using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Commons.Messages.Drivers;
using ZB.MOM.WW.OtOpcUa.Runtime.Telemetry;

namespace ZB.MOM.WW.OtOpcUa.Runtime.Tests.Telemetry;

/// <summary>
///     Review 02 L4: <see cref="TelemetryLocalHub.Evict"/>'s tombstone set only ever shrank on a re-spawn of the
///     SAME id, so a driver removed for good kept its id forever. The tombstone is load-bearing (#609 — it holds
///     back the removed child's late writes), so it cannot simply be cleared; it is now timestamped and swept
///     once older than <see cref="TelemetryLocalHub.EvictionTombstoneTtl"/>, which outlives any in-flight
///     capability call by a wide margin.
/// </summary>
public sealed class TelemetryLocalHubTombstoneSweepTests
{
    private static DriverHealthChanged Health(string instanceId) =>
        new("cluster-a", instanceId, "Healthy", null, null, 0, DateTime.UtcNow);

    private static List<TelemetryItem> Drain(ITelemetrySubscription sub)
    {
        var items = new List<TelemetryItem>();
        while (sub.Reader.TryRead(out var item)) items.Add(item);
        return items;
    }

    [Fact]
    public void A_tombstone_holds_late_writes_until_the_ttl_then_is_swept()
    {
        var clock = new ManualTime { Now = new DateTimeOffset(2026, 10, 22, 12, 0, 0, TimeSpan.Zero) };
        var hub = new TelemetryLocalHub(clock);
        hub.Emit(new TelemetryItem.Health(Health("drv-a")));
        hub.Evict("drv-a");

        // Inside the TTL: the late write is dropped (the #609 contract) — and another eviction's sweep does
        // not lift a tombstone that is still young.
        clock.Now += TelemetryLocalHub.EvictionTombstoneTtl / 2;
        hub.Evict("drv-b");
        hub.Emit(new TelemetryItem.Health(Health("drv-a")));
        using (var sub = hub.Subscribe(16))
            Drain(sub).ShouldBeEmpty("a late write inside the TTL must still be held back");

        // Past the TTL: the next eviction sweeps drv-a's tombstone and its writes land again.
        clock.Now += TelemetryLocalHub.EvictionTombstoneTtl;
        hub.Evict("drv-c");
        hub.Emit(new TelemetryItem.Health(Health("drv-a")));
        using (var sub = hub.Subscribe(16))
            Drain(sub).OfType<TelemetryItem.Health>().Single().E.DriverInstanceId.ShouldBe("drv-a");
    }

    [Fact]
    public void Readmit_lifts_a_tombstone_before_its_ttl()
    {
        var clock = new ManualTime { Now = DateTimeOffset.UtcNow };
        var hub = new TelemetryLocalHub(clock);
        hub.Evict("drv-a");
        hub.Readmit("drv-a");

        hub.Emit(new TelemetryItem.Health(Health("drv-a")));
        using var sub = hub.Subscribe(16);
        Drain(sub).Count.ShouldBe(1);
    }

    private sealed class ManualTime : TimeProvider
    {
        public DateTimeOffset Now { get; set; }
        public override DateTimeOffset GetUtcNow() => Now;
    }
}