// Unbiased randomness from crypto.getRandomValues (available on http too).

const buf = new Uint32Array(1);

/** Uniform integer in [0, n). Rejection sampling avoids modulo bias. */
export function randomInt(n) {
  if (n <= 1) return 0;
  const limit = Math.floor(0x100000000 / n) * n;
  let x;
  do {
    crypto.getRandomValues(buf);
    x = buf[0];
  } while (x >= limit);
  return x % n;
}

/** Fisher–Yates shuffle, returns a new array. */
export function shuffle(arr) {
  const a = arr.slice();
  for (let i = a.length - 1; i > 0; i--) {
    const j = randomInt(i + 1);
    [a[i], a[j]] = [a[j], a[i]];
  }
  return a;
}

export function pick(arr) {
  return arr[randomInt(arr.length)];
}