critical.js

const gulp = require('gulp')
const critical = require('critical')
const util = require('gulp-util')
// const rename = require('gulp-rename')
// const gulpif = require('gulp-if')
const htmlreplace = require('gulp-html-replace')
const path = require('path')

module.exports = {
    critialCss
}

gulp.task('critical', critialCss)

function critialCss() {
    const { paths, urlBase } = PATH_CONFIG.critical
		
		require('events').EventEmitter.defaultMaxListeners = 15
    util.log('starting critical css')

    return Promise.all(
        paths.map(({ url, source }) => {
            const options = {
                base: path.resolve(process.env.PWD, urlBase),
                src: path.resolve(process.env.PWD, url)
            }
            return new Promise((resolve, reject) => {
                critical
                    .generate({
                        ...options,
                        ...TASK_CONFIG.critical
                    })
                    .catch(e => {
                        console.error(e)
                        reject(e)
                    })
                    .then(output => {
                        gulp
                            .src(path.resolve(process.env.PWD, source))
                            .pipe(
                                htmlreplace(
                                    {
                                        critical: {
                                            src: null,
                                            tpl: `<style>${output}</style>`
                                        }
                                    },
                                    {
                                        keepBlockTags: true
                                    }
                                )
                            )
                            .pipe(
                                gulp.dest(
                                    path.resolve(
                                        process.env.PWD,
                                        source.split(source.substr(source.lastIndexOf('/')))[0]
                                    )
                                )
                            )
                            .on('end', resolve)
                    })
            }).catch(err => util.log(err))
        })
    )
}