generateid.js

/**
 * @fileOverview Generate an Id
 */
const _ = require('lodash');
const {Hashids} = require('hashids');
const hashids = new Hashids(
    '',
    null,
    'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_-',
);

const NODE_ID_BITS = 10;
const SEQUENCE_BITS = 12;
const MAX_UINT32 = 0xFFFFFFFF;
const CUSTOM_EPOCH = 1514725199000;
const maxNodeID = Math.pow(2, NODE_ID_BITS) - 1;
const maxSequence = Math.pow(2, SEQUENCE_BITS) - 1;

let currentTimestamp = new Date().getTime() - CUSTOM_EPOCH;
let lastTimestamp = currentTimestamp;
let sequence = 0;

let nodeBuf;
const timeBuf = Buffer.alloc(8);

/**
 * Create a nodeId buffer
 *
 * Read in the mac addresses into a buffer
 *
 * @type {(function(): Buffer) & MemoizedFunction}
 */
const createNodeId = _.memoize(() => {
    nodeBuf = Buffer.alloc(2);
    const interfaces = require('os').networkInterfaces();
    const tmpNodeId = _.reduce(
        interfaces,
        (result, value, key) => {
            const mac = _.get(value, '0.mac').replace(/:/gm, '');
            // Remove lo
            if (mac === '000000000000') {
                return result;
            }

            result = Buffer.concat([
                result,
                Buffer.from(mac),
            ]);

            return result;
        },
        Buffer.alloc(NODE_ID_BITS),
    );

    let nodeId = tmpNodeId.readUInt32LE(0);
    nodeId = nodeId & maxNodeID;
    nodeBuf.writeUInt16LE(nodeId, 0);
});

/**
 * (-.-) zzZZ
 *
 * @return {Promise<undefined>}
 */
const sleep = () => {
    return new Promise((resolve) => setTimeout(resolve, 1000));
};

/**
 * Sets the time stamp to the time buffer
 *
 * @param {Number} currentTimestamp
 */
const addTimeStampToBuffer =(currentTimestamp) => {
    // split the 64 bit timestamp
    const big = ~~(currentTimestamp / MAX_UINT32);
    const low = (currentTimestamp % MAX_UINT32) - big;

    timeBuf.writeUInt32BE(big, 0);
    timeBuf.writeUInt32BE(low, 4);
};

addTimeStampToBuffer(currentTimestamp);
nodeBuf = createNodeId();

/**
 * Generates an id
 * @return {Promise<*>}
 */
module.exports = async () => {
    sequence = (currentTimestamp === lastTimestamp)
        ? (sequence + 1) & maxSequence
        : 0;

    // Sequence Exhausted, wait till next millisecond.
    if (sequence === 0) {
        await sleep();
        currentTimestamp = new Date().getTime() - CUSTOM_EPOCH;
        addTimeStampToBuffer(currentTimestamp)
    }

    lastTimestamp = currentTimestamp;

    const seqBuf = Buffer.alloc(2);
    seqBuf.writeUInt16BE(sequence);

    const idBuffer = Buffer.concat([seqBuf, nodeBuf, timeBuf]);
    return hashids.encodeHex(idBuffer.toString('hex'));
};