using Microsoft.Extensions.Logging.Abstractions;

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

/// <summary>
/// Deferred-work register row 80 — <see cref="LocalDbReplicationStatusReporter"/> must
/// distinguish "replication is not configured on this node" (null, no reading) from
/// "replication is configured and the peer session is down" (false, a genuine fault).
/// </summary>
/// <remarks>
/// The replication engine is registered unconditionally on every site node and sits inert
/// without a peer, so <c>ISyncStatus</c> answers <c>Connected=false</c> / <c>OplogBacklog=0</c>
/// on a site that was never meant to replicate. Passing that straight through made rig
/// site-b/site-c publish "disconnected, empty backlog" — a healthy unreplicated site reading
/// as a broken replicated one, and central's null branches (conditional KPI emission,
/// sustained-badge anchor exclusion, per register row 33) never receiving the null they exist
/// for. The gate is supplied by the Host from <c>SiteLocalDbSetup.ReplicationIsConfigured</c>,
/// mirroring <c>SiteEventLogReplicationCheck</c>.
/// </remarks>
public class LocalDbReplicationStatusReporterTests
{
    private static LocalDbReplicationStatusReporter Build(
        SiteHealthCollector collector,
        bool replicationConfigured,
        bool connected = false,
        long? backlog = 0L) =>
        new(
            connectedProvider: () => connected,
            oplogBacklogProvider: () => backlog,
            replicationConfiguredProvider: () => replicationConfigured,
            collector: collector,
            logger: NullLogger<LocalDbReplicationStatusReporter>.Instance,
            refreshInterval: TimeSpan.FromHours(1));

    [Fact]
    public void Probe_ReplicationUnconfigured_PublishesNullForBothFields()
    {
        // The row-80 regression. The inert engine's false/0 must NOT reach the report.
        var collector = new SiteHealthCollector();
        using var reporter = Build(collector, replicationConfigured: false);

        reporter.Probe();
        var report = collector.CollectReport("TestSite");

        Assert.Null(report.LocalDbReplicationConnected);
        Assert.Null(report.LocalDbOplogBacklog);
    }

    [Fact]
    public void Probe_ReplicationUnconfigured_DoesNotReadTheSyncStatusProviders()
    {
        // The gate short-circuits rather than reading and discarding: an unconfigured node
        // should not be polling a replication engine it never uses. Also guards against a
        // future provider that throws when replication is off.
        var connectedReads = 0;
        var backlogReads = 0;
        var collector = new SiteHealthCollector();
        using var reporter = new LocalDbReplicationStatusReporter(
            connectedProvider: () => { connectedReads++; return false; },
            oplogBacklogProvider: () => { backlogReads++; return 0L; },
            replicationConfiguredProvider: () => false,
            collector: collector,
            logger: NullLogger<LocalDbReplicationStatusReporter>.Instance,
            refreshInterval: TimeSpan.FromHours(1));

        reporter.Probe();

        Assert.Equal(0, connectedReads);
        Assert.Equal(0, backlogReads);
    }

    [Fact]
    public void Probe_ReplicationConfiguredButDisconnected_PublishesFalse_NotNull()
    {
        // The other half of the contract, and the reason the fix is a gate rather than a
        // blanket "never report false": on a node that IS configured to replicate, a down
        // peer session is a real fault and must stay visible as false.
        var collector = new SiteHealthCollector();
        using var reporter = Build(
            collector, replicationConfigured: true, connected: false, backlog: 4200L);

        reporter.Probe();
        var report = collector.CollectReport("TestSite");

        Assert.False(report.LocalDbReplicationConnected);
        Assert.Equal(4200L, report.LocalDbOplogBacklog);
    }

    [Fact]
    public void Probe_ReplicationConfiguredAndConnected_PublishesTrue()
    {
        var collector = new SiteHealthCollector();
        using var reporter = Build(
            collector, replicationConfigured: true, connected: true, backlog: 0L);

        reporter.Probe();
        var report = collector.CollectReport("TestSite");

        Assert.True(report.LocalDbReplicationConnected);
        Assert.Equal(0L, report.LocalDbOplogBacklog);
    }

    [Fact]
    public void Probe_ReplicationConfigured_PreservesANullBacklogAsUnknown()
    {
        // A failed oplog poll on a REPLICATED node is "unknown", never 0 — rendering it as a
        // healthy empty backlog would report a pair that cannot read its own oplog as fine.
        // Connected stays false (the session really is down); only the backlog is unknown.
        var collector = new SiteHealthCollector();
        using var reporter = Build(
            collector, replicationConfigured: true, connected: false, backlog: null);

        reporter.Probe();
        var report = collector.CollectReport("TestSite");

        Assert.False(report.LocalDbReplicationConnected);
        Assert.Null(report.LocalDbOplogBacklog);
    }

    [Fact]
    public void Probe_ProviderThrows_LeavesThePreviousSnapshotIntact()
    {
        // Health reporting must never take the node down, and a failed probe must not
        // silently downgrade a good reading to null.
        var shouldThrow = false;
        var collector = new SiteHealthCollector();
        using var reporter = new LocalDbReplicationStatusReporter(
            connectedProvider: () => shouldThrow
                ? throw new InvalidOperationException("sync status unavailable")
                : true,
            oplogBacklogProvider: () => 7L,
            replicationConfiguredProvider: () => true,
            collector: collector,
            logger: NullLogger<LocalDbReplicationStatusReporter>.Instance,
            refreshInterval: TimeSpan.FromHours(1));

        reporter.Probe();
        shouldThrow = true;
        reporter.Probe();

        var report = collector.CollectReport("TestSite");
        Assert.True(report.LocalDbReplicationConnected);
        Assert.Equal(7L, report.LocalDbOplogBacklog);
    }

    [Fact]
    public void Probe_GateFlippedOn_StopsReportingNull()
    {
        // Turning replication on for a previously-unreplicated site is a both-nodes-together
        // restart in practice, but the gate is read per probe, so pin that it is not latched.
        var configured = false;
        var collector = new SiteHealthCollector();
        using var reporter = new LocalDbReplicationStatusReporter(
            connectedProvider: () => true,
            oplogBacklogProvider: () => 12L,
            replicationConfiguredProvider: () => configured,
            collector: collector,
            logger: NullLogger<LocalDbReplicationStatusReporter>.Instance,
            refreshInterval: TimeSpan.FromHours(1));

        reporter.Probe();
        Assert.Null(collector.CollectReport("TestSite").LocalDbReplicationConnected);

        configured = true;
        reporter.Probe();

        var report = collector.CollectReport("TestSite");
        Assert.True(report.LocalDbReplicationConnected);
        Assert.Equal(12L, report.LocalDbOplogBacklog);
    }

    [Fact]
    public void Constructor_NullReplicationConfiguredProvider_Throws()
    {
        Assert.Throws<ArgumentNullException>(() => new LocalDbReplicationStatusReporter(
            connectedProvider: () => false,
            oplogBacklogProvider: () => 0L,
            replicationConfiguredProvider: null!,
            collector: new SiteHealthCollector(),
            logger: NullLogger<LocalDbReplicationStatusReporter>.Instance));
    }
}