/**
 * Shared randomness helpers.
 *
 * `Array.prototype.sort(() => 0.5 - Math.random())` is biased — modern V8
 * sorts use Timsort, which compares each element more than once and skews
 * the resulting permutation. Use `shuffle` for anything user-visible
 * (quiz options, review topic selection, leaderboards).
 */

export function shuffle(arr) {
  const out = [...arr];
  for (let i = out.length - 1; i > 0; i--) {
    const j = Math.floor(Math.random() * (i + 1));
    [out[i], out[j]] = [out[j], out[i]];
  }
  return out;
}

export function sample(arr, n) {
  if (n <= 0) return [];
  if (n >= arr.length) return shuffle(arr);
  return shuffle(arr).slice(0, n);
}

export function pickInt(min, maxInclusive) {
  const lo = Math.ceil(min);
  const hi = Math.floor(maxInclusive);
  return lo + Math.floor(Math.random() * (hi - lo + 1));
}