/**
 * @file random number generator
 * Based on https://stackoverflow.com/a/47593316/6003547
 */

let seeded: () => number = () => {
  throw new Error(
    "random generator was not seeded, please call `setSeed(str)`"
  );
};

export function setSeed(str: string) {
  const seed = xmur3(str);
  seeded = sfc32(seed(), seed(), seed(), seed());
  (seeded as any).seed = str;
}
export function random() {
  return seeded();
}

type NumberOfDice = 1 | 2 | 3;
type DiceSize = 4 | 6 | 8 | 10 | 12 | 20 | 100;
export type Dice = `${NumberOfDice}d${DiceSize}`;
export function roll(dice: Dice) {
  const [diceCount, diceSize] = dice.split("d").map(Number);
  let result = 0;
  for (let i = 0; i < diceCount; ++i) {
    result += Math.floor(random() * diceSize) + 1;
  }
  return result;
}

/**
 * Creates a seed function from string
 */
function xmur3(str: string) {
  let i: number, h: number;
  for (i = 0, h = 1779033703 ^ str.length; i < str.length; i++) {
    h = Math.imul(h ^ str.charCodeAt(i), 3432918353);
    h = (h << 13) | (h >>> 19);
  }
  return function () {
    h = Math.imul(h ^ (h >>> 16), 2246822507);
    h = Math.imul(h ^ (h >>> 13), 3266489909);
    return (h ^= h >>> 16) >>> 0;
  };
}

function sfc32(a: number, b: number, c: number, d: number) {
  return function () {
    a >>>= 0;
    b >>>= 0;
    c >>>= 0;
    d >>>= 0;
    let t = (a + b) | 0;
    a = b ^ (b >>> 9);
    b = (c + (c << 3)) | 0;
    c = (c << 21) | (c >>> 11);
    d = (d + 1) | 0;
    t = (t + d) | 0;
    c = (c + t) | 0;
    return (t >>> 0) / 4294967296;
  };
}