using System.Diagnostics.Metrics;
using System.Linq;
using FluentAssertions;
using StellaOps.Findings.Ledger.Observability;
using Xunit;


using StellaOps.TestKit;
namespace StellaOps.Findings.Ledger.Tests;

public class LedgerMetricsTests
{
    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void ProjectionLagGauge_RecordsLatestPerTenant()
    {
        using var listener = CreateListener();
        var measurements = new List<(double Value, KeyValuePair<string, object?>[] Tags)>();

        listener.SetMeasurementEventCallback<double>((instrument, measurement, tags, state) =>
        {
            if (instrument.Name == "ledger_projection_lag_seconds")
            {
                measurements.Add((measurement, tags.ToArray()));
            }
        });

        LedgerMetrics.RecordProjectionLag(TimeSpan.FromSeconds(42), "tenant-a");

        listener.RecordObservableInstruments();

        var measurement = measurements.Should().ContainSingle().Subject;
        measurement.Value.Should().BeApproximately(42, precision: 0.001);
        measurement.Tags.ToDictionary(kvp => kvp.Key, kvp => kvp.Value)
            .Should().Contain(new KeyValuePair<string, object?>("tenant", "tenant-a"));
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void MerkleAnchorDuration_EmitsHistogramMeasurement()
    {
        using var listener = CreateListener();
        var measurements = new List<(double Value, KeyValuePair<string, object?>[] Tags)>();

        listener.SetMeasurementEventCallback<double>((instrument, measurement, tags, state) =>
        {
            if (instrument.Name == "ledger_merkle_anchor_duration_seconds")
            {
                measurements.Add((measurement, tags.ToArray()));
            }
        });

        LedgerMetrics.RecordMerkleAnchorDuration(TimeSpan.FromSeconds(1.5), "tenant-b", 10);

        var measurement = measurements.Should().ContainSingle().Subject;
        measurement.Value.Should().BeApproximately(1.5, precision: 0.001);
        measurement.Tags.ToDictionary(kvp => kvp.Key, kvp => kvp.Value)
            .Should().Contain(new KeyValuePair<string, object?>("tenant", "tenant-b"));
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void MerkleAnchorFailure_IncrementsCounter()
    {
        using var listener = CreateListener();
        var measurements = new List<(long Value, KeyValuePair<string, object?>[] Tags)>();

        listener.SetMeasurementEventCallback<long>((instrument, measurement, tags, state) =>
        {
            if (instrument.Name == "ledger_merkle_anchor_failures_total")
            {
                measurements.Add((measurement, tags.ToArray()));
            }
        });

        LedgerMetrics.RecordMerkleAnchorFailure("tenant-c", "persist_failure");

        var measurement = measurements.Should().ContainSingle().Subject;
        measurement.Value.Should().Be(1);
        var tags = measurement.Tags.ToDictionary(kvp => kvp.Key, kvp => kvp.Value);
        tags.Should().Contain(new KeyValuePair<string, object?>("tenant", "tenant-c"));
        tags.Should().Contain(new KeyValuePair<string, object?>("reason", "persist_failure"));
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void AttachmentFailure_IncrementsCounter()
    {
        using var listener = CreateListener();
        var measurements = new List<(long Value, KeyValuePair<string, object?>[] Tags)>();

        listener.SetMeasurementEventCallback<long>((instrument, measurement, tags, state) =>
        {
            if (instrument.Name == "ledger_attachments_encryption_failures_total")
            {
                measurements.Add((measurement, tags.ToArray()));
            }
        });

        LedgerMetrics.RecordAttachmentFailure("tenant-d", "encrypt");

        var measurement = measurements.Should().ContainSingle().Subject;
        measurement.Value.Should().Be(1);
        var tags = measurement.Tags.ToDictionary(kvp => kvp.Key, kvp => kvp.Value);
        tags.Should().Contain(new KeyValuePair<string, object?>("tenant", "tenant-d"));
        tags.Should().Contain(new KeyValuePair<string, object?>("stage", "encrypt"));
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void BacklogGauge_ReflectsOutstandingQueue()
    {
        using var listener = CreateListener();
        var measurements = new List<(long Value, KeyValuePair<string, object?>[] Tags)>();

