// -----------------------------------------------------------------------------
// ResolutionTelemetry.cs
// Sprint: SPRINT_1227_0001_0002_BE_resolution_api
// Task: T11 - Telemetry for resolution API
// -----------------------------------------------------------------------------


using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.DependencyInjection.Extensions;
using System.Diagnostics;
using System.Diagnostics.Metrics;

namespace StellaOps.BinaryIndex.WebService.Telemetry;

/// <summary>
/// OpenTelemetry instrumentation for binary resolution API.
/// </summary>
public sealed class ResolutionTelemetry : IDisposable
{
    public const string ServiceName = "StellaOps.BinaryIndex.Resolution";
    public const string MeterName = "StellaOps.BinaryIndex.Resolution";
    public const string ActivitySourceName = "StellaOps.BinaryIndex.Resolution";

    private readonly Meter _meter;

    // Counters
    private readonly Counter<long> _requestsTotal;
    private readonly Counter<long> _cacheHitsTotal;
    private readonly Counter<long> _cacheMissesTotal;
    private readonly Counter<long> _resolutionsTotal;
    private readonly Counter<long> _errorsTotal;
    private readonly Counter<long> _rateLimitedTotal;

    // Histograms
    private readonly Histogram<double> _requestDurationMs;
    private readonly Histogram<double> _cacheLatencyMs;
    private readonly Histogram<double> _fingerprintMatchDurationMs;
    private readonly Histogram<int> _batchSize;
    private readonly Histogram<double> _confidenceScore;

    // Gauges
    private readonly UpDownCounter<long> _requestsInProgress;

    public static readonly ActivitySource ActivitySource = new(ActivitySourceName);

    public ResolutionTelemetry(IMeterFactory? meterFactory = null)
    {
        _meter = meterFactory?.Create(MeterName) ?? new Meter(MeterName);

        _requestsTotal = _meter.CreateCounter<long>(
            "binaryindex.resolution.requests.total",
            unit: "{request}",
            description: "Total resolution API requests");

        _cacheHitsTotal = _meter.CreateCounter<long>(
            "binaryindex.resolution.cache.hits.total",
            unit: "{hit}",
            description: "Total cache hits");

        _cacheMissesTotal = _meter.CreateCounter<long>(
            "binaryindex.resolution.cache.misses.total",
            unit: "{miss}",
            description: "Total cache misses");

        _resolutionsTotal = _meter.CreateCounter<long>(
            "binaryindex.resolution.resolutions.total",
            unit: "{resolution}",
            description: "Total successful resolutions");

        _errorsTotal = _meter.CreateCounter<long>(
            "binaryindex.resolution.errors.total",
            unit: "{error}",
            description: "Total resolution errors");

        _rateLimitedTotal = _meter.CreateCounter<long>(
            "binaryindex.resolution.rate_limited.total",
            unit: "{request}",
            description: "Total rate-limited requests");

        _requestDurationMs = _meter.CreateHistogram<double>(
            "binaryindex.resolution.request.duration.ms",
            unit: "ms",
            description: "Request duration in milliseconds");

        _cacheLatencyMs = _meter.CreateHistogram<double>(
            "binaryindex.resolution.cache.latency.ms",
            unit: "ms",
            description: "Cache lookup latency in milliseconds");

        _fingerprintMatchDurationMs = _meter.CreateHistogram<double>(
            "binaryindex.resolution.fingerprint_match.duration.ms",
            unit: "ms",
            description: "Fingerprint matching duration in milliseconds");

        _batchSize = _meter.CreateHistogram<int>(
            "binaryindex.resolution.batch.size",
            unit: "{item}",
            description: "Batch request size");

        _confidenceScore = _meter.CreateHistogram<double>(
            "binaryindex.resolution.confidence",
            unit: "1",
            description: "Resolution confidence score distribution");

        _requestsInProgress = _meter.CreateUpDownCounter<long>(
            "binaryindex.resolution.requests.in_progress",
            unit: "{request}",
            description: "Requests currently in progress");
    }

    public void RecordRequest(string method, string status, TimeSpan duration, bool cacheHit)
    {
        var tags = new TagList
        {
            { ResolutionTelemetryTags.Method, method },
            { ResolutionTelemetryTags.Status, status },
            { ResolutionTelemetryTags.CacheHit, cacheHit.ToString().ToLowerInvariant() }
        };

        _requestsTotal.Add(1, tags);
        _requestDurationMs.Record(duration.TotalMilliseconds, tags);

        if (cacheHit)
            _cacheHitsTotal.Add(1, tags);
        else
            _cacheMissesTotal.Add(1, tags);
    }

    public void RecordResolution(string matchType, string resolutionStatus, decimal confidence)
    {
        var tags = new TagList
        {
            { ResolutionTelemetryTags.MatchType, matchType },
            { ResolutionTelemetryTags.ResolutionStatus, resolutionStatus }
        };

        _resolutionsTotal.Add(1, tags);
        _confidenceScore.Record((double)confidence, tags);
    }

    public void RecordError(string errorCode, string method)
    {
        _errorsTotal.Add(1, new TagList
        {
            { ResolutionTelemetryTags.ErrorCode, errorCode },
            { ResolutionTelemetryTags.Method, method }
        });
    }

    public void RecordRateLimited(string tenantId)
    {
        _rateLimitedTotal.Add(1, new TagList
        {
            { ResolutionTelemetryTags.TenantId, tenantId }
        });
    }

    public void RecordBatchRequest(int size)
    {
        _batchSize.Record(size);
    }

    public void RecordCacheLatency(TimeSpan latency, bool hit)
    {
        _cacheLatencyMs.Record(latency.TotalMilliseconds, new TagList
        {
            { ResolutionTelemetryTags.CacheHit, hit.ToString().ToLowerInvariant() }
        });
    }

    public void RecordFingerprintMatchDuration(TimeSpan duration, string algorithm)
    {
        _fingerprintMatchDurationMs.Record(duration.TotalMilliseconds, new TagList
        {
            { ResolutionTelemetryTags.Algorithm, algorithm }
        });
    }

    public void IncrementInProgress() => _requestsInProgress.Add(1);
    public void DecrementInProgress() => _requestsInProgress.Add(-1);

    public static Activity? StartResolveActivity(string package, string? cveId)
    {
        var activity = ActivitySource.StartActivity("Resolution.Resolve");
        activity?.SetTag("package", package);
        if (cveId != null) activity?.SetTag("cve_id", cveId);
        return activity;
    }

    public static Activity? StartBatchResolveActivity(int count)
    {
        var activity = ActivitySource.StartActivity("Resolution.ResolveBatch");
        activity?.SetTag("batch_size", count);
        return activity;
    }

    public void Dispose() => _meter.Dispose();
}

public static class ResolutionTelemetryTags
{
    public const string Method = "method";
    public const string Status = "status";
    public const string CacheHit = "cache_hit";
    public const string MatchType = "match_type";
    public const string ResolutionStatus = "resolution_status";
    public const string ErrorCode = "error_code";
    public const string TenantId = "tenant_id";
    public const string Algorithm = "algorithm";
}

public static class ResolutionTelemetryExtensions
{
    public static IServiceCollection AddResolutionTelemetry(this IServiceCollection services)
    {
        services.TryAddSingleton<ResolutionTelemetry>();
        return services;
    }
}