using Moq;
using Opc.Ua;
using Opc.Ua.Client;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;

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

/// <summary>
///     Regression coverage for the stale-session concurrency race in the alarm-acknowledge wire
///     path. A background reconnect handler can swap <see cref="OpcUaClientDriver.Session"/>
///     while a caller is parked on <c>_gate.WaitAsync</c>. If a method captures the session
///     reference <i>before</i> the gate and uses it afterwards, it issues the wire call against
///     the closed/stale session. The correct idiom — already used by ReadAsync/WriteAsync — is
///     a fast-fail guard outside the gate plus an authoritative re-read of <c>Session</c>
///     <i>inside</i> the gate. This test proves the acknowledge path follows it.
/// </summary>
/// <remarks>
///     The swap is staged so the race is exercised, not raced against:
///     <list type="number">
///         <item>The test acquires <c>_gate</c> first, so the method-under-test physically
///         cannot enter the critical section (read Session-in-gate / issue the wire call) until
///         the test releases the gate. Whatever the implementation does <i>after</i> the gate
///         therefore always sees the post-swap session.</item>
///         <item>The only thing that must be ordered is the <b>buggy</b> capture-before-gate:
///         its pre-gate NodeId parse reads the OLD session's <c>MessageContext</c>, which
///         completes a <see cref="TaskCompletionSource"/>. We wait on that signal so the swap
///         lands <i>after</i> the buggy capture has grabbed the OLD session — making the RED
///         outcome deterministic, not timing-dependent.</item>
///         <item>The fixed implementation reads no session member before the gate, so the
///         signal never fires; a bounded fallback then swaps+releases. That is correct for the
///         fixed path because its session read happens only after we release the gate, so the
///         swap is already visible regardless of ordering.</item>
///     </list>
///     A correct implementation re-reads <c>Session</c> inside the gate and lands the wire call
///     on the NEW session; the buggy capture-before-gate code lands it on the OLD one.
/// </remarks>
[Trait("Category", "Unit")]
public sealed class OpcUaClientStaleSessionRaceTests
{
    private static Mock<ISession> NewSessionMock(TaskCompletionSource? prologueReached = null)
    {
        var mock = new Mock<ISession>(MockBehavior.Loose);
        // NodeId parsing inside the driver resolves the reference against the session's
        // MessageContext. This getter is read in the driver's synchronous prologue (before the
        // gate), so signalling here proves the pre-gate capture path has run.
        mock.SetupGet(s => s.MessageContext)
            .Returns(new ServiceMessageContext(ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.SdkTelemetry.Context))
            .Callback(() => prologueReached?.TrySetResult());
        mock.SetupGet(s => s.NamespaceUris).Returns(new NamespaceTable());
        // Acknowledge issues its wire call via CallAsync; stub it so AcknowledgeAsync can run to
        // completion against whichever session it ends up binding to.
        mock.Setup(s => s.CallAsync(
                It.IsAny<RequestHeader>(),
                It.IsAny<CallMethodRequestCollection>(),
                It.IsAny<CancellationToken>()))
            .ReturnsAsync(new CallResponse
            {
                ResponseHeader = new ResponseHeader(),
                Results = new CallMethodResultCollection(),
                DiagnosticInfos = new DiagnosticInfoCollection(),
            });
        return mock;
    }

    private static void VerifyAckWireHitNewSessionNotOld(Mock<ISession> newSession, Mock<ISession> oldSession)
    {
        newSession.Verify(s => s.CallAsync(
            It.IsAny<RequestHeader>(), It.IsAny<CallMethodRequestCollection>(), It.IsAny<CancellationToken>()),
            Times.Once);
        oldSession.Verify(s => s.CallAsync(
            It.IsAny<RequestHeader>(), It.IsAny<CallMethodRequestCollection>(), It.IsAny<CancellationToken>()),
            Times.Never);
    }

    /// <summary>
    ///     AcknowledgeAsync issues its Acknowledge method <c>CallAsync</c> against the session
    ///     current after the gate — and parses the namespace-relative ConditionId against that
    ///     same session — rather than a reference captured before WaitAsync. This is the third
    ///     gate-protected wire site; the two subscribe paths (<c>SubscribeAsync</c>,
    ///     <c>SubscribeAlarmsAsync</c>) received the identical fix but are not covered here
    ///     because asserting them requires a live <c>Subscription</c> object (the SDK's
    ///     <c>AddSubscription</c>/<c>CreateAsync</c> can't be exercised through this mock seam);
    ///     their correctness is reviewable by inspection against this same idiom.
    /// </summary>
    [Fact]
    public async Task AcknowledgeAsync_uses_session_swapped_in_across_the_gate_not_the_captured_one()
    {
        var ct = TestContext.Current.CancellationToken;
        using var drv = new OpcUaClientDriver(new OpcUaClientDriverOptions(), "opcua-stale-ack");

        var prologueReached = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
        var oldSession = NewSessionMock(prologueReached);
        var newSession = NewSessionMock();
        drv.SetSessionForTest(oldSession.Object);

        await drv.Gate.WaitAsync(ct);

        var call = drv.AcknowledgeAsync(
            [new AlarmAcknowledgeRequest("ns=2;s=Pump17", "ns=2;s=Pump17", "operator ack")], ct);

        await WaitForPreGateCaptureOrFallbackAsync(prologueReached.Task, ct);
        drv.SetSessionForTest(newSession.Object);
        drv.Gate.Release();

        await call;

        VerifyAckWireHitNewSessionNotOld(newSession, oldSession);
    }

    /// <summary>
    ///     Awaits the buggy path's pre-gate-capture signal, or a bounded fallback when it never
    ///     fires (the fixed path performs no pre-gate session member read). The buggy-path signal
    ///     fires from a synchronous <c>MessageContext</c> read that runs before any await, so it
    ///     always wins the race well inside the fallback — keeping the RED outcome deterministic.
    ///     The fallback only matters for the GREEN (fixed) path where swap ordering is irrelevant
    ///     (the fixed read happens only after the gate is released), so a short bound keeps the
    ///     suite fast without weakening the guarantee.
    /// </summary>
    private static async Task WaitForPreGateCaptureOrFallbackAsync(Task signal, CancellationToken ct)
    {
        var fallback = Task.Delay(TimeSpan.FromMilliseconds(250), ct);
        await Task.WhenAny(signal, fallback);
    }
}