Function createStatsStore

source code/context/stats.tsx:30–100

()

  max: number;
};
export function createStatsStore(): StatsStore {
  const metrics = new Map<string, number>();
  const histograms = new Map<string, Histogram>();
  const sets = new Map<string, Set<string>>();
  return {
    increment(name: string, value = 1) {
      metrics.set(name, (metrics.get(name) ?? 0) + value);
    },
    set(name: string, value: number) {
      metrics.set(name, value);
    },
    observe(name: string, value: number) {
      let h = histograms.get(name);
      if (!h) {
        h = {
          reservoir: [],
          count: 0,
          sum: 0,
          min: value,
          max: value
        };
        histograms.set(name, h);
      }
      h.count++;
      h.sum += value;
      if (value < h.min) {
        h.min = value;
      }
      if (value > h.max) {
        h.max = value;
      }
      // Reservoir sampling (Algorithm R)
      if (h.reservoir.length < RESERVOIR_SIZE) {
        h.reservoir.push(value);
      } else {
        const j = Math.floor(Math.random() * h.count);
        if (j < RESERVOIR_SIZE) {
          h.reservoir[j] = value;
        }
      }
    },
    add(name: string, value: string) {
      let s = sets.get(name);
      if (!s) {
        s = new Set();
        sets.set(name, s);
      }
      s.add(value);
    },
    getAll() {
      const result: Record<string, number> = Object.fromEntries(metrics);
      for (const [name, h] of histograms) {
        if (h.count === 0) {
          continue;
        }
        result[`${name}_count`] = h.count;
        result[`${name}_min`] = h.min;
        result[`${name}_max`] = h.max;