        // Reset
        LedgerMetrics.DecrementBacklog("tenant-q");

        LedgerMetrics.IncrementBacklog("tenant-q");
        LedgerMetrics.IncrementBacklog("tenant-q");
        LedgerMetrics.DecrementBacklog("tenant-q");

        listener.SetMeasurementEventCallback<long>((instrument, measurement, tags, state) =>
        {
            if (instrument.Name == "ledger_ingest_backlog_events")
            {
                measurements.Add((measurement, tags.ToArray()));
            }
        });

        listener.RecordObservableInstruments();

        var measurement = measurements.Should().ContainSingle().Subject;
        measurement.Value.Should().Be(1);
        measurement.Tags.ToDictionary(kvp => kvp.Key, kvp => kvp.Value)
            .Should().Contain(new KeyValuePair<string, object?>("tenant", "tenant-q"));
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void ProjectionRebuildHistogram_RecordsScenarioTags()
    {
        using var listener = CreateListener();
        var measurements = new List<(double Value, KeyValuePair<string, object?>[] Tags)>();

        listener.SetMeasurementEventCallback<double>((instrument, measurement, tags, state) =>
        {
            if (instrument.Name == "ledger_projection_rebuild_seconds")
            {
                measurements.Add((measurement, tags.ToArray()));
            }
        });

        LedgerMetrics.RecordProjectionRebuild(TimeSpan.FromSeconds(3.2), "tenant-r", "replay");

        var measurement = measurements.Should().ContainSingle().Subject;
        measurement.Value.Should().BeApproximately(3.2, 0.001);
        var tags = measurement.Tags.ToDictionary(kvp => kvp.Key, kvp => kvp.Value);
        tags.Should().Contain(new KeyValuePair<string, object?>("tenant", "tenant-r"));
        tags.Should().Contain(new KeyValuePair<string, object?>("scenario", "replay"));
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void DbConnectionsGauge_TracksRoleCounts()
    {
        using var listener = CreateListener();
        var measurements = new List<(long Value, KeyValuePair<string, object?>[] Tags)>();

        // Reset
        LedgerMetrics.DecrementDbConnection("writer");

        LedgerMetrics.IncrementDbConnection("writer");

        listener.SetMeasurementEventCallback<long>((instrument, measurement, tags, state) =>
        {
            if (instrument.Name == "ledger_db_connections_active")
            {
                measurements.Add((measurement, tags.ToArray()));
            }
        });

        listener.RecordObservableInstruments();

        var measurement = measurements.Should().ContainSingle().Subject;
        measurement.Value.Should().Be(1);
        measurement.Tags.ToDictionary(kvp => kvp.Key, kvp => kvp.Value)
            .Should().Contain(new KeyValuePair<string, object?>("role", "writer"));

        LedgerMetrics.DecrementDbConnection("writer");
    }

    [Trait("Category", TestCategories.Unit)]
        [Fact]
    public void VersionInfoGauge_EmitsConstantOne()
    {
        using var listener = CreateListener();
        var measurements = new List<(long Value, KeyValuePair<string, object?>[] Tags)>();

        listener.SetMeasurementEventCallback<long>((instrument, measurement, tags, state) =>
        {
            if (instrument.Name == "ledger_app_version_info")
            {
                measurements.Add((measurement, tags.ToArray()));
            }
        });

        listener.RecordObservableInstruments();

        var measurement = measurements.Should().ContainSingle().Subject;
        measurement.Value.Should().Be(1);
        var tags = measurement.Tags.ToDictionary(kvp => kvp.Key, kvp => kvp.Value);
        tags.Should().ContainKey("version");
        tags.Should().ContainKey("git_sha");
    }

    private static MeterListener CreateListener()
    {
        var listener = new MeterListener
        {
            InstrumentPublished = (instrument, l) =>
            {
                if (instrument.Meter.Name == "StellaOps.Findings.Ledger")
                {
                    l.EnableMeasurementEvents(instrument);
                }
            }
        };

        listener.Start();
        return listener;
    }
}