add new Scheduler Class

Signed-off-by: Emma Indal <emma.indahl@gmail.com>

plugins/search-backend-node/src/Scheduler.ts

@@ -0,0 +1,75 @@
+/*
+ * Copyright 2021 Spotify AB
+ *
+ * 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.
+ */
+
+import { Logger } from 'winston';
+
+type TaskEnvelope = {
+  task: Function;
+  interval: number;
+};
+
+/**
+ * TODO: coordination, error handling
+ */
+
+export class Scheduler {
+  private logger: Logger;
+  private schedule: TaskEnvelope[];
+  private intervalTimeouts: NodeJS.Timeout[] = [];
+
+  constructor({ logger }: { logger: Logger }) {
+    this.logger = logger;
+    this.schedule = [];
+  }
+
+  /**
+   * Adds each task and interval to the schedule
+   *
+   */
+  addToSchedule(task: Function, interval: number) {
+    if (this.intervalTimeouts.length) {
+      throw new Error(
+        'Cannot add task to schedule that has already been started.',
+      );
+    }
+    this.schedule.push({ task, interval });
+  }
+
+  /**
+   * Starts the scheduling process for each task
+   */
+  start() {
+    this.logger.info('Starting all scheduled search tasks.');
+    this.schedule.forEach(({ task, interval }) => {
+      this.intervalTimeouts.push(
+        setInterval(() => {
+          task();
+        }, interval),
+      );
+    });
+  }
+
+  /**
+   * Stop all scheduled tasks.
+   */
+  stop() {
+    this.logger.info('Stopping all scheduled search tasks.');
+    this.intervalTimeouts.forEach(timeout => {
+      clearInterval(timeout);
+    });
+    this.intervalTimeouts = [];
+  }
+}