gulpfile.js

var gulp = require('gulp');
var browserSync = require('browser-sync');
var sass = require('gulp-sass');
var prefix = require('gulp-autoprefixer');
var cp = require('child_process');
var nano = require('gulp-cssnano');
var maps = require('gulp-sourcemaps');
var uglify = require('gulp-uglify');
var rename = require('gulp-rename');
var imagemin = require('gulp-imagemin');
var pngquant = require('imagemin-pngquant');
var purgecss = require('gulp-purgecss');

var jekyll = process.platform === 'win32' ? 'jekyll.bat' : 'jekyll';
var messages = {
  jekyllBuild: '<span style="color: grey">Running:</span> $ jekyll build'
};

/**
 * Build the Jekyll Site
 */
gulp.task('jekyll-build', function(done) {
  browserSync.notify(messages.jekyllBuild);
  return cp
    .spawn('bundle', ['exec', 'jekyll', 'build', '--config', '_config.yml'], {
      stdio: 'inherit'
    })
    .on('close', done);
});

gulp.task('jekyll-serve', function(done) {
  browserSync.notify(messages.jekyllBuild);
  return cp
    .spawn('bundle', ['exec', 'jekyll', 'serve'], {
      stdio: 'inherit'
    })
    .on('close', done);
});

/**
 * Rebuild Jekyll & do page reload
 */
gulp.task('jekyll-rebuild', gulp.series(['jekyll-build'], function() {
    browserSync.reload();
  })
);



/**
 * Compile files from _scss into both _site/css (for live injecting) and site (for future jekyll builds)
 */
gulp.task('sass', function() {
  return gulp
    .src('library/css/*.scss')
    .pipe(maps.init())
    .pipe(
      sass({
        onError: browserSync.notify
      })
    )
    .pipe(
      prefix(['last 15 versions', '> 1%', 'ie 8', 'ie 7'], { cascade: true })
    )
    .pipe(nano())
    .pipe(maps.write('./'))
    .pipe(gulp.dest('library/css'))
    .pipe(browserSync.reload({ stream: true }))
    .pipe(gulp.dest('library/css'));
});
gulp.task('purgecss', () => {
  return gulp
    .src('library/css/*.css')
    .pipe(
      purgecss({
        content: ['_site/**/*.html']
      })
    )
    .pipe(gulp.dest('library/css'));
});
/**
 * Compile files from js into both _site/js (for live injecting) and site (for future jekyll builds)
 */
gulp.task('js', function() {
  return gulp
    .src(['library/js/*.js', '!library/js/*.min.js'])
    .pipe(uglify())
    .pipe(rename({ suffix: '.min' }))
    .pipe(gulp.dest('library/js'))
    .pipe(browserSync.reload({ stream: true }))
    .pipe(gulp.dest('js'));
});
/**
 * Wait for jekyll-build, then launch the Server
 */
gulp.task(
  'browser-sync',
  gulp.series('sass', 'jekyll-build', function() {
    browserSync({
      server: {
        baseDir: '_site'
      }
    });
  })
);
/**
 * Watch scss files for changes & recompile
 * Watch html/md files, run jekyll & reload BrowserSync
 */
gulp.task('watch', function() {
  gulp.watch('library/css/*.scss', gulp.series('sass', 'purgecss'));
  gulp.watch(['library/js/*.js','!library/js/*.min.js'], gulp.series('js'));
  // gulp.watch(['*.html', '_layouts/*.html', '_posts/*'], ['jekyll-rebuild']);
});

gulp.task('imagemin', function() {
  return gulp
    .src('library/images/**/*')
    .pipe(
      imagemin({
        progressive: true
        // use: [pngquant()]
      })
    )
    .pipe(gulp.dest('library/images/'));
});

/**
 * Default task, running just `gulp` will compile the sass,
 * compile the jekyll site, launch BrowserSync & watch files.
 */
gulp.task('default', gulp.parallel('watch', 'jekyll-serve'));