index.js

var path = require('path');
var fs = require('fs');
var EOL = require('os').EOL;

var through = require('through2');
var gutil = require('gulp-util');
var glob = require('glob');

module.exports = function(options) {
	options = options || {};

	var startReg = /<!--\s*build:(\w+)(?:\(([^\)]+?)\))?\s+(\/?([^\s]+?))\s*-->/gim;
	var endReg = /<!--\s*endbuild\s*-->/gim;
	var jsReg = /<\s*script\s+.*?src\s*=\s*"([^"]+?)".*?><\s*\/\s*script\s*>/gi;
	var cssReg = /<\s*link\s+.*?href\s*=\s*"([^"]+)".*?>/gi;
	var basePath, mainPath, mainName, alternatePath;

	function createFile(name, content) {
		return new gutil.File({
			path: path.join(path.relative(basePath, mainPath), name),
			contents: new Buffer(content)
		})
	}

	function getBlockType(content) {
		return jsReg.test(content) ? 'js' : 'css';
	}

	function getFiles(content, reg) {
		var paths = [];
		var files = [];

		content
			.replace(/<!--(?:(?:.|\r|\n)*?)-->/gim, '')
			.replace(reg, function (a, b) {
				var filePath = path.resolve(path.join(alternatePath || mainPath, b));

				if (options.assetsDir)
					filePath = path.resolve(path.join(options.assetsDir, path.relative(basePath, filePath)));

				paths.push(filePath);
			});

		for (var i = 0, l = paths.length; i < l; ++i) {
			var filepath = glob.sync(paths[i])[0];
			files.push(new gutil.File({
				path: filepath,
				contents: fs.readFileSync(filepath)
			}));
		}

		return files;
	}

	function concat(files, name) {
		var buffer = [];

		files.forEach(function(file) {
			buffer.push(String(file.contents));
		});

		return createFile(name, buffer.join(EOL));
	}

	function processTask(index, tasks, name, files, callback) {
		var newFiles = [];

		if (tasks[index] == 'concat') {
			newFiles = [concat(files, name)];
		}
		else {
			var stream = tasks[index];

			function write(file) {
				newFiles.push(file);
			}

			stream.on('data', write);
			files.forEach(function(file) {
				stream.write(file);
			});
			stream.removeListener('data', write);
		}

		if (tasks[++index])
			processTask(index, tasks, name, newFiles, callback);
		else
			newFiles.forEach(callback);
	}

	function process(name, files, pipelineId, callback) {
		var tasks = options[pipelineId] || [];
		if (tasks.indexOf('concat') == -1)
			tasks.unshift('concat');

		processTask(0, tasks, name, files, callback);
	}

	function processHtml(content, push, callback) {
		var html = [];
		var sections = content.split(endReg);

		for (var i = 0, l = sections.length; i < l; ++i)
			if (sections[i].match(startReg)) {
				var section = sections[i].split(startReg);
				alternatePath = section[2];

				html.push(section[0]);

				if (getBlockType(section[5]) == 'js')
					process(section[4], getFiles(section[5], jsReg), section[1], function(name, file) {
						push(file);
						if (path.extname(file.path) == '.js')
							html.push('<script src="' + name.replace(path.basename(name), path.basename(file.path)) + '"></script>');
					}.bind(this, section[3]));
				else
					process(section[4], getFiles(section[5], cssReg), section[1], function(name, file) {
						// Ulgy hack in order to support media and id attribute on our stylesheets
						var cssExtraAttrReg = /(?:media|id)=['"][^"']*['"]/g;
						var extraAttr = [];
						var match;
						while((match = cssExtraAttrReg.exec(section[5])) !== null) {
							extraAttr.push(match[0]);
						}
						var extraAttrStr = extraAttr.join(' ');

						push(file);
						html.push('<link rel="stylesheet" href="' + name.replace(path.basename(name), path.basename(file.path)) + '" ' + extraAttrStr +'/>');
					}.bind(this, section[3]));
			}
			else
				html.push(sections[i]);

		process(mainName, [createFile(mainName, html.join(''))], 'html', function(file) {
			push(file);
			callback();
		});
	}

	return through.obj(function(file, enc, callback) {
		if (file.isNull()) {
			this.push(file); // Do nothing if no contents
			callback();
		}
		else if (file.isStream()) {
			this.emit('error', new gutil.PluginError('gulp-usemin', 'Streams are not supported!'));
			callback();
		}
		else {
			basePath = file.base;
			mainPath = path.dirname(file.path);
			mainName = path.basename(file.path);

			processHtml(String(file.contents), this.push.bind(this), callback);
		}
	});
};