ToggleEnterpriseModel: new GrainJS model to handle changes to config API

Patterned after TelemetryModel.ts

app/client/models/ToggleEnterpriseModel.ts

@@ -0,0 +1,44 @@
+import {getHomeUrl} from 'app/client/models/AppModel';
+import {Disposable, Observable} from "grainjs";
+import {ConfigAPI} from 'app/common/ConfigAPI';
+import {delay} from 'app/common/delay';
+
+export class ToggleEnterpriseModel extends Disposable {
+  public readonly edition: Observable<string | null> = Observable.create(this, null);
+  private readonly _configAPI: ConfigAPI = new ConfigAPI(getHomeUrl());
+
+  public async fetchEnterpriseToggle(): Promise<void> {
+    const edition = await this._configAPI.getValue('edition');
+    this.edition.set(edition);
+  }
+
+  public async updateEnterpriseToggle(edition: string): Promise<void> {
+    // We may be restarting the server, so these requests may well
+    // fail if done in quick succession.
+    await retryOnNetworkError(() => this._configAPI.setValue({edition}));
+    this.edition.set(edition);
+    await retryOnNetworkError(() => this._configAPI.restartServer());
+  }
+}
+
+// Copied from DocPageModel.ts
+const reconnectIntervals = [1000, 1000, 2000, 5000, 10000];
+async function retryOnNetworkError<R>(func: () => Promise<R>): Promise<R> {
+  for (let attempt = 0; ; attempt++) {
+    try {
+      return await func();
+    } catch (err) {
+      // fetch() promises that network errors are reported as TypeError. We'll accept NetworkError too.
+      if (err.name !== "TypeError" && err.name !== "NetworkError") {
+        throw err;
+      }
+      // We really can't reach the server. Make it known.
+      if (attempt >= reconnectIntervals.length) {
+        throw err;
+      }
+      const reconnectTimeout = reconnectIntervals[attempt];
+      console.warn(`Call to ${func.name} failed, will retry in ${reconnectTimeout} ms`, err);
+      await delay(reconnectTimeout);
+    }
+  }
+}