gulpfile tasks for compiling styles

gulp.styles.js

const gulp             	 = require('gulp');
const sass             	 = require('gulp-sass');
const path             	 = require('path');
const gutil            	 = require("gulp-util");
// custom importer for scss files that resolve file names in 
// main app.scss manifest
const importer         	 = require('../scssImporter'); 
const postcss          	 = require('gulp-postcss');
const autoprefixer     	 = require('autoprefixer');
const cssnano          	 = require('cssnano');
const rev              	 = require('gulp-rev');
const exec             	 = require('child_process').execSync;
// gets an array of all clientnames
const clients            = require('./clients')(); 

/*********************************
**********************************
********  Styles Tasks  **********
**********************************
**********************************/

gulp.task('buildStyles', () => {
  // Builds minified app.css files for every client and
  // delivers them to our static directory for our app
  const promises = [];

  clients.forEach(client => {
    const promise = new Promise((resolve) => {
      buildClientStyles(client, resolve);
    });
    promises.push(promise);
  });
  return Promise.all(promises);
});

function buildClientStyles(client, resolve = () => {}) {
  // some postcss plugins (autoprefixer is highly recommended, even life changing)
  const postcssPlugins = [
    autoprefixer({ browsers: ['last 2 versions'] }),
    cssnano()
  ];
  return gulp.src(path.resolve(__dirname, '../../styles/app.scss'))
    .pipe(sass({ importer: importer.bind({client}, Array.prototype.slice.call(arguments)) }))
    .pipe(postcss(postcssPlugins)
    .pipe(gulp.dest(`../../static/css/${client}`))
    .on('end', () => {
	gutil.log(`[sass] built ${client}`);
	resolve();
});

gulp.task('revisionStyles', ['buildStyles'], () => {
  // styles build for production
  // will remove the app.css file for each client and
  // replace it with a hash revision filename
  const promises = [];
  clients.forEach(client => {
    const promise = new Promise((resolve, reject) => {
      const appScssPath = '../../static/css', client, 'app.css';
      gulp.src(appScssPath)
        .pipe(rev())
        .pipe(gulp.dest(`../../static/css/${client}`))
        .on('end', () => {
	  exec(`rm ${appScssPath}`);
          gutil.log(`[sass] revisioned ${client}`);
          resolve();
      });
    });
    promises.push(promise);
  });
	  
  return Promise.all(promises);
});

// development build task
gulp.task('buildStylesDev', ['setDevVariables', 'buildStyles']);