import type { Stat } from './types.ts';

// Nearest-rank percentile over a copy of the values.
function percentile(sorted: number[], p: number): number {
  if (sorted.length === 0) return Number.NaN;
  const rank = Math.ceil((p / 100) * sorted.length);
  const idx = Math.min(sorted.length - 1, Math.max(0, rank - 1));
  return sorted[idx];
}

export function summarize(values: number[]): Stat | null {
  const clean = values.filter((v) => Number.isFinite(v));
  if (clean.length === 0) return null;
  const sorted = [...clean].sort((a, b) => a - b);
  return {
    n: sorted.length,
    min: sorted[0],
    median: percentile(sorted, 50),
    p95: percentile(sorted, 95),
    max: sorted[sorted.length - 1],
  };
}