/** pick up to random N elements from array.
 *  just shuffle it if N is unspecified or greater than the length of the array.
 *  the original array remains unmodified. */
export function sample<T>(arr: T[], n: number = arr.length): T[] {
  if (n > arr.length) return sample(arr, arr.length);
  const copy = [...arr];
  for (let i = 0; i < n; i++) {
    const j = i + Math.floor(Math.random() * (copy.length - i));
    [copy[i], copy[j]] = [copy[j] as T, copy[i] as T];
  }
  return copy.slice(0, n);
}

/** sleep for N milliseconds */
export const sleep = (msec: number) =>
  new Promise((resolve) => setTimeout(resolve, msec));