const validate = require('./validate')

/**
 * Convert array of 16 byte values to UUID string format of the form:
 * XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX
 */
const byteToHex = [];

for (let i = 0; i < 256; ++i) {
  byteToHex.push((i + 0x100).toString(16).substr(1));
}

function stringify(arr, offset = 0) {
  // Note: Be careful editing this code!  It's been tuned for performance
  // and works in ways you may not expect. See https://github.com/uuidjs/uuid/pull/434
  const uuid = (
    byteToHex[arr[offset + 0]] +
    byteToHex[arr[offset + 1]] +
    byteToHex[arr[offset + 2]] +
    byteToHex[arr[offset + 3]] +
    '-' +
    byteToHex[arr[offset + 4]] +
    byteToHex[arr[offset + 5]] +
    '-' +
    byteToHex[arr[offset + 6]] +
    byteToHex[arr[offset + 7]] +
    '-' +
    byteToHex[arr[offset + 8]] +
    byteToHex[arr[offset + 9]] +
    '-' +
    byteToHex[arr[offset + 10]] +
    byteToHex[arr[offset + 11]] +
    byteToHex[arr[offset + 12]] +
    byteToHex[arr[offset + 13]] +
    byteToHex[arr[offset + 14]] +
    byteToHex[arr[offset + 15]]
  ).toLowerCase();

  // Consistency check for valid UUID.  If this throws, it's likely due to one
  // of the following:
  // - One or more input array values don't map to a hex octet (leading to
  // "undefined" in the uuid)
  // - Invalid input values for the RFC `version` or `variant` fields
  if (!validate(uuid)) {
    throw TypeError('Stringified UUID is invalid');
  }

  return uuid;
}

module.exports = stringify;