ast.js

function Stack () {
		this.next = this
		this.prev = this
		this.length = 0
	}

	Stack.prototype = {
		/**
		 * @param {Object} node
		 * @param {Object} before
		 * @return {Object}
		 */
		push: function push (node) {
			node.next = this
			node.prev = this.prev
			this.prev.next = node
			this.prev = node
			this.length++

			return node
		},
		/**
		 * @param {Object} node
		 * @return {Object}
		 */
		pop: function pop () {
			if (this.length === 0)
				return

			this.next.prev = this.prev
			this.prev.next = this.next
			this.length--

			return this.prev
		},
		/**
		 * @param {function} callback
		 */
		forEach: function forEach (callback) {
			for (var i = 0, node = this; i < this.length; ++i)
				callback(node = node.next, i)
		}
	}

	var children = new Stack
	var stack = new Stack

	function Node (rule, body) {
		this.rule = rule
		this.body = body
		this.children = null
		this.next = null
		this.prev = null
	}

	function plugin (context, content, selectors, parents, line, column, length, id) {
		var selector = selectors.join(',')

		switch (context) {
			case 1:
				if (content.charCodeAt(0) !== 64)
					return
			case 2:
			case 3:
				switch (id) {
					// @font
					// @keyframe
					case 102:
					case 107:
					// @media
					case 109:
						// @at-rule body
						if (selector.charCodeAt(0) !== 64)
							return
				}

				var node = new Node(selector, content)

				if (parents.join(',').length === 0) {
					stack.push(node).children = children
					children = new Stack
				} else {
					children.push(node)
				}
				break
			case -2:
				return stack
		}
	}