nodejs file copy

copy.js

var fs      = require('fs'),
    url     = require('url'),
    when    = require('when'),
    errors  = require('../errorHandling'),
    path    = require('path'),
    paths   = require('./paths'),

    appRoot = paths().appRoot,
    configExample = paths().configExample,
    configFile =  process.env.GHOST_CONFIG || paths().config,
    rejectMessage = 'Unable to load config';
    
function writeConfigFile() {
    var written = when.defer();

    /* Check for config file and copy from config.example.js
        if one doesn't exist. After that, start the server. */
    fs.exists(configExample, function checkTemplate(templateExists) {
        var read,
            write;

        if (!templateExists) {
            return errors.logError(new Error('Could not locate a configuration file.'), appRoot, 'Please check your deployment for config.js or config.example.js.');
        }

        // Copy config.example.js => config.js
        read = fs.createReadStream(configExample);
        read.on('error', function (err) {
            /*jslint unparam:true*/
            return errors.logError(new Error('Could not open config.example.js for read.'), appRoot, 'Please check your deployment for config.js or config.example.js.');
        });
        read.on('end', written.resolve);

        write = fs.createWriteStream(configFile);
        write.on('error', function (err) {
            /*jslint unparam:true*/
            return errors.logError(new Error('Could not open config.js for write.'), appRoot, 'Please check your deployment for config.js or config.example.js.');
        });

        read.pipe(write);
    });

    return written.promise;
}