using System.Diagnostics;
using System.Diagnostics.Metrics;
using FinalFactory.Rendezvous.Server.State;

namespace FinalFactory.Rendezvous.Server.Observability;

internal sealed class RendezvousTelemetry : IDisposable
{
    public const string MeterName = "FinalFactory.Rendezvous";
    public const string ActivitySourceName = "FinalFactory.Rendezvous.Server";

    private readonly InMemoryEphemeralRendezvousStore _store;
    private readonly Meter _meter = new(MeterName, "1.0.0");
    private readonly ActivitySource _activities = new(ActivitySourceName, "1.0.0");
    private readonly Counter<long> _httpRequests;
    private readonly Histogram<double> _httpDuration;
    private readonly Counter<long> _udpResults;
    private readonly Histogram<double> _udpDuration;
    private readonly Counter<long> _limiterDrops;
    private readonly Counter<long> _auditEvents;
    private readonly Counter<long> _connectionOutcomes;
    private readonly Counter<long> _operatorAuthentication;
    private readonly Histogram<double> _pairingLatency;

    public RendezvousTelemetry(InMemoryEphemeralRendezvousStore store)
    {
        _store = store;
        _httpRequests = _meter.CreateCounter<long>("rendezvous.http.requests");
        _httpDuration = _meter.CreateHistogram<double>(
            "rendezvous.http.duration",
            "ms");
        _udpResults = _meter.CreateCounter<long>("rendezvous.udp.results");
        _udpDuration = _meter.CreateHistogram<double>(
            "rendezvous.udp.duration",
            "ms");
        _limiterDrops = _meter.CreateCounter<long>("rendezvous.limiter.drops");
        _auditEvents = _meter.CreateCounter<long>("rendezvous.audit.events");
        _connectionOutcomes = _meter.CreateCounter<long>("rendezvous.connection.outcomes");
        _operatorAuthentication = _meter.CreateCounter<long>("rendezvous.operator.authentication");
        _pairingLatency = _meter.CreateHistogram<double>(
            "rendezvous.pairing.latency",
            "ms");
        _meter.CreateObservableGauge(
            "rendezvous.store.active_listings",
            () => _store.GetMetricsSnapshot().ActiveListings);
        _meter.CreateObservableGauge(
            "rendezvous.store.active_leases",
            () => _store.GetMetricsSnapshot().ActiveListings);
        _meter.CreateObservableGauge(
            "rendezvous.store.active_attempts",
            () => _store.GetMetricsSnapshot().ActiveJoinAttempts);
        _meter.CreateObservableGauge(
            "rendezvous.queue.depth",
            () => _store.GetMetricsSnapshot().ActiveJoinAttempts);
        _meter.CreateObservableGauge(
            "rendezvous.store.replay_markers",
            () => _store.GetMetricsSnapshot().ReplayMarkers);
        _meter.CreateObservableGauge(
            "rendezvous.store.available",
            () => _store.GetMetricsSnapshot().IsAvailable ? 1 : 0);
        _meter.CreateObservableCounter(
            "rendezvous.store.expiry_churn",
            () => _store.GetMetricsSnapshot().ExpiryChurn);
    }

    public Activity? StartActivity(string name, ActivityKind kind = ActivityKind.Internal) =>
        _activities.StartActivity(name, kind);

    public void RecordHttp(string operation, int statusCode, double elapsedMilliseconds)
    {
        TagList tags = new()
        {
            { "operation", operation },
            { "status_code", statusCode },
        };
        _httpRequests.Add(1, tags);
        _httpDuration.Record(elapsedMilliseconds, tags);
    }

    public void RecordUdp(string operation, string result, double elapsedMilliseconds)
    {
        TagList tags = new()
        {
            { "operation", operation },
            { "result", result },
        };
        _udpResults.Add(1, tags);
        _udpDuration.Record(elapsedMilliseconds, tags);
    }

    public void RecordLimiterDrop(string transport, string partition) =>
        _limiterDrops.Add(1, new TagList
        {
            { "transport", transport },
            { "partition", partition },
        });

    public void RecordAudit(string action, string result) =>
        _auditEvents.Add(1, new TagList
        {
            { "action", action },
            { "result", result },
        });

    public void RecordConnectionOutcome(string outcome, string elapsedBucket) =>
        _connectionOutcomes.Add(1, new TagList
        {
            { "outcome", outcome },
            { "elapsed_bucket", elapsedBucket },
        });

    public void RecordOperatorAuthentication(string result) =>
        _operatorAuthentication.Add(1, new TagList
        {
            { "result", result },
        });

    public void RecordPairingLatency(double elapsedMilliseconds) =>
        _pairingLatency.Record(elapsedMilliseconds);

    public void Dispose()
    {
        _activities.Dispose();
        _meter.Dispose();
    }
}