursor");
        }
        finally
        {
            wedge.Set();
            await driver.ShutdownAsync(CancellationToken.None);
        }
    }

    /// <summary>
    ///     Positive control: the CURRENT pump's own cursor publish still lands — a last unsubscribe stops it, and the
    ///     session's cursor moves to where that pump got to.
    /// </summary>
    [Fact]
    public async Task The_current_pump_still_publishes_its_cursor_when_it_stops()
    {
        var client = CannedAgentClient.FromFixtures();
        var driver = new MTConnectDriver(
            new MTConnectDriverOptions
            {
                AgentUri = "http://fixture-agent:5000",
                RequestTimeoutMs = 5000,
                Tags = [new MTConnectTagDefinition("dev1_pos", DriverDataType.Float64)],
            },
            "mt-t1-ok",
            _ => client);
        await driver.InitializeAsync("{}", Ct);
        try
        {
            var handle = await driver.SubscribeAsync(["dev1_pos"], TimeSpan.FromMilliseconds(50), Ct);
            await client.PumpAsync(MTConnectPumpGenerationChunks.Pos(108, 113, "1.5")).WaitAsync(Watchdog, Ct);

            await driver.UnsubscribeAsync(handle, Ct);

            driver.AgentNextSequence.ShouldBe(113);
        }
        finally
        {
            await driver.ShutdownAsync(CancellationToken.None);
        }
    }

    /// <summary>
    ///     Review I-1: a pump wedged inside its fan-out that comes back after the restart must not restore the NEW
    ///     session's health (nor mark its stream live for the read path) while the new pump's stream is down. Positive
    ///     control: the CURRENT pump's own chunk still restores Healthy.
    /// </summary>
    [Fact]
    public async Task An_abandoned_pump_does_not_restore_the_new_sessions_health()
    {
        var clientA = CannedAgentClient.FromFixtures();
        var clientB = CannedAgentClient.FromFixtures();
        clientB.SampleFailure = new IOException("connection refused");
        var clients = new Queue<CannedAgentClient>([clientA, clientB]);

        var driver = new MTConnectDriver(
            new MTConnectDriverOptions
            {
                AgentUri = "http://fixture-agent:5000",
                RequestTimeoutMs = 5000,
                Reconnect = new MTConnectReconnectOptions { MinBackoffMs = 50, MaxBackoffMs = 200 },
                Tags = [new MTConnectTagDefinition("dev1_pos", DriverDataType.Float64)],
            },
            "mt-i1",
            _ => clients.Dequeue());
        await driver.InitializeAsync("{}", Ct);

        var wedgeOnce = 0;
        var wedge = new ManualResetEventSlim(false);
        var entered = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
        driver.OnDataChange += (_, e) =>
        {
            if (e.Snapshot.Value is not 1.5d || Interlocked.Exchange(ref wedgeOnce, 1) != 0) return;
            entered.TrySetResult();
            wedge.Wait();
        };

        try
        {
            await driver.SubscribeAsync(["dev1_pos"], TimeSpan.FromMilliseconds(50), Ct);
            var pumpA = driver.SampleStreamTask.ShouldNotBeNull();
            _ = clientA.PumpAsync(MTConnectPumpGenerationChunks.Pos(108, 113, "1.5"));
            await entered.Task.WaitAsync(Watchdog, Ct);

            await driver.InitializeAsync("{}", Ct).WaitAsync(Watchdog, Ct);

            // The new session's pump fails its /sample: the driver goes Degraded.
            await clientB.WaitForSampleCallsAsync(1).WaitAsync(Watchdog, Ct);
            await WaitUntilAsync(() => driver.GetHealth().State == DriverState.Degraded, "the new stream is down");

            wedge.Set();
            await pumpA.WaitAsync(Watchdog, Ct);

            driver.GetHealth().State.ShouldBe(
                DriverState.Degraded, "a superseded pump must not report the new session's stream healthy");

            // Positive control: the new session's own stream recovering does restore Healthy.
            clientB.SampleFailure = null;
            var calls = clientB.SampleCallCount;
            await clientB.WaitForSampleCallsAsync(calls + 1).WaitAsync(Watchdog, Ct);
            await clientB.PumpAsync(MTConnectPumpGenerationChunks.Pos(108, 113, "2.5")).WaitAsync(Watchdog, Ct);
            driver.GetHealth().State.ShouldBe(DriverState.Healthy);
        }
        finally
        {
            wedge.Set();
            await driver.ShutdownAsync(CancellationToken.None);
        }
    }

    private static async Task WaitUntilAsync(Func<bool> condition, string because)
    {
        var deadline = DateTime.UtcNow + Watchdog;
        while (!condition() && DateTime.UtcNow < deadline) await Task.Delay(20, Ct);
        condition().ShouldBeTrue(because);
    }
}