ScadaBridge/tests/ZB.MOM.WW.ScadaBridge.HealthMonitoring.Tests/Kpi/CentralHealthAuditBacklogProviderTests.cs

using ZB.MOM.WW.ScadaBridge.Commons.Messages.Health;
using ZB.MOM.WW.ScadaBridge.Commons.Types;
using ZB.MOM.WW.ScadaBridge.Commons.Types.Enums;
using ZB.MOM.WW.ScadaBridge.HealthMonitoring.Kpi;

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

/// <summary>
/// Coverage for <see cref="CentralHealthAuditBacklogProvider"/>.
/// The provider sums the latest per-site <c>SiteAuditBacklog.PendingCount</c> across the
/// in-memory <see cref="ICentralHealthAggregator"/> — the same aggregate the live Audit
/// backlog tile shows — so the <c>backlogTotal</c> KPI history stops recording a hardwired
/// zero. Sites with no report or a null backlog snapshot contribute nothing.
/// </summary>
public class CentralHealthAuditBacklogProviderTests
{
    private static readonly DateTime At = new(2026, 6, 17, 12, 0, 0, DateTimeKind.Utc);

    /// <summary>Verifies that the pending backlog total sums the pending count across all sites.</summary>
    /// <returns>The result.</returns>
    [Fact]
    public void GetPendingBacklogTotal_Sums_PendingCount_Across_Sites()
    {
        var aggregator = new StubAggregator
        {
            States =
            {
                ["site-a"] = StateWithBacklog("site-a", 9),
                ["site-b"] = StateWithBacklog("site-b", 4),
                ["site-c"] = new SiteHealthState { SiteId = "site-c", LatestReport = null }, // heartbeat-only
            },
        };

        var provider = new CentralHealthAuditBacklogProvider(aggregator);

        // 9 + 4; the null-report site contributes nothing.
        Assert.Equal(13, provider.GetPendingBacklogTotal());
    }

    /// <summary>Verifies that the pending backlog total is zero when no site has reported a backlog.</summary>
    /// <returns>The result.</returns>
    [Fact]
    public void GetPendingBacklogTotal_Returns_Zero_When_No_Backlog_Reported()
    {
        var aggregator = new StubAggregator
        {
            States =
            {
                ["site-a"] = new SiteHealthState { SiteId = "site-a", LatestReport = MinimalReport("site-a") with { SiteAuditBacklog = null } },
                ["site-b"] = new SiteHealthState { SiteId = "site-b", LatestReport = null },
            },
        };

        var provider = new CentralHealthAuditBacklogProvider(aggregator);

        Assert.Equal(0, provider.GetPendingBacklogTotal());
    }

    private static SiteHealthState StateWithBacklog(string siteId, int pending) =>
        new()
        {
            SiteId = siteId,
            LatestReport = MinimalReport(siteId) with
            {
                SiteAuditBacklog = new SiteAuditBacklogSnapshot(
                    PendingCount: pending, OldestPendingUtc: null, OnDiskBytes: 0),
            },
        };

    private static SiteHealthReport MinimalReport(string siteId) =>
        new(
            SiteId: siteId,
            SequenceNumber: 1,
            ReportTimestamp: At,
            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);

    /// <summary>
    /// Hand-rolled <see cref="ICentralHealthAggregator"/> stub — the HealthMonitoring.Tests
    /// project has no mocking library. Only <see cref="GetAllSiteStates"/> is exercised.
    /// </summary>
    private sealed class StubAggregator : ICentralHealthAggregator
    {
        /// <summary>Gets the site health states served by the fake.</summary>
        public Dictionary<string, SiteHealthState> States { get; } = new();

        /// <inheritdoc />
        public IReadOnlyDictionary<string, SiteHealthState> GetAllSiteStates() => States;

        /// <inheritdoc />
        public SiteHealthState? GetSiteState(string siteId) =>
            States.TryGetValue(siteId, out var state) ? state : null;

        /// <inheritdoc />
        public void ProcessReport(SiteHealthReport report) => throw new NotSupportedException();

        /// <inheritdoc />
        public void MarkHeartbeat(string siteId, DateTimeOffset receivedAt) => throw new NotSupportedException();

        /// <inheritdoc />
        public void PruneUnknownSites(IReadOnlyCollection<string> knownSiteIds) => throw new NotSupportedException();
    }
}