Start responding to dynamic stylesheet changes

This mechanism will only be triggered by changes to the stylesheet
tiddlers themselves, and not to any dependencies that they might have.
It'll stay that way for a while.

The next thing is making the theme manager actually switch themes,
forcing the right wiki change events to make the stylesheet manager
update itself

core/modules/startup.js

@@ -89,21 +89,9 @@ exports.startup = function() {
 		document.addEventListener("tw-clear-password",function(event) {
 			$tw.crypto.setPassword(null);
 		});
-		// Unpack the current theme tiddlers
-		$tw.wiki.unpackPluginTiddlers("theme");
-		// Apply stylesheets
-		var stylesheetTiddlers = $tw.wiki.filterTiddlers("[is[shadow]tag[$:/tags/stylesheet]]");
-		$tw.utils.each(stylesheetTiddlers,function(title,index) {
-			// Stylesheets don't refresh, yet
-			var parser = $tw.wiki.parseTiddler(title),
-				renderTree = new $tw.WikiRenderTree(parser,{wiki: $tw.wiki});
-			renderTree.execute({tiddlerTitle: title});
-			var styleNode = document.createElement("style");
-			styleNode.type = "text/css";
-			var text = renderTree.render("text/plain");
-			styleNode.appendChild(document.createTextNode(text));
-			document.getElementsByTagName("head")[0].appendChild(styleNode);
-		});
+		// Kick off the theme and the stylesheet manager
+		$tw.themeManager = new $tw.ThemeManager($tw.wiki);
+		$tw.stylesheetManager = new $tw.utils.StylesheetManager($tw.wiki);
 		// If we're being viewed on a data: URI then give instructions for how to save
 		if(document.location.protocol === "data:") {
 			$tw.utils.dispatchCustomEvent(document,"tw-modal",{

core/modules/themes.js

@@ -0,0 +1,23 @@
+/*\
+title: $:/core/modules/themes.js
+type: application/javascript
+module-type: global
+
+Manages themes and styling.
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+function ThemeManager(wiki) {
+	this.wiki = wiki;
+	// Unpack the current theme tiddlers
+	$tw.wiki.unpackPluginTiddlers("theme");
+}
+
+exports.ThemeManager = ThemeManager;
+
+})();

core/modules/utils/dom/styles.js

@@ -0,0 +1,78 @@
+/*\
+title: $:/core/modules/utils/styles.js
+type: application/javascript
+module-type: utils
+
+The stylesheet manager automatically renders any tiddlers tagged "$:/tags/stylesheet" as HTML style elements.
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+var STYLESHEET_ID_PREFIX = "tw-tiddler-stylesheet-",
+	STYLESHEET_TAG = "$:/tags/stylesheet";
+
+function StylesheetManager(wiki) {
+	this.wiki = wiki;
+	this.stylesheets = {}; // Hashmap of currently rendered stylesheets
+	// Apply initial stylesheets
+	var self = this,
+		stylesheetTiddlers = this.wiki.filterTiddlers("[is[shadow]!has[draft.of]tag[" + STYLESHEET_TAG + "]]");
+	$tw.utils.each(stylesheetTiddlers,function(title,index) {
+		self.addStylesheet(title);
+	});
+	// Listen out for changes
+	this.wiki.addEventListener("change",function(changes) {
+		self.handleTiddlerChanges(changes);
+	});
+}
+
+StylesheetManager.prototype.addStylesheet = function(title) {
+	// Record the stylesheet in the hashmap
+	this.stylesheets[title] = true;
+	// Parse the tiddler and render as plain text
+	var parser = this.wiki.parseTiddler(title),
+		renderTree = new $tw.WikiRenderTree(parser,{wiki: this.wiki});
+	renderTree.execute({tiddlerTitle: title});
+	var text = renderTree.render("text/plain");
+	// Create a style element and put it in the document
+	var styleNode = document.createElement("style");
+	styleNode.setAttribute("type","text/css");
+	styleNode.setAttribute("id",STYLESHEET_ID_PREFIX + title);
+	styleNode.appendChild(document.createTextNode(text));
+	document.getElementsByTagName("head")[0].appendChild(styleNode);
+};
+
+StylesheetManager.prototype.removeStylesheet = function(title) {
+	// Remove the stylesheet from the hashmap
+	if($tw.utils.hop(this.stylesheets,title)) {
+		delete this.stylesheets[title];
+	}
+	// Remove the stylesheet from the document
+	var styleNode = document.getElementById(STYLESHEET_ID_PREFIX + title);
+	if(styleNode) {
+		styleNode.parentNode.removeChild(styleNode);
+	}
+};
+
+StylesheetManager.prototype.handleTiddlerChanges = function(changes) {
+	var self = this;
+	$tw.utils.each(changes,function(change,title) {
+		// Remove any existing stylesheet for the changed tiddler
+		if($tw.utils.hop(self.stylesheets,title)) {
+			self.removeStylesheet(title);
+		}
+		// Add the stylesheet if it is tagged and not a draft
+		var tiddler = self.wiki.getTiddler(title);
+		if(tiddler && tiddler.hasTag(STYLESHEET_TAG) && !tiddler.hasField("draft.of")) {
+			self.addStylesheet(title);
+		}
+	});
+};
+
+exports.StylesheetManager = StylesheetManager;
+
+})();