var compileLess = require('broccoli-less-single');
var mergeTrees = require('broccoli-merge-trees');
...

module.exports = function(defaults) {

  var appTree = new Angular2App(defaults, {

    vendorNpmFiles: [

      'systemjs/dist/system-polyfills.js',

      'systemjs/dist/system.src.js',

      'zone.js/dist/**/*.+(js|js.map)',

      'es6-shim/es6-shim.js',

      'reflect-metadata/**/*.+(ts|js|js.map)',

      'rxjs/**/*.+(js|js.map)',

      '@angular/**/*.+(js|js.map)',

      'ng2-translate/**/*.+(js|js.map)',

      'ng2-bootstrap/**/*.+(js|js.map)',

      'codemirror/**/*.+(js|js.map)',

      'moment/moment.js',

      'font-awesome/**/*',

      'flag-icon-css/flags/**/*'

    ]

  });

  var less = mergeTrees(_.map(['common.less', 'app.less'], function(sassFile) {

    return compileLess([__dirname + '/less'], sassFile, sassFile.replace(/.less$/, '.css'), {

      paths: ['.', 'node_modules']

    });

  }));

  return mergeTrees([appTree, less], { overwrite: true });

};