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

namespace ZB.MOM.WW.OtOpcUa.Core.Tests.Stability;

[Trait("Category", "Unit")]
public sealed class WedgeDetectorTests
{
    private static readonly DateTime Now = new(2026, 4, 19, 12, 0, 0, DateTimeKind.Utc);
    private static readonly TimeSpan Threshold = TimeSpan.FromSeconds(120);

    [Fact]
    public void SubSixtySecondThreshold_ClampsToSixty()
    {
        var detector = new WedgeDetector(TimeSpan.FromSeconds(10));
        detector.Threshold.ShouldBe(TimeSpan.FromSeconds(60));
    }

    [Fact]
    public void Unhealthy_Driver_AlwaysNotApplicable()
    {
        var detector = new WedgeDetector(Threshold);
        var demand = new DemandSignal(BulkheadDepth: 5, ActiveMonitoredItems: 10, QueuedHistoryReads: 0, LastProgressUtc: Now.AddMinutes(-10));

        detector.Classify(DriverState.Faulted, demand, Now).ShouldBe(WedgeVerdict.NotApplicable);
        detector.Classify(DriverState.Degraded, demand, Now).ShouldBe(WedgeVerdict.NotApplicable);
        detector.Classify(DriverState.Initializing, demand, Now).ShouldBe(WedgeVerdict.NotApplicable);
    }

    [Fact]
    public void Idle_Subscription_Only_StaysIdle()
    {
        // Idle driver: bulkhead 0, monitored items 0, no history reads queued.
        // Even if LastProgressUtc is ancient, the verdict is Idle, not Faulted.
        var detector = new WedgeDetector(Threshold);
        var demand = new DemandSignal(0, 0, 0, Now.AddHours(-12));

        detector.Classify(DriverState.Healthy, demand, Now).ShouldBe(WedgeVerdict.Idle);
    }

    [Fact]
    public void PendingWork_WithRecentProgress_StaysHealthy()
    {
        var detector = new WedgeDetector(Threshold);
        var demand = new DemandSignal(BulkheadDepth: 2, ActiveMonitoredItems: 0, QueuedHistoryReads: 0, LastProgressUtc: Now.AddSeconds(-30));

        detector.Classify(DriverState.Healthy, demand, Now).ShouldBe(WedgeVerdict.Healthy);
    }

    [Fact]
    public void PendingWork_WithStaleProgress_IsFaulted()
    {
        var detector = new WedgeDetector(Threshold);
        var demand = new DemandSignal(BulkheadDepth: 2, ActiveMonitoredItems: 0, QueuedHistoryReads: 0, LastProgressUtc: Now.AddMinutes(-5));

        detector.Classify(DriverState.Healthy, demand, Now).ShouldBe(WedgeVerdict.Faulted);
    }

    [Fact]
    public void MonitoredItems_Active_ButNoRecentPublish_IsFaulted()
    {
        // Subscription-only driver with live MonitoredItems but no publish progress within threshold
        // is a real wedge — this is the case the previous "no successful Read" formulation used
        // to miss (no reads ever happen).
        var detector = new WedgeDetector(Threshold);
        var demand = new DemandSignal(BulkheadDepth: 0, ActiveMonitoredItems: 5, QueuedHistoryReads: 0, LastProgressUtc: Now.AddMinutes(-10));

        detector.Classify(DriverState.Healthy, demand, Now).ShouldBe(WedgeVerdict.Faulted);
    }

    [Fact]
    public void MonitoredItems_Active_WithFreshPublish_StaysHealthy()
    {
        var detector = new WedgeDetector(Threshold);
        var demand = new DemandSignal(BulkheadDepth: 0, ActiveMonitoredItems: 5, QueuedHistoryReads: 0, LastProgressUtc: Now.AddSeconds(-10));

        detector.Classify(DriverState.Healthy, demand, Now).ShouldBe(WedgeVerdict.Healthy);
    }

    [Fact]
    public void HistoryBackfill_SlowButMakingProgress_StaysHealthy()
    {
        // Slow historian backfill — QueuedHistoryReads > 0 but progress advances within threshold.
        var detector = new WedgeDetector(Threshold);
        var demand = new DemandSignal(BulkheadDepth: 0, ActiveMonitoredItems: 0, QueuedHistoryReads: 50, LastProgressUtc: Now.AddSeconds(-60));

        detector.Classify(DriverState.Healthy, demand, Now).ShouldBe(WedgeVerdict.Healthy);
    }

    [Fact]
    public void WriteOnlyBurst_StaysIdle_WhenBulkheadEmpty()
    {
        // A write-only driver that just finished a burst: bulkhead drained, no subscriptions, no
        // history reads. Idle — the previous formulation would have faulted here because no
        // reads were succeeding even though the driver is perfectly healthy.
        var detector = new WedgeDetector(Threshold);
        var demand = new DemandSignal(0, 0, 0, Now.AddMinutes(-30));

        detector.Classify(DriverState.Healthy, demand, Now).ShouldBe(WedgeVerdict.Idle);
    }

    [Fact]
    public void DemandSignal_HasPendingWork_TrueForAnyNonZeroCounter()
    {
        new DemandSignal(1, 0, 0, Now).HasPendingWork.ShouldBeTrue();
        new DemandSignal(0, 1, 0, Now).HasPendingWork.ShouldBeTrue();
        new DemandSignal(0, 0, 1, Now).HasPendingWork.ShouldBeTrue();
        new DemandSignal(0, 0, 0, Now).HasPendingWork.ShouldBeFalse();
    }
}