From 1a6d92ee4e06a5c360006bbe37bc5051698201b1 Mon Sep 17 00:00:00 2001
From: Victor Woeltjen <victor.woeltjen@nasa.gov>
Date: Wed, 24 Jun 2015 12:02:40 -0700
Subject: [PATCH] [Core] Add topic service

Add topic service to support listeners, such as the
mutation listener added for WTD-1329.
---
 platform/core/src/services/Throttle.js | 21 +++++++
 platform/core/src/services/Topic.js    | 87 ++++++++++++++++++++++++++
 2 files changed, 108 insertions(+)
 create mode 100644 platform/core/src/services/Topic.js

diff --git a/platform/core/src/services/Throttle.js b/platform/core/src/services/Throttle.js
index 0c86a403c7..c0493a733a 100644
--- a/platform/core/src/services/Throttle.js
+++ b/platform/core/src/services/Throttle.js
@@ -1,3 +1,24 @@
+/*****************************************************************************
+ * Open MCT Web, Copyright (c) 2014-2015, United States Government
+ * as represented by the Administrator of the National Aeronautics and Space
+ * Administration. All rights reserved.
+ *
+ * Open MCT Web is licensed 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.
+ *
+ * Open MCT Web includes source code licensed under additional open source
+ * licenses. See the Open Source Licenses file (LICENSES.md) included with
+ * this source code distribution or the Licensing information page available
+ * at runtime from the About dialog for additional information.
+ *****************************************************************************/
 /*global define*/
 
 define(
diff --git a/platform/core/src/services/Topic.js b/platform/core/src/services/Topic.js
new file mode 100644
index 0000000000..894274b71c
--- /dev/null
+++ b/platform/core/src/services/Topic.js
@@ -0,0 +1,87 @@
+/*****************************************************************************
+ * Open MCT Web, Copyright (c) 2014-2015, United States Government
+ * as represented by the Administrator of the National Aeronautics and Space
+ * Administration. All rights reserved.
+ *
+ * Open MCT Web is licensed 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.
+ *
+ * Open MCT Web includes source code licensed under additional open source
+ * licenses. See the Open Source Licenses file (LICENSES.md) included with
+ * this source code distribution or the Licensing information page available
+ * at runtime from the About dialog for additional information.
+ *****************************************************************************/
+/*global define*/
+
+define(
+    [],
+    function () {
+        "use strict";
+
+        /**
+         * The `topic` service provides a way to create both named,
+         * shared listeners and anonymous, private listeners.
+         *
+         * Usage:
+         *
+         * ```
+         * var t = topic('foo'); // Use/create a named topic
+         * t.listen(function () { ... });
+         * t.notify({ some: "message" });
+         * ```
+         *
+         * Named topics are shared; multiple calls to `topic`
+         * with the same argument will return a single object instance.
+         * Anonymous topics (where `topic`has been called with no
+         * arguments) are private; each call returns a new instance.
+         *
+         * @returns {Function}
+         */
+        function Topic() {
+            var topics = {};
+
+            function createTopic() {
+                var listeners = [];
+
+                return {
+                    listen: function (listener) {
+                        listeners.push(listener);
+                        return function unlisten() {
+                            listeners = listeners.filter(function (l) {
+                                return l !== listener;
+                            });
+                        };
+                    },
+                    notify: function (message) {
+                        listeners.forEach(function (listener) {
+                            listener(message);
+                        });
+                    }
+                };
+            }
+
+            /**
+             * Use and (if necessary) create a new topic.
+             * @param {string} [key] name of the topic to use
+             */
+            return function (key) {
+                if (arguments.length < 1) {
+                    return createTopic();
+                } else {
+                    topics[key] = topics[key] || createTopic();
+                    return topics[key];
+                }
+            };
+        }
+
+        return Topic;
+    }
+);