// mulberry32 PRNG. The generator state lives in state.rngState (a uint32) so a
// saved game resumes with the exact same sequence.

export function nextFloat(state) {
  state.rngState = (state.rngState + 0x6d2b79f5) >>> 0;
  let t = state.rngState;
  t = Math.imul(t ^ (t >>> 15), t | 1);
  t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
  return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
}

// Uniform in [-amp, amp].
export function nextNoise(state, amp) {
  return (nextFloat(state) * 2 - 1) * amp;
}

export function nextInt(state, maxExclusive) {
  return Math.floor(nextFloat(state) * maxExclusive);
}

export function pickWeighted(state, items, weights) {
  let total = 0;
  for (const w of weights) total += w;
  if (total <= 0) return null;
  let r = nextFloat(state) * total;
  for (let i = 0; i < items.length; i++) {
    r -= weights[i];
    if (r < 0) return items[i];
  }
  return items[items.length - 1];
}