update timed loader to use class composition

src/loaders/TimedApiBasedRepositoryLoader.ts

@@ -0,0 +1,54 @@
+import { RepositoryLoader } from "./RepositoryLoader";
+
+// Ideas to break this into smaller pieces in the future:
+// Have one repository data loader running for each supported system
+// Each data loader independently updates data based on frequency of usage
+
+// Notes on this: we only need to reload ETA data frequently
+// Other data can be reloaded periodically
+// Detailed list:
+// - ETA: reload frequently or switch to write-through approach
+// - Shuttles: reload every minute
+// - Routes: reload every few minutes
+// - Stops: reload every few minutes
+// - OrderedStops: reload every few minutes
+// - Systems: reload once a day
+
+export class TimedApiBasedRepositoryLoader {
+  private shouldBeRunning: boolean = false;
+  private timer: any;
+
+  readonly timeout = 10000;
+
+  constructor(
+    public loader: RepositoryLoader,
+  ) {
+    this.startFetchDataAndUpdate = this.startFetchDataAndUpdate.bind(this);
+  }
+
+  public async start() {
+    if (this.shouldBeRunning) {
+      console.warn("DataLoader timer is already running");
+      return;
+    }
+
+    this.shouldBeRunning = true;
+    await this.startFetchDataAndUpdate();
+  }
+
+  public stop() {
+    this.shouldBeRunning = false;
+  }
+
+  private async startFetchDataAndUpdate() {
+    if (!this.shouldBeRunning) return;
+
+    try {
+      await this.loader.fetchAndUpdateAll();
+    } catch (e) {
+      console.error(e);
+    }
+
+    this.timer = setTimeout(this.startFetchDataAndUpdate, this.timeout);
+  }
+}