Introduce background actions

Background actions are invoked when the results of a filter change.

The sample background action is just for demo purposes to show how an automatic dark/light mode feature would be powered

core/modules/background-actions.js

@@ -0,0 +1,117 @@
+/*\
+title: $:/core/modules/background-actions.js
+type: application/javascript
+module-type: global
+
+Class to dispatch actions when filters change
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+function BackgroundActionDispatcher(filterTracker,wiki) {
+	var self = this;
+	this.filterTracker = filterTracker;
+	this.wiki = wiki;
+	this.nextTrackedFilterId = 1;
+	this.trackedFilters = Object.create(null); // Hashmap by id
+	// Track the filter for the background actions
+	this.filterTracker.track({
+		filterString: "[all[tiddlers+shadows]tag[$:/tags/BackgroundAction]!is[draft]]",
+		fnEnter: function fnEnter(title) {
+			return self.trackFilter(title);
+		},
+		fnLeave: function fnLeave(title,enterValue) {
+			self.untrackFilter(enterValue);
+		},
+		fnChange: function fnChange(title,enterValue) {
+			self.untrackFilter(enterValue);
+			return self.trackFilter(title);
+		},
+		fnProcess: function fnProcess(changes) {
+			self.process(changes);
+		}
+	});
+}
+
+BackgroundActionDispatcher.prototype.trackFilter = function(title) {
+	var tiddler = this.wiki.getTiddler(title),
+		id = this.nextTrackedFilterId++,
+		tracker = new BackgroundActionTracker({
+			wiki: this.wiki,
+			title: title,
+			trackFilter: tiddler.fields["track-filter"],
+			actions: tiddler.fields.text
+		});
+	this.trackedFilters[id] = tracker;
+	return id;
+};
+
+BackgroundActionDispatcher.prototype.untrackFilter = function(enterValue) {
+	var tracker = this.trackedFilters[enterValue];
+	if(tracker) {
+		tracker.destroy();
+	}
+	delete this.trackedFilters[enterValue];
+};
+
+BackgroundActionDispatcher.prototype.process = function(changes) {
+	for(var id in this.trackedFilters) {
+		this.trackedFilters[id].process(changes);
+	}
+};
+
+/*
+Represents an individual tracked filter. Options include:
+wiki: wiki to use
+title: title of the tiddler being tracked
+trackFilter: filter string to track changes
+actions: actions to be executed when the filter changes
+*/
+function BackgroundActionTracker(options) {
+	var self = this;
+	this.wiki = options.wiki;
+	this.title = options.title;
+	this.trackFilter = options.trackFilter;
+	this.actions = options.actions
+	this.filterTracker = new $tw.FilterTracker(this.wiki);
+	this.hasChanged = false;
+	this.trackerID = this.filterTracker.track({
+		filterString: this.trackFilter,
+		fnEnter: function(title) {
+			self.hasChanged = true;
+		},
+		fnLeave: function(title,enterValue) {
+			self.hasChanged = true;
+		},
+		fnProcess: function(changes) {
+			if(self.hasChanged) {
+				self.hasChanged = false;
+				self.wiki.invokeActionString(
+					self.actions,
+					null,
+					{
+						title: self.title
+					},{
+						parentWidget: $tw.rootWidget
+					}
+				);
+			}
+		}
+	});
+}
+
+BackgroundActionTracker.prototype.process = function(changes) {
+	this.filterTracker.handleChangeEvent(changes);
+};
+
+BackgroundActionTracker.prototype.destroy = function() {
+	this.filterTracker.untrack(this.trackerID);
+};
+
+exports.BackgroundActionDispatcher = BackgroundActionDispatcher;
+
+})();

core/modules/startup/load-modules.js

@@ -49,6 +49,8 @@ exports.startup = function() {
 	$tw.wiki.addEventListener("change",function(changes) {
 		$tw.filterTracker.handleChangeEvent(changes);
 	});
+	// Kick off the background action dispatcher
+	$tw.backgroundActionDispatcher = new $tw.BackgroundActionDispatcher($tw.filterTracker,$tw.wiki);
 };
 
 })();

core/wiki/SampleBackgroundAction.tid

@@ -0,0 +1,9 @@
+title: SampleBackgroundAction
+tags: $:/tags/BackgroundAction
+track-filter: [{$:/info/browser/darkmode}]
+
+<%if [{$:/info/browser/darkmode}match[no]] %>
+<$action-setfield $tiddler="$:/palette" text="$:/palettes/Vanilla"/>
+<%else%>
+<$action-setfield $tiddler="$:/palette" text="$:/palettes/SolarizedDark"/>
+<%endif%>