Batch watermark images with GM

watermark.js

var Q = require('q');
var async = require('async');
var fs = require('fs');
var gm = require('gm');
var join = require('path').join;
var readdir = Q.denodeify(fs.readdir);

var dir = join(__dirname, 'images');
var dest = join(__dirname, 'dest');
var logo = join(__dirname, 'resources/tlf-logo-medium.png');

/**
 *   Watermark image on bottom right
 */
function compositeWatermark(file) {
	var defered = Q.defer();

	if (/jpg|jpeg|png|gif|bmp/.test(file)) {
		gm(join(dir, file))
			.composite(logo)
			.gravity('South')
			.geometry('+0+100')
			.write(join(dest, file), function (err) {
				if (err) {
					console.log(err);
					defered.reject(err);
				} else {
					console.log('Complete Composite', file);
					defered.resolve();
				}
			});
	} else {
		console.log('Not an image', file);
		defered.resolve();
	}

	return defered.promise;
}

function openDir(path) {
    return readdir(path)
        .then(function(files) {
			async.eachSeries(files, function (file, callback) {
				compositeWatermark(file).then(callback);
			}, function (err) {
				if (err) throw err;
				console.log('Processing complete!');
				process.exit(1);
			});
		});
}

// proxy fs.exists to return a promise. Example of Q.defer
function exists(file){
    var deferred = Q.defer();
    fs.exists(file, function(result){
        return result ? deferred.resolve(file) : deferred.reject('invalid file');
    });
    return deferred.promise;
}

openDir(dir).done(function (err, data) {
	if (err) throw err;
});