TailSamplingHistogramAlignedReservoir.cs

using System.Diagnostics;
using OpenTelemetry.Metrics;

namespace Exemplars;

public class TailSamplingHistogramAlignedReservoir(IReadOnlyList<double> explicitBounds)
    : FixedSizeExemplarReservoir(explicitBounds.Count + 1)
{
    private readonly bool[] _recorded = new bool[explicitBounds.Count + 1];

    public override void Offer(in ExemplarMeasurement<long> measurement)
    {
        Debug.Fail("TailSamplingHistogramAlignedReservoir shouldn't be used with long values");
    }

    public override void Offer(in ExemplarMeasurement<double> measurement)
    {
        var index = GetBucketIndex(measurement.Value);

        if (_recorded[index])
        {
            return;
        }
        
        UpdateExemplar(index, measurement);
        Activity.Current?.AddTag("is_exemplar", true);
        _recorded[index] = true;
    }

    protected override void OnCollected()
    {
        Array.Clear(_recorded);
    }

    private int GetBucketIndex(double value)
    {
        for (var i = 0; i < explicitBounds.Count; i++)
        {
            if (value <= explicitBounds[i])
            {
                return i;
            }
        }
        
        return explicitBounds.Count;
    }
}