Gruntfile for fb-flo watcher, plus less+autoprefixer with watcher

gruntfile.js

/*
 * gruntfile based on https://gist.github.com/billyvg/2a7321623b2d2a87381c
 *
 * [grab the associated `package.json` from here](https://gist.github.com/robert-bosweb/6c0303c11839f063b854)
 * */

module.exports = function (grunt) {

    var pathToMainLessFile = "assets/less/"; // include the trailing forward slash
    var mainLessFileName = "central"; //.less is implied; leave it out
    
    var mainLessFile = pathToMainLessFile + mainLessFileName;

    // need to use var as key name; can it be done inside grunt.initConfig()?
    var lessMainFiles = {};
    lessMainFiles[mainLessFile + '.min.css'] = mainLessFile + '.less';

    grunt.initConfig({
        less: {
            main: {
                options: {
                    sourceMap: true,
                    compress: true,
                    sourceMapFilename: pathToMainLessFile + mainLessFileName + '.css.map',
                    sourceMapURL: mainLessFileName + '.css.map',
                    sourceMapRootpath: '/'
                },
                files: lessMainFiles
            }
        },
        autoprefixer: {
            options: {
                map: true
            },
            main: {
                src: mainLessFile + '.min.css',
                dest: mainLessFile + '.min.prefixed.css'
            }
        },
        watch:{
            lessFiles :{
                files: [
                    '**/*.less',
                    '!node_modules/**'
                ],
                tasks: ['lessPrefixed'],
                options: {}
            }
        },
        concurrent: {
            watchers: {
                tasks: ['flo', 'watch'],
                options: {
                    logConcurrentOutput: true
                }
            }
        }
    });

    grunt.loadNpmTasks('grunt-autoprefixer');
    grunt.loadNpmTasks('grunt-contrib-less');
    grunt.loadNpmTasks('grunt-contrib-watch');
    grunt.loadNpmTasks('grunt-concurrent');

    // configure your flo task
    grunt.registerTask('flo', 'Runs the fb-flo server for live editing', function () {
        var flo = require('fb-flo');
        var path = require('path');
        var fs = require('fs');
        //noinspection JSUnusedLocalSymbols
        var done = this.async();
        var WEBROOT = process.cwd();

        //noinspection JSUnusedLocalSymbols
        var server = flo(
            WEBROOT,
            {
                port:            8888,
                host:            'localhost',
                verbose:         false,
                persistent:      true,
                useFilePolling:  false,
                pollingInterval: 400,
                globs:           '**/*.css'
            },
            function (fp, callback) {
                var excludefile = !!( fp.match(/___$/) || fp.match(/^\.idea/) || fp.match(/\.git/) );
                if (!excludefile) {
                    console.log('fp: ' + fp);
                    callback({
                        resourceURL: '/' + fp,
                        contents:    fs.readFileSync(WEBROOT + '/' + fp).toString()
                        /*reload     : true*/
                    });
                }

                /*if (fp.match(/\.js$/)) {
                 callback({
                 resourceURL: fp.replace(/^web\/js/, '/js'),
                 contents   : fs.readFileSync(WEB_ROOT + '/' + fp).toString(),
                 reload: true
                 });
                 }
                 else if (fp.match(/^build.*?\.css$/)) {
                 callback({
                 resourceURL: fp.replace(/^build\/web\/css/, '/css'),
                 contents   : fs.readFileSync(WEB_ROOT + '/' + fp).toString(),
                 reload: true
                 });
                 }*/
            }
        );
    });

    grunt.registerTask('lessPrefixed', ['less:main', 'autoprefixer:main']);

    grunt.registerTask('default', ['lessPrefixed', 'concurrent:watchers']);
};