'use strict';

const crypto = require('crypto');
const requireOptional = require('require_optional');

/**
 * Generate a UUIDv4
 */
const uuidV4 = () => {
  const result = crypto.randomBytes(16);
  result[6] = (result[6] & 0x0f) | 0x40;
  result[8] = (result[8] & 0x3f) | 0x80;
  return result;
};

/**
 * Returns the duration calculated from two high resolution timers in milliseconds
 *
 * @param {Object} started A high resolution timestamp created from `process.hrtime()`
 * @returns {Number} The duration in milliseconds
 */
const calculateDurationInMs = started => {
  const hrtime = process.hrtime(started);
  return (hrtime[0] * 1e9 + hrtime[1]) / 1e6;
};

/**
 * Relays events for a given listener and emitter
 *
 * @param {EventEmitter} listener the EventEmitter to listen to the events from
 * @param {EventEmitter} emitter the EventEmitter to relay the events to
 */
function relayEvents(listener, emitter, events) {
  events.forEach(eventName => listener.on(eventName, event => emitter.emit(eventName, event)));
}

// Grab Kerberos values if they exist, otherwise set them to null
let Kerberos = null;
let MongoAuthProcess = null;

try {
  const kerberos = requireOptional('kerberos');
  if (kerberos) {
    Kerberos = kerberos.Kerberos;
    MongoAuthProcess = kerberos.processes.MongoAuthProcess;
  }
} catch (err) {
  console.warn(err.message);
}

module.exports = {
  uuidV4,
  calculateDurationInMs,
  relayEvents,
  Kerberos,
  MongoAuthProcess
};