var fs = require('fs'),
    glob = require('glob-fs')({ gitignore: true }),
    path = require('path'),
    mm = require('musicmetadata'),
    args = process.argv.slice(2),
    dir = args[0],
    outDir = args[1] || path.dirname(dir),
    files;

files = glob.readdirSync(dir);

files.forEach(function(file) {
  var parser = mm(fs.createReadStream(file), function (err, metadata) {
    if (err) throw err;
    var artist = metadata.artist.join(', ');
    var title = metadata.title;
    var newFilePath = path.join(outDir, (path.basename(file)).replace(path.basename(file, '.mp3'), `${artist} - ${title}`))

    fs.renameSync(file, newFilePath);
  });
});

// Usage
// node renameByMetadata.js path/to/directory/*.mp3 path/to/outDirectory(optional)
// Example: ReOrder, Driftmoon - #Slovakboys (Extended Mix), Driftmoon - #Slovakboys (Extended Mix).mp3