worker.js

'use strict';

/* Load Environment Variables */
require("dotenv-safe").config({
    path: `./config/.env.${process.env.NODE_ENV || 'development'}`,
    sample: "./config/.env.requirements",
    silent: true
});

// Load dependencies
require("./lib/root-require")();
const cluster = require('cluster');
const JobQueue = rootRequire('lib/job-queue');
const Logger = rootRequire('lib/logger');
const shutdownTimeout = 10 * 1000;

if (cluster.worker) {
  Logger.info('Worker process #%d loaded', cluster.worker.id);
}

// Thread shutdown procedure
const shutdownProcedure = () => {
    
    Logger.info('Queue shutting down');
    
    JobQueue.shutdown(shutdownTimeout, (error) => {

        if (error) {
            Logger.error('Queue shutdown error: ', error);
            process.exit(1);
        }

        process.exit(0);
    });
};


// Process failure events
process.on('SIGTERM', shutdownProcedure);
process.on('SIGINT', shutdownProcedure);

/**
 * Worker Processors
 * =================
 * 
 * These modules export functions that are able to process
 * jobs that are delivered through the JobQueue. The functions
 * they export are invoked with parameters for job metadata, and
 * a completion callback. 
 * 
 * When a processor finishes processing a job, the callback must be invoked. If t
 * he processor encounters an error while processing, an Error object can be passed 
 * as the first argument to the callback. Passing an error will notify the JobQueue 
 * to either reschedule the job, or mark the job as failed.
 */

const MusicBrainz = rootRequire('manifests/musicbrainz/processors');
const SpotifyProcessor = rootRequire('manifests/spotify/processors');


/**
 * JobQueue Router
 * ===============
 * 
 * The JobQueue can ingest many types of jobs, each with a unique name.
 * When the JobQueue delivers a job to be processed, a process function is
 * invoked with the job metadata. To notify the JobQueue that a job can be 
 * processed, JobQueue.process(), must be invoked with the following parameters.
 * 
 * 1. {string} - The name of the job
 * 2. {number} - How many jobs of this type can be processed at once
 * 3. {function} - How the job will be processed
 */

// MusicBrainz Processors
// TODO: Select which processors are active through command line args or env vars
JobQueue.process('musicbrainz:track', 1, MusicBrainz.Track);
JobQueue.process('musicbrainz:artist', 1, MusicBrainz.Artist);
JobQueue.process('musicbrainz:release:id', 1, MusicBrainz.ReleaseById);
JobQueue.process('musicbrainz:release:name', 1, MusicBrainz.ReleaseByName);

// Spotify Processors
JobQueue.process('spotify:track', 1, SpotifyProcessor.Track);
JobQueue.process('spotify:artist', 1, SpotifyProcessor.Artist);
JobQueue.process('spotify:release', 1, SpotifyProcessor.Release);