gulpfile.js

var gulp       = require('gulp');
var concat     = require('gulp-concat');
var coffee     = require('gulp-coffee');
var uglify     = require('gulp-uglify');
var sass       = require('gulp-sass');
var cssnano    = require('gulp-cssnano');
var rename     = require('gulp-rename');
var imagemin   = require('gulp-imagemin');
var htmlclean  = require('gulp-htmlclean');
var deporder   = require('gulp-deporder');
var stripdebug = require('gulp-strip-debug');
var del        = require('del');
var connect    = require('gulp-connect');
var watch      = require('gulp-watch');

gulp.task('clean:dist', function(pFnDone) {
	del(['dist/**', '!dist', '!dist/.gitkeep']);
	pFnDone();
});

gulp.task('clean:css', function(pFnDone) {
	del(['dist/css/**']);
	pFnDone();
});

gulp.task('clean:image', function(pFnDone) {
	del(['dist/img/**']);
	pFnDone();
});

gulp.task('clean:js', function(pFnDone) {
	del(['dist/js/**']);
	pFnDone();
});

gulp.task('clean:lib', function(pFnDone) {
	del(['dist/lib/**']);
	pFnDone();
});

gulp.task('clean:html', function(pFnDone) {
	del(['dist/**/*.+(html|htm)', '!dist/lib', '!dist/lib/**/*.+(html|htm)']);
	pFnDone();
});

gulp.task('image', gulp.series('clean:image', function imageBuild(pFnDone) {
	!(gulp.src('app/img/**/*.+(png|jpg|jpeg|gif|svg)')
		.pipe(imagemin({
			optimizationLeve : 5,
			interlaced: true
		}))
		.pipe(gulp.dest('dist/img'))
	);
	pFnDone();
}));

gulp.task('sass', function(pFnDone) {
	!(gulp.src('app/scss/**/*.scss')
		.pipe(sass())
		.pipe(concat('scssStyles.css'))
		.pipe(gulp.dest('app/css'))
	);
	pFnDone();
});

gulp.task('css', gulp.series('clean:css', function cssBuild(pFnDone) {
	!(gulp.src('app/css/**/*.css')
		.pipe(concat('styles.css'))
		.pipe(gulp.dest('dist/css'))
		.pipe(rename('styles.min.css'))
		.pipe(cssnano())
		.pipe(gulp.dest('dist/css'))
	);
	pFnDone();
}));

gulp.task('coffee', function(pFnDone) {
	!(gulp.src('app/coffee/**/*.coffee')
		.pipe(coffee())
		.pipe(concat('coffeeScripts.js'))
		.pipe(gulp.dest('app/js'))
	);
	pFnDone();
});

gulp.task('js', gulp.series('clean:js', function jsBuild(pFnDone) {
	!(gulp.src('app/js/*.js')
		.pipe(deporder()) // Ensure dependency order
		.pipe(concat('scripts.js'))
		.pipe(gulp.dest('dist/js'))
		.pipe(rename('scripts.min.js'))
		// .pipe(stripdebug()) // Remove debug lines
		.pipe(uglify())
		.pipe(gulp.dest('dist/js'))
	);
	pFnDone();
}));

gulp.task('lib', gulp.series('clean:lib', function libBuild(pFnDone) {
	!(gulp.src(['app/lib/**/*', '!app/lib/.gitkeep'])
		.pipe(gulp.dest('dist/lib'))
	);
	pFnDone();
}));

gulp.task('html', gulp.series('clean:html', function htmlBuild(pFnDone) {
	!(gulp.src(['app/**/*.+(html|htm)', '!app/lib/**'])
		// .pipe(htmlclean()) // Clean HTML (comments, unnecessary whitespaces / attributes, etc.)
		.pipe(gulp.dest('dist'))
	);
	pFnDone();
}));

gulp.task('watch', function(pFnDone) {
	gulp.watch('app/img/**/*.+(png|jpg|jpeg|gif|svg)', gulp.series('image'))
	gulp.watch('app/scss/**/*.scss', gulp.series('sass'));
	gulp.watch('app/css/**/*.css', gulp.series('css'));
	gulp.watch('app/coffee/**/*.coffee', gulp.series('coffee'));
	gulp.watch('app/js/**/*.js', gulp.series('js'));
	gulp.watch(['app/lib/**/*', '!app/lib/.gitkeep'], gulp.series('lib'));
	gulp.watch(['app/**/*.+(html|htm)', '!app/lib'], gulp.series('html'));
	watch('dist/**/*', { ignoreInitial: false }).pipe(connect.reload());
	pFnDone();
});

gulp.task('connect', function(pFnDone) {
	connect.server({
		root: 'dist/',
		livereload: true
	});
	pFnDone();
});

gulp.task('build', gulp.series('clean:dist', gulp.parallel('image', gulp.series('sass','css'), gulp.series('coffee', 'js'), 'lib', 'html')));

gulp.task('dev', gulp.parallel(gulp.series('build', 'watch'), 'connect'));

gulp.task('default', gulp.series('build'));