MoShiro/backend/src/MoShiro.Backend.Application/Query/Bucketing.cs

using MoShiro.Backend.Analysis;

namespace MoShiro.Backend.Application;

/// <summary>把源行合并成查询步长的桶：计数相加、直方图逐桶相加，所以结果是精确的，不是各点的平均。</summary>
public sealed class BucketedRows
{
    public BucketedRows(long[] t, MetricSet?[] sets, int[] rowCounts)
    {
        T = t;
        Sets = sets;
        RowCounts = rowCounts;
    }

    public long[] T { get; }

    public MetricSet?[] Sets { get; }

    /// <summary>每个桶合并了多少个源行（用来估算持续时长和覆盖率）。</summary>
    public int[] RowCounts { get; }

    public int TotalRows => RowCounts.Sum();

    public static BucketedRows Create(IReadOnlyList<SourceRow> rows, QueryRange range)
    {
        int n = range.Points;
        long[] t = new long[n];
        for (int i = 0; i < n; i++)
        {
            t[i] = range.FromMs + (i * range.StepMs);
        }

        var sets = new MetricSet?[n];
        int[] counts = new int[n];
        foreach (SourceRow row in rows)
        {
            long index = (row.Start - range.FromMs) / range.StepMs;
            if (row.Start < range.FromMs || index >= n)
            {
                continue;
            }

            int i = (int)index;
            if (sets[i] is null)
            {
                sets[i] = row.Set.Clone();
            }
            else
            {
                sets[i]!.Merge(row.Set);
            }

            counts[i]++;
        }

        return new BucketedRows(t, sets, counts);
    }

    /// <summary>整个时间段的精确合并。</summary>
    public MetricSet Merge()
    {
        var merged = new MetricSet();
        foreach (MetricSet? set in Sets)
        {
            if (set is not null)
            {
                merged.Merge(set);
            }
        }

        return merged;
    }
}