/* eslint-disable no-mixed-operators */
/* eslint-disable no-bitwise */

// http://stackoverflow.com/questions/105034/how-to-create-a-guid-uuid-in-javascript/21963136#21963136
const lut: string[] = [];
for (let i = 0; i < 256; i++) {
  lut[i] = (i < 16 ? '0' : '') + i.toString(16);
}

export function generateUuid() {
  const d0 = (Math.random() * 0xffffffff) | 0;
  const d1 = (Math.random() * 0xffffffff) | 0;
  const d2 = (Math.random() * 0xffffffff) | 0;
  const d3 = (Math.random() * 0xffffffff) | 0;
  const uuid = `${
    lut[d0 & 0xff] +
    lut[(d0 >> 8) & 0xff] +
    lut[(d0 >> 16) & 0xff] +
    lut[(d0 >> 24) & 0xff]
  }-${lut[d1 & 0xff]}${lut[(d1 >> 8) & 0xff]}-${
    lut[((d1 >> 16) & 0x0f) | 0x40]
  }${lut[(d1 >> 24) & 0xff]}-${lut[(d2 & 0x3f) | 0x80]}${
    lut[(d2 >> 8) & 0xff]
  }-${lut[(d2 >> 16) & 0xff]}${lut[(d2 >> 24) & 0xff]}${lut[d3 & 0xff]}${
    lut[(d3 >> 8) & 0xff]
  }${lut[(d3 >> 16) & 0xff]}${lut[(d3 >> 24) & 0xff]}`;

  // .toUpperCase() here flattens concatenated strings to save heap memory space.
  return uuid.toUpperCase();
}