// Seeded pseudo-random number generator (mulberry32)
export function createRng(seed: number) {
  let s = seed >>> 0;
  return () => {
    s += 0x6d2b79f5;
    let t = Math.imul(s ^ (s >>> 15), 1 | s);
    t ^= t + Math.imul(t ^ (t >>> 7), 61 | t);
    return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
  };
}

export function dateToSeed(date: string): number {
  // date = "YYYY-MM-DD"
  return date.split("-").reduce((acc, n) => acc * 1000 + parseInt(n), 0);
}

export function todayISO(): string {
  return new Date().toISOString().slice(0, 10);
}

export function shuffle<T>(arr: T[], rng: () => number): T[] {
  const a = [...arr];
  for (let i = a.length - 1; i > 0; i--) {
    const j = Math.floor(rng() * (i + 1));
    [a[i], a[j]] = [a[j], a[i]];
  }
  return a;
}