Re-implement the event generator as a new-style plugin - Mct4552 (#4620)

Updates Event Generator to ES6 classes and current API.

Co-authored-by: Andrew Henry <akhenry@gmail.com>
Co-authored-by: John Hill <john.c.hill@nasa.gov>

example/eventGenerator/EventTelemetryProvider.js

@@ -0,0 +1,96 @@
+/*****************************************************************************
+ * Open MCT, Copyright (c) 2014-2022, United States Government
+ * as represented by the Administrator of the National Aeronautics and Space
+ * Administration. All rights reserved.
+ *
+ * Open MCT 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 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.
+ *****************************************************************************/
+
+/**
+ * Module defining EventTelemetryProvider. Created by chacskaylo on 06/18/2015.
+ */
+
+import messages from './transcript.json';
+
+class EventTelemetryProvider {
+    constructor() {
+        this.defaultSize = 25;
+    }
+
+    generateData(firstObservedTime, count, startTime, duration, name) {
+        const millisecondsSinceStart = startTime - firstObservedTime;
+        const utc = Math.floor(startTime / duration) * duration;
+        const ind = count % messages.length;
+        const message = messages[ind] + " - [" + millisecondsSinceStart + "]";
+
+        return {
+            name,
+            utc,
+            message
+        };
+    }
+
+    supportsRequest(domainObject) {
+        return domainObject.type === 'eventGenerator';
+    }
+
+    supportsSubscribe(domainObject) {
+        return domainObject.type === 'eventGenerator';
+    }
+
+    subscribe(domainObject, callback) {
+        const duration = domainObject.telemetry.duration * 1000;
+        const firstObservedTime = Date.now();
+        let count = 0;
+
+        const interval = setInterval(() => {
+            const startTime = Date.now();
+            const datum = this.generateData(firstObservedTime, count, startTime, duration, domainObject.name);
+            count += 1;
+            callback(datum);
+        }, duration);
+
+        return function () {
+            clearInterval(interval);
+        };
+    }
+
+    request(domainObject, options) {
+        let start = options.start;
+        const end = Math.min(Date.now(), options.end); // no future values
+        const duration = domainObject.telemetry.duration * 1000;
+        const size = options.size ? options.size : this.defaultSize;
+        const data = [];
+        const firstObservedTime = Date.now();
+        let count = 0;
+
+        if (options.strategy === 'latest' || options.size === 1) {
+            start = end;
+        }
+
+        while (start <= end && data.length < size) {
+            const startTime = Date.now() + count;
+            data.push(this.generateData(firstObservedTime, count, startTime, duration, domainObject.name));
+            start += duration;
+            count += 1;
+        }
+
+        return Promise.resolve(data);
+    }
+}
+
+export default EventTelemetryProvider;