using Akka.Actor;
using Akka.TestKit.Xunit2;
using ScadaLink.AuditLog.Central;

namespace ScadaLink.AuditLog.Tests.Central;

/// <summary>
/// Bundle E (M6-T7) tests for <see cref="SiteAuditTelemetryStalledTracker"/>.
/// The tracker subscribes to the actor system's EventStream for
/// <see cref="SiteAuditTelemetryStalledChanged"/> publications and maintains a
/// per-site latch the central health surface can read. Since reconciliation is
/// central-driven, the "stalled" state semantically belongs to central — not
/// to the per-site <see cref="ScadaLink.Commons.Messages.Health.SiteHealthReport"/>
/// payload (which the site itself emits). The tracker therefore lives as a
/// central singleton, not on the site health collector.
/// </summary>
public class SiteAuditTelemetryStalledTrackerTests : TestKit
{
    /// <summary>
    /// Helper: publishes a stalled-changed event on the actor system's
    /// EventStream and waits a moment for the tracker's subscribe callback to
    /// run. AwaitAssert avoids racing on the stream's async fan-out.
    /// </summary>
    private void PublishAndWait(SiteAuditTelemetryStalledTracker tracker, SiteAuditTelemetryStalledChanged evt)
    {
        Sys.EventStream.Publish(evt);
        AwaitAssert(
            () =>
            {
                var snapshot = tracker.Snapshot();
                Assert.True(snapshot.TryGetValue(evt.SiteId, out var stalled),
                    $"tracker did not record event for {evt.SiteId}");
                Assert.Equal(evt.Stalled, stalled);
            },
            duration: TimeSpan.FromSeconds(2),
            interval: TimeSpan.FromMilliseconds(20));
    }

    [Fact]
    public void Initial_Snapshot_IsEmpty()
    {
        using var tracker = new SiteAuditTelemetryStalledTracker(Sys);

        var snapshot = tracker.Snapshot();

        Assert.Empty(snapshot);
    }

    [Fact]
    public void StalledTrue_Event_TrackerReports_Stalled()
    {
        using var tracker = new SiteAuditTelemetryStalledTracker(Sys);

        PublishAndWait(tracker, new SiteAuditTelemetryStalledChanged("siteA", Stalled: true));

        var snapshot = tracker.Snapshot();
        Assert.True(snapshot["siteA"]);
    }

    [Fact]
    public void StalledFalse_Event_TrackerReports_NotStalled()
    {
        using var tracker = new SiteAuditTelemetryStalledTracker(Sys);

        // First flip the site into stalled so the false transition has a
        // prior value to overwrite — mirrors how the reconciliation actor
        // only publishes false after a true.
        PublishAndWait(tracker, new SiteAuditTelemetryStalledChanged("siteA", Stalled: true));
        PublishAndWait(tracker, new SiteAuditTelemetryStalledChanged("siteA", Stalled: false));

        var snapshot = tracker.Snapshot();
        Assert.False(snapshot["siteA"]);
    }

    [Fact]
    public void Multiple_Sites_Tracked_Independently()
    {
        using var tracker = new SiteAuditTelemetryStalledTracker(Sys);

        PublishAndWait(tracker, new SiteAuditTelemetryStalledChanged("siteA", Stalled: true));
        PublishAndWait(tracker, new SiteAuditTelemetryStalledChanged("siteB", Stalled: false));
        PublishAndWait(tracker, new SiteAuditTelemetryStalledChanged("siteC", Stalled: true));

        var snapshot = tracker.Snapshot();
        Assert.Equal(3, snapshot.Count);
        Assert.True(snapshot["siteA"]);
        Assert.False(snapshot["siteB"]);
        Assert.True(snapshot["siteC"]);
    }

    [Fact]
    public void Constructor_With_Null_ActorSystem_Throws()
    {
        Assert.Throws<ArgumentNullException>(
            () => new SiteAuditTelemetryStalledTracker((ActorSystem)null!));
    }

    [Fact]
    public void Dispose_Unsubscribes_From_EventStream()
    {
        var tracker = new SiteAuditTelemetryStalledTracker(Sys);

        PublishAndWait(tracker, new SiteAuditTelemetryStalledChanged("siteA", Stalled: true));

        tracker.Dispose();

        // After dispose any further events are ignored — the snapshot
        // reflects the last known state at dispose time.
        Sys.EventStream.Publish(new SiteAuditTelemetryStalledChanged("siteA", Stalled: false));

        // Give the stream a moment in case the unsubscribe is racey; the
        // assertion is that siteA stays at true.
        Thread.Sleep(50);
        Assert.True(tracker.Snapshot()["siteA"]);
    }
}