import { performance } from 'node:perf_hooks'

function percentile(sorted, p) {
  if (sorted.length === 0) return 0
  const idx = Math.min(sorted.length - 1, Math.floor(sorted.length * p))
  return sorted[idx]
}

export function getBenchOptions() {
  const runs = Number.parseInt(process.env.BENCH_RUNS ?? '8', 10)
  const warmup = Number.parseInt(process.env.BENCH_WARMUP ?? '2', 10)
  return {
    runs: Number.isFinite(runs) && runs > 1 ? runs : 8,
    warmup: Number.isFinite(warmup) && warmup >= 0 ? warmup : 2,
  }
}

export async function measure(name, fn, options) {
  const times = []

  for (let i = 0; i < options.runs; i++) {
    const t0 = performance.now()
    await fn()
    const dt = performance.now() - t0
    if (i >= options.warmup) {
      times.push(dt)
    }
  }

  times.sort((a, b) => a - b)
  const mean = times.reduce((sum, value) => sum + value, 0) / Math.max(1, times.length)

  return {
    name,
    samples: times.length,
    mean,
    min: times[0] ?? 0,
    p50: percentile(times, 0.5),
    p95: percentile(times, 0.95),
    max: times[times.length - 1] ?? 0,
  }
}

export function printResults(title, results, options) {
  console.log(`\n${title}`)
  console.log(`runs=${options.runs} warmup=${options.warmup} measured=${Math.max(0, options.runs - options.warmup)}`)
  for (const row of results) {
    console.log(
      `${row.name.padEnd(32)} n=${String(row.samples).padStart(2)} mean=${row.mean.toFixed(1)}ms ` +
      `p50=${row.p50.toFixed(1)}ms p95=${row.p95.toFixed(1)}ms min=${row.min.toFixed(1)}ms max=${row.max.toFixed(1)}ms`
    )
  }
}