step3/api/QuestionsApi/Services/ServiceMetrics.cs

using System.Text;

namespace QuestionsApi.Services;

public sealed class ServiceMetrics
{
    private long _attemptsCreated;
    private long _attemptDuplicates;
    private long _counterFailures;
    private long _ratingFailures;
    private long _reconciliations;
    private long _lastReconciliationUnixSeconds;
    private long _httpRequests;
    private long _httpDurationMicroseconds;
    private long _answerStatisticsBackfillComplete;
    private readonly System.Collections.Concurrent.ConcurrentDictionary<string, long> _dynamicSelections = new();
    private readonly System.Collections.Concurrent.ConcurrentDictionary<string, long> _dynamicAttempts = new();
    private readonly System.Collections.Concurrent.ConcurrentDictionary<string, long> _dynamicCorrect = new();
    private long _dynamicTargetGapTotal;

    public void AttemptCreated() => Interlocked.Increment(ref _attemptsCreated);
    public void AttemptDuplicate() => Interlocked.Increment(ref _attemptDuplicates);
    public void CounterFailure() => Interlocked.Increment(ref _counterFailures);
    public void RatingFailure() => Interlocked.Increment(ref _ratingFailures);
    public void AnswerStatisticsBackfillCompleted() => Interlocked.Exchange(ref _answerStatisticsBackfillComplete, 1);
    public void Reconciled()
    {
        Interlocked.Increment(ref _reconciliations);
        Interlocked.Exchange(ref _lastReconciliationUnixSeconds, DateTimeOffset.UtcNow.ToUnixTimeSeconds());
    }
    public void HttpRequest(TimeSpan duration)
    {
        Interlocked.Increment(ref _httpRequests);
        Interlocked.Add(ref _httpDurationMicroseconds, (long)(duration.TotalMilliseconds * 1000));
    }
    public void DynamicSelected(string tier, int targetGap)
    {
        _dynamicSelections.AddOrUpdate(tier, 1, (_, value) => value + 1);
        Interlocked.Add(ref _dynamicTargetGapTotal, Math.Abs(targetGap));
    }
    public void DynamicAttempt(string tier, bool correct)
    {
        _dynamicAttempts.AddOrUpdate(tier, 1, (_, value) => value + 1);
        if (correct) _dynamicCorrect.AddOrUpdate(tier, 1, (_, value) => value + 1);
    }

    public string RenderPrometheus()
    {
        var output = new StringBuilder();
        AppendCounter(output, "step3_question_attempts_created_total", Interlocked.Read(ref _attemptsCreated));
        AppendCounter(output, "step3_question_attempt_duplicates_total", Interlocked.Read(ref _attemptDuplicates));
        AppendCounter(output, "step3_answer_counter_failures_total", Interlocked.Read(ref _counterFailures));
        AppendCounter(output, "step3_rating_failures_total", Interlocked.Read(ref _ratingFailures));
        AppendCounter(output, "step3_answer_reconciliations_total", Interlocked.Read(ref _reconciliations));
        AppendCounter(output, "step3_http_requests_total", Interlocked.Read(ref _httpRequests));
        output.AppendLine("# TYPE step3_dynamic_selections_total counter");
        output.AppendLine("# TYPE step3_dynamic_attempts_total counter");
        output.AppendLine("# TYPE step3_dynamic_correct_total counter");
        foreach (var tier in _dynamicSelections.Keys.Order())
        {
            AppendLabeledSample(output, "step3_dynamic_selections_total", tier, _dynamicSelections.GetValueOrDefault(tier));
            AppendLabeledSample(output, "step3_dynamic_attempts_total", tier, _dynamicAttempts.GetValueOrDefault(tier));
            AppendLabeledSample(output, "step3_dynamic_correct_total", tier, _dynamicCorrect.GetValueOrDefault(tier));
        }
        AppendCounter(output, "step3_dynamic_target_gap_points_total", Interlocked.Read(ref _dynamicTargetGapTotal));
        output.AppendLine("# TYPE step3_http_request_duration_seconds summary");
        output.Append("step3_http_request_duration_seconds_count ")
            .Append(Interlocked.Read(ref _httpRequests))
            .AppendLine();
        output.Append("step3_http_request_duration_seconds_sum ")
            .Append((Interlocked.Read(ref _httpDurationMicroseconds) / 1_000_000.0).ToString("0.######", System.Globalization.CultureInfo.InvariantCulture))
            .AppendLine();
        output.AppendLine("# TYPE step3_answer_last_reconciliation_unixtime gauge");
        output.Append("step3_answer_last_reconciliation_unixtime ")
            .Append(Interlocked.Read(ref _lastReconciliationUnixSeconds))
            .AppendLine();
        output.AppendLine("# TYPE step3_answer_statistics_v2_backfill_complete gauge");
        output.Append("step3_answer_statistics_v2_backfill_complete ")
            .Append(Interlocked.Read(ref _answerStatisticsBackfillComplete))
            .AppendLine();
        return output.ToString();
    }

    private static void AppendCounter(StringBuilder output, string name, long value)
    {
        output.Append("# TYPE ").Append(name).AppendLine(" counter");
        output.Append(name).Append(' ').Append(value).AppendLine();
    }

    private static void AppendLabeledSample(StringBuilder output, string name, string tier, long value)
    {
        output.Append(name).Append("{tier=\"").Append(tier.Replace("\"", "")).Append("\"} ").Append(value).AppendLine();
    }
}