GUACAMOLE-1204: Add generic, listener-driven event system.

guacamole-common-js/src/main/webapp/modules/Event.js

@@ -0,0 +1,243 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+var Guacamole = Guacamole || {};
+
+/**
+ * An arbitrary event, emitted by a {@link Guacamole.Event.Target}. This object
+ * should normally serve as the base class for a different object that is more
+ * specific to the event type.
+ *
+ * @constructor
+ * @param {String} type
+ *     The unique name of this event type.
+ */
+Guacamole.Event = function Event(type) {
+
+    /**
+     * The unique name of this event type.
+     *
+     * @type {String}
+     */
+    this.type = type;
+
+    /**
+     * An arbitrary timestamp in milliseconds, indicating this event's
+     * position in time relative to other events.
+     *
+     * @type {Number}
+     */
+    this.timestamp = new Date().getTime();
+
+    /**
+     * Returns the number of milliseconds elapsed since this event was created.
+     *
+     * @return {Number}
+     *     The number of milliseconds elapsed since this event was created.
+     */
+    this.getAge = function getAge() {
+        return new Date().getTime() - this.timestamp;
+    };
+
+    /**
+     * Requests that the legacy event handler associated with this event be
+     * invoked on the given event target. This function will be invoked
+     * automatically by implementations of {@link Guacamole.Event.Target}
+     * whenever {@link Guacamole.Event.Target#emit emit()} is invoked.
+     * <p>
+     * Older versions of Guacamole relied on single event handlers with the
+     * prefix "on", such as "onmousedown" or "onkeyup". If a Guacamole.Event
+     * implementation is replacing the event previously represented by one of
+     * these handlers, this function gives the implementation the opportunity
+     * to provide backward compatibility with the old handler.
+     * <p>
+     * Unless overridden, this function does nothing.
+     *
+     * @param {Guacamole.Event.Target} eventTarget
+     *     The {@link Guacamole.Event.Target} that emitted this event.
+     */
+    this.invokeLegacyHandler = function invokeLegacyHandler(eventTarget) {
+        // Do nothing
+    };
+
+};
+
+/**
+ * A {@link Guacamole.Event} that relates to one or more DOM events. Continued
+ * propagation and default behavior of the related DOM events may be prevented
+ * with {@link Guacamole.Event.DOMEvent#stopPropagation stopPropagation()} and
+ * {@link Guacamole.Event.DOMEvent#preventDefault preventDefault()}
+ * respectively.
+ *
+ * @constructor
+ * @augments Guacamole.Event
+ *
+ * @param {String} type
+ *     The unique name of this event type.
+ *
+ * @param {Event[]} events
+ *     The DOM events that are related to this event. Future calls to
+ *     {@link Guacamole.Event.DOMEvent#preventDefault preventDefault()} and
+ *     {@link Guacamole.Event.DOMEvent#stopPropagation stopPropagation()} will
+ *     affect these events.
+ */
+Guacamole.Event.DOMEvent = function DOMEvent(type, events) {
+
+    Guacamole.Event.call(this, type);
+
+    /**
+     * Requests that the default behavior of related DOM events be prevented.
+     * Whether this request will be honored by the browser depends on the
+     * nature of those events and the timing of the request.
+     */
+    this.preventDefault = function preventDefault() {
+        events.forEach(function applyPreventDefault(event) {
+            if (event.preventDefault) event.preventDefault();
+            event.returnValue = false;
+        });
+    };
+
+    /**
+     * Stops further propagation of related events through the DOM. Only events
+     * that are directly related to this event will be stopped.
+     */
+    this.stopPropagation = function stopPropagation() {
+        events.forEach(function applyStopPropagation(event) {
+            event.stopPropagation();
+        });
+    };
+
+};
+
+/**
+ * An object which can dispatch {@link Guacamole.Event} objects. Listeners
+ * registered with {@link Guacamole.Event.Target#on on()} will automatically
+ * be invoked based on the type of {@link Guacamole.Event} passed to
+ * {@link Guacamole.Event.Target#dispatch dispatch()}. It is normally
+ * subclasses of Guacamole.Event.Target that will dispatch events, and usages
+ * of those subclasses that will catch dispatched events with on().
+ *
+ * @constructor
+ */
+Guacamole.Event.Target = function Target() {
+
+    /**
+     * A callback function which handles an event dispatched by an event
+     * target.
+     *
+     * @callback Guacamole.Event.Target~listener
+     * @param {Guacamole.Event} event
+     *     The event that was dispatched.
+     *
+     * @param {Guacamole.Event.Target} target
+     *     The object that dispatched the event.
+     */
+
+    /**
+     * All listeners (callback functions) registered for each event type passed
+     * to {@link Guacamole.Event.Targer#on on()}.
+     *
+     * @private
+     * @type {Object.<String, Guacamole.Event.Target~listener[]>}
+     */
+    var listeners = {};
+
+    /**
+     * Registers a listener for events having the given type, as dictated by
+     * the {@link Guacamole.Event#type type} property of {@link Guacamole.Event}
+     * provided to {@link Guacamole.Event.Target#dispatch dispatch()}.
+     *
+     * @param {String} type
+     *     The unique name of this event type.
+     *
+     * @param {Guacamole.Event.Target~listener} listener
+     *     The function to invoke when an event having the given type is
+     *     dispatched. The {@link Guacamole.Event} object provided to
+     *     {@link Guacamole.Event.Target#dispatch dispatch()} will be passed to
+     *     this function, along with the dispatching Guacamole.Event.Target.
+     */
+    this.on = function on(type, listener) {
+
+        var relevantListeners = listeners[type];
+        if (!relevantListeners)
+            listeners[type] = relevantListeners = [];
+
+        relevantListeners.push(listener);
+
+    };
+
+    /**
+     * Dispatches the given event, invoking all event handlers registered with
+     * this Guacamole.Event.Target for that event's
+     * {@link Guacamole.Event#type type}.
+     *
+     * @param {Guacamole.Event} event
+     *     The event to dispatch.
+     */
+    this.dispatch = function dispatch(event) {
+
+        // Invoke any relevant legacy handler for the event
+        event.invokeLegacyHandler(this);
+
+        // Invoke all registered listeners
+        var relevantListeners = listeners[event.type];
+        if (relevantListeners) {
+            for (var i = 0; i < relevantListeners.length; i++) {
+                relevantListeners[i](event, this);
+            }
+        }
+
+    };
+
+    /**
+     * Unregisters a listener that was previously registered with
+     * {@link Guacamole.Event.Target#on on()}. If no such listener was
+     * registered, this function has no effect. If multiple copies of the same
+     * listener were registered, the first listener still registered will be
+     * removerd.
+     *
+     * @param {String} type
+     *     The unique name of the event type handled by the listener being
+     *     removed.
+     *
+     * @param {Guacamole.Event.Target~listener} listener
+     *     The listener function previously provided to
+     *     {@link Guacamole.Event.Target#on on()}.
+     *
+     * @returns {Boolean}
+     *     true if the specified listener was removed, false otherwise.
+     */
+    this.off = function off(type, listener) {
+
+        var relevantListeners = listeners[type];
+        if (!relevantListeners)
+            return false;
+
+        for (var i = 0; i < relevantListeners.length; i++) {
+            if (relevantListeners[i] === listener) {
+                relevantListeners.splice(i, 1);
+                return true;
+            }
+        }
+
+        return false;
+
+    };
+
+};