/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Tobias Koppers @sokra
*/
var memoize = function(fn) {
		var memo;
		return function () {
			if (typeof memo === "undefined") memo = fn.apply(this, arguments);
			return memo;
		};
	},
	getHeadElement = memoize(function () {
		return document.head || document.getElementsByTagName("head")[0];
	}),
	styleElementsInsertedAtTop = [];

module.exports = function(list, options) {
	if(typeof DEBUG !== "undefined" && DEBUG) {
		if(typeof document !== "object") throw new Error("The style-loader cannot be used in a non-browser environment");
	}

	options = options || {};
	// Force single-tag solution on IE6-9, which has a hard limit on the # of <style>
	// tags it will allow on a page
  options.singleton = false;

	// By default, add <style> tags to the bottom of <head>.
	if (typeof options.insertAt === "undefined") options.insertAt = "bottom";

	var styles = listToStyles(list);
	addStylesToDom(styles, options);
}

function addStylesToDom(styles, options) {
	for(var i = 0; i < styles.length; i++) {
		var item = styles[i];
    for(var j = 0; j < item.parts.length; j++) {
      addStyle(item.parts[j], options);
    }
	}
}

function listToStyles(list) {
	var styles = [];
	var newStyles = {};
	for(var i = 0; i < list.length; i++) {
		var item = list[i];
		var id = item[0];
		var css = item[1];
		var media = item[2];
		var sourceMap = item[3];
		var part = {css: css, media: media, sourceMap: sourceMap};
		if(!newStyles[id])
			styles.push(newStyles[id] = {id: id, parts: [part]});
		else
			newStyles[id].parts.push(part);
	}
	return styles;
}

function insertStyleElement(options, styleElement) {
	var head = getHeadElement();
	var lastStyleElementInsertedAtTop = styleElementsInsertedAtTop[styleElementsInsertedAtTop.length - 1];
	if (options.insertAt === "top") {
		if(!lastStyleElementInsertedAtTop) {
			head.insertBefore(styleElement, head.firstChild);
		} else if(lastStyleElementInsertedAtTop.nextSibling) {
			head.insertBefore(styleElement, lastStyleElementInsertedAtTop.nextSibling);
		} else {
			head.appendChild(styleElement);
		}
		styleElementsInsertedAtTop.push(styleElement);
	} else if (options.insertAt === "bottom") {
		head.appendChild(styleElement);
	} else {
		throw new Error("Invalid value for parameter 'insertAt'. Must be 'top' or 'bottom'.");
	}
}

function createStyleElement(options) {
	var styleElement = document.createElement("style");
	styleElement.type = "text/css";
	insertStyleElement(options, styleElement);
	return styleElement;
}

function addStyle(obj, options) {
	var styleElement, update, remove;

  styleElement = createStyleElement(options);
  update = applyToTag.bind(null, styleElement);
	update(obj);
}

function applyToTag(styleElement, obj) {
	var css = obj.css;
	var media = obj.media;

	if(media) {
		styleElement.setAttribute("media", media)
	}

	if(styleElement.styleSheet) {
		styleElement.styleSheet.cssText = css;
	} else {
		while(styleElement.firstChild) {
			styleElement.removeChild(styleElement.firstChild);
		}
		styleElement.appendChild(document.createTextNode(css));
	}
}
