// format as hex number
export const hex = (n) => '0x' + n.toString(16);

// concatenate Uint8Array
export const concat = (a, b) => {
  const arr = new Uint8Array(a.length + b.length);
  arr.set(a);
  arr.set(b, a.length);
  return arr;
};

// like Array.reduce() but await each iteration
export const areduce = async (array, fn, state=null) => {
  for (const val of array) {
    state = await fn(val, state);
  }
  return state;
};

// generate array with range [a, b[ or [0, a[
export const range = (a, b=null) => {
  if (b === null) {
    b = a;
    a = 0;
  }

  const res = [];
  for (let i = a; i < b; i++)
    res.push(i);
  return res;
};

// return a Promise that resolves in n seconds
export const sleep = (n) => new Promise(res => setTimeout(res, n*1000));

// hash an ArrayBuffer
export const hash = (data, seed = 0) => {
  let h1 = 0xdeadbeef ^ seed;
  let h2 = 0x41c6ce57 ^ seed;

  data = new Uint8Array(data);
  for (const byte of data) {
    h1 = Math.imul(h1 ^ byte, 2654435761);
    h2 = Math.imul(h2 ^ byte, 1597334677);
  }

  h1 = Math.imul(h1 ^ (h1 >>> 16), 2246822507);
  h1 ^= Math.imul(h2 ^ (h2 >>> 13), 3266489909);
  h2 = Math.imul(h2 ^ (h2 >>> 16), 2246822507);
  h2 ^= Math.imul(h1 ^ (h1 >>> 13), 3266489909);
  return 4294967296 * (2097151 & h2) + (h1 >>> 0);
};