utils/stats.ts

import type { Distribution } from '../types.js'

function quantile(sortedValues: number[], q: number): number {
  if (sortedValues.length === 0) return 0
  if (sortedValues.length === 1) return sortedValues[0]!
  const pos = (sortedValues.length - 1) * q
  const lower = Math.floor(pos)
  const upper = Math.ceil(pos)
  if (lower === upper) return sortedValues[lower]!
  const weight = pos - lower
  return sortedValues[lower]! * (1 - weight) + sortedValues[upper]! * weight
}

export function buildDistribution(values: number[]): Distribution | null {
  if (values.length === 0) return null
  const sorted = [...values].sort((a, b) => a - b)
  const total = sorted.reduce((sum, value) => sum + value, 0)
  return {
    min: sorted[0]!,
    max: sorted[sorted.length - 1]!,
    mean: total / sorted.length,
    p50: quantile(sorted, 0.5),
    p95: quantile(sorted, 0.95),
    p99: quantile(sorted, 0.99),
  }
}

export function clamp(value: number, min: number, max: number): number {
  return Math.min(max, Math.max(min, value))
}