// core/rng.js (Lane F) — THE only randomness source in GUTS. qa.sh greps for violators.
// mulberry32: tiny, fast, deterministic. Same seed => same sequence, forever.

export function mulberry32(seed) {
  let a = seed >>> 0;
  return function () {
    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;
  };
}

// Named sub-streams so lanes don't perturb each other's sequences:
// rng('world'), rng('enemies'), ... each is an independent deterministic stream.
export function createRng(seed) {
  const streams = new Map();
  function hash(str) {
    let h = 2166136261 >>> 0;
    for (let i = 0; i < str.length; i++) { h ^= str.charCodeAt(i); h = Math.imul(h, 16777619); }
    return h >>> 0;
  }
  const rng = (stream = 'main') => {
    if (!streams.has(stream)) streams.set(stream, mulberry32((seed ^ hash(stream)) >>> 0));
    return streams.get(stream);
  };
  rng.seed = seed;
  rng.float = (stream, min = 0, max = 1) => min + rng(stream)() * (max - min);
  rng.int = (stream, min, max) => Math.floor(rng.float(stream, min, max + 1));
  return rng;
}