/**
 * シードデータ生成用の決定論的乱数ユーティリティ。
 * mulberry32 を用い、固定シードで再現可能なデータを生成する。
 */

export type Rng = () => number;

export function createRng(seed: number): Rng {
  let a = seed >>> 0;
  return () => {
    a |= 0;
    a = (a + 0x6d2b79f5) | 0;
    let t = Math.imul(a ^ (a >>> 15), 1 | a);
    t = (t + Math.imul(t ^ (t >>> 7), 61 | t)) ^ t;
    return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
  };
}

export function pick<T>(rng: Rng, arr: readonly T[]): T {
  return arr[Math.floor(rng() * arr.length)]!;
}

export function pickN<T>(rng: Rng, arr: readonly T[], n: number): T[] {
  return shuffle(rng, arr).slice(0, Math.min(n, arr.length));
}

export function randInt(rng: Rng, min: number, max: number): number {
  return Math.floor(rng() * (max - min + 1)) + min;
}

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

export function chance(rng: Rng, p: number): boolean {
  return rng() < p;
}

export function seededUuid(rng: Rng): string {
  const hex = () =>
    Math.floor(rng() * 0x10000)
      .toString(16)
      .padStart(4, '0');
  return `${hex()}${hex()}-${hex()}-${hex()}-${hex()}-${hex()}${hex()}${hex()}`;
}