using Microsoft.Extensions.Logging.Abstractions;
using Microsoft.Extensions.Options;
using ZB.MOM.WW.ScadaBridge.Commons.Messages.Health;
using ZB.MOM.WW.ScadaBridge.Commons.Types.Enums;

namespace ZB.MOM.WW.ScadaBridge.HealthMonitoring.Tests;

/// <summary>
/// Register row 33: the sustained-backlog anchor behind the Health dashboard's
/// "Replication backlog" badge.
/// </summary>
/// <remarks>
/// The design constraint these tests exist to pin: a bare "backlog &gt; threshold" badge is
/// unusable, because the daily `site_events` retention purge is CDC-captured like any other
/// write and jumps the backlog by the deleted batch size before it drains. That spike is
/// expected and documented. So the aggregator holds the instant the backlog FIRST rose above
/// the threshold, and the badge only appears once the configured dwell has elapsed — healthy
/// means the backlog comes back down, which no point-in-time check can express.
/// </remarks>
public sealed class LocalDbBacklogSustainedTests
{
    private const long Threshold = 1000;

    [Fact]
    public void BacklogAboveThreshold_StartsTheClock()
    {
        var (aggregator, time) = NewAggregator();
        var start = time.GetUtcNow();

        aggregator.ProcessReport(Report("site-a", 1, backlog: Threshold + 1));

        Assert.Equal(start, aggregator.GetSiteState("site-a")!.LocalDbBacklogAboveSince);
    }

    [Fact]
    public void BacklogStayingAbove_KeepsTheOriginalStartInstant()
    {
        // The window must be sustained, not sliding: if each above-threshold report reset the
        // anchor, the dwell would never elapse and the badge could never appear at all.
        var (aggregator, time) = NewAggregator();
        var start = time.GetUtcNow();

        aggregator.ProcessReport(Report("site-a", 1, backlog: Threshold + 1));
        time.Advance(TimeSpan.FromMinutes(10));
        aggregator.ProcessReport(Report("site-a", 2, backlog: Threshold + 5000));

        Assert.Equal(start, aggregator.GetSiteState("site-a")!.LocalDbBacklogAboveSince);
    }

    [Fact]
    public void BacklogAtOrBelowThreshold_ClearsTheClock()
    {
        // The purge-burst exit path. A spike that drains must discard the anchor well before
        // the dwell elapses, so the expected daily burst never badges the site.
        var (aggregator, time) = NewAggregator();

        aggregator.ProcessReport(Report("site-a", 1, backlog: Threshold + 50_000));
        time.Advance(TimeSpan.FromMinutes(2));
        aggregator.ProcessReport(Report("site-a", 2, backlog: 0));

        Assert.Null(aggregator.GetSiteState("site-a")!.LocalDbBacklogAboveSince);
    }

    [Fact]
    public void BacklogExactlyAtThreshold_DoesNotStartTheClock()
    {
        // The comparison is strictly greater-than, so the threshold is the highest ACCEPTABLE
        // depth rather than the lowest alarming one.
        var (aggregator, _) = NewAggregator();

        aggregator.ProcessReport(Report("site-a", 1, backlog: Threshold));

        Assert.Null(aggregator.GetSiteState("site-a")!.LocalDbBacklogAboveSince);
    }

    [Fact]
    public void UnreplicatedSite_NeverAccumulatesAnAnchor()
    {
        // Rig site-b/site-c: a null backlog forever. Null means "no reading", never zero, so
        // it must never start a clock — otherwise every unreplicated site would eventually be
        // badged for a backlog it does not have.
        var (aggregator, time) = NewAggregator();

        aggregator.ProcessReport(Report("site-b", 1, backlog: null));
        time.Advance(TimeSpan.FromHours(6));
        aggregator.ProcessReport(Report("site-b", 2, backlog: null));

        Assert.Null(aggregator.GetSiteState("site-b")!.LocalDbBacklogAboveSince);
    }

    [Fact]
    public void NullBacklogMidClimb_LeavesTheAnchorUntouched()
    {
        // A failed poll on a replicated node reports null. That is not evidence the backlog
        // drained, so it must not clear the clock — a node that goes blind mid-climb would
        // otherwise silently reset its own dwell and never be badged.
        var (aggregator, time) = NewAggregator();
        var start = time.GetUtcNow();

        aggregator.ProcessReport(Report("site-a", 1, backlog: Threshold + 1));
        time.Advance(TimeSpan.FromMinutes(5));
        aggregator.ProcessReport(Report("site-a", 2, backlog: null));

        Assert.Equal(start, aggregator.GetSiteState("site-a")!.LocalDbBacklogAboveSince);
    }

    [Fact]
    public void FirstReportForANewSite_CanStartTheClock()
    {
        // The registration path is a separate branch from the update path; a site whose very
        // first report is already backlogged must not be missed.
        var (aggregator, time) = NewAggregator();
        var start = time.GetUtcNow();

        aggregator.ProcessReport(Report("brand-new", 1, backlog: Threshold + 1));

        Assert.Equal(start, aggregator.GetSiteState("brand-new")!.LocalDbBacklogAboveSince);
    }

    [Fact]
    public void ThresholdIsConfigurable()
    {
        var (aggregator, _) = NewAggregator(threshold: 10);

        aggregator.ProcessReport(Report("site-a", 1, backlog: 11));

        Assert.NotNull(aggregator.GetSiteState("site-a")!.LocalDbBacklogAboveSince);
    }

    [Fact]
    public void StaleReport_DoesNotDisturbTheAnchor()
    {
        // Out-of-order reports are rejected wholesale by the sequence-number guard; the anchor
        // must ride along with that rejection rather than being updated from stale data.
        var (aggregator, time) = NewAggregator();
        var start = time.GetUtcNow();

        aggregator.ProcessReport(Report("site-a", 5, backlog: Threshold + 1));
        time.Advance(TimeSpan.FromMinutes(5));
        aggregator.ProcessReport(Report("site-a", 2, backlog: 0));

        Assert.Equal(start, aggregator.GetSiteState("site-a")!.LocalDbBacklogAboveSince);
    }

    private static (CentralHealthAggregator Aggregator, TestTimeProvider Time) NewAggregator(
        long threshold = Threshold)
    {
        var time = new TestTimeProvider(DateTimeOffset.UtcNow);
        var opts = new HealthMonitoringOptions
        {
            OfflineTimeout = TimeSpan.FromSeconds(60),
            LocalDbBacklogThreshold = threshold,
        };
        var aggregator = new CentralHealthAggregator(
            Options.Create(opts), NullLogger<CentralHealthAggregator>.Instance, time);
        return (aggregator, time);
    }

    private static SiteHealthReport Report(string siteId, long seq, long? backlog) =>
        new(
            SiteId: siteId,
            SequenceNumber: seq,
            ReportTimestamp: DateTimeOffset.UtcNow,
            DataConnectionStatuses: new Dictionary<string, ConnectionHealth>(),
            TagResolutionCounts: new Dictionary<string, TagResolutionStatus>(),
            ScriptErrorCount: 0,
            AlarmEvaluationErrorCount: 0,
            StoreAndForwardBufferDepths: new Dictionary<string, int>(),
            DeadLetterCount: 0,
            DeployedInstanceCount: 0,
            EnabledInstanceCount: 0,
            DisabledInstanceCount: 0)
        {
            LocalDbOplogBacklog = backlog,
        };
}