gulpfile.js

const { watch, src, dest, series, parallel } =  require('gulp');
const less = require('gulp-less');
const clean = require('gulp-clean');
const path = require('path');


const cleanTask = () => {
  return src(
    [
      './assets/css/blog-enter.css',
      './assets/css/common.css',
      './assets/css/theme/*.css'
    ], {allowEmpty: true, read: false})
    .pipe(clean());
}

const lessTask = () => {
  return src(
    [
      './assets/less/blog-enter.less',
      './assets/less/common.less',
      './assets/less/theme/*.less'
    ])
    .pipe(less({
      paths: [ path.join(__dirname, 'less', 'includes') ]
    }))
    .pipe(dest((file) => {
      if (file.path.includes('theme')) {
        return './assets/css/theme/';
      }
      return './assets/css/';
    }));
}

const watchTask = () => {
  return watch(['./assets/**/*.less'], series(cleanTask, lessTask));  
}

exports.watch = watchTask;
exports.default = watchTask;