/**
 * Tiny deterministic hash + PRNG for content preparation. Kept local because the engine (which has
 * its own seeded RNG) is not a dependency of @pintrush/db; content only needs a stable shuffle.
 */

/** 32-bit FNV-1a over the UTF-8 bytes of `text`. */
export function fnv1a(text: string): number {
  let hash = 0x811c9dc5;
  for (const byte of new TextEncoder().encode(text)) {
    hash ^= byte;
    hash = Math.imul(hash, 0x01000193) >>> 0;
  }
  return hash >>> 0;
}

/** mulberry32: small, fast, well-distributed 32-bit PRNG returning floats in [0, 1). */
export function mulberry32(seed: number): () => number {
  let a = seed >>> 0;
  return () => {
    a = (a + 0x6d2b79f5) >>> 0;
    let t = a;
    t = Math.imul(t ^ (t >>> 15), t | 1);
    t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
    return ((t ^ (t >>> 14)) >>> 0) / 4_294_967_296;
  };
}

/** Fisher–Yates shuffle of a copy of `items`, driven by a seed derived from `key`. */
export function seededShuffle<T>(items: readonly T[], key: string): T[] {
  const out = items.slice();
  const next = mulberry32(fnv1a(key));
  for (let i = out.length - 1; i > 0; i--) {
    const j = Math.floor(next() * (i + 1));
    const tmp = out[i] as T;
    out[i] = out[j] as T;
    out[j] = tmp;
  }
  return out;
}