FlexServer: check for updates at startup and every week thereafter

We keep track of checking task so that we can disable it later when we
have a user interface to enable or disable automated version checks.

Author: jordigh

app/server/MergedServer.ts

@@ -194,6 +194,7 @@ export class MergedServer {
       await this.flexServer.finalizePlugins(this.hasComponent("home") ? checkUserContentPort() : null);
       this.flexServer.checkOptionCombinations();
       this.flexServer.summary();
+      this.flexServer.startCheckingForUpdates();
       this.flexServer.ready();
     } catch(e) {
       await this.flexServer.close();

app/server/lib/FlexServer.ts

@@ -76,6 +76,7 @@ import {TagChecker} from 'app/server/lib/TagChecker';
 import {ITelemetry} from 'app/server/lib/Telemetry';
 import {startTestingHooks} from 'app/server/lib/TestingHooks';
 import {getTestLoginSystem} from 'app/server/lib/TestLogin';
+import {compareWithLatest} from 'app/server/lib/updateChecker';
 import {UpdateManager} from 'app/server/lib/UpdateManager';
 import {addUploadRoute} from 'app/server/lib/uploads';
 import {buildWidgetRepository, getWidgetsInPlugins, IWidgetRepository} from 'app/server/lib/WidgetRepository';
@@ -103,6 +104,9 @@ const HEALTH_CHECK_LOG_SHOW_FIRST_N = 10;
 // And we show every Nth health check:
 const HEALTH_CHECK_LOG_SHOW_EVERY_N = 100;
 
+// In milliseconds
+const ONE_WEEK = 7*24*60*60*1000;
+
 // DocID of Grist doc to collect the Welcome questionnaire responses, such
 // as "GristNewUserInfo".
 const DOC_ID_NEW_USER_INFO = process.env.DOC_ID_NEW_USER_INFO;
@@ -200,6 +204,7 @@ export class FlexServer implements GristServer {
   private _jobs?: GristJobs;
   private _emitNotifier = new EmitNotifier();
   private _testPendingNotifications: number = 0;
+  private _intervalCheckID: ReturnType<typeof setInterval>;
 
   constructor(public port: number, public name: string = 'flexServer',
               public readonly options: FlexServerOptions = {}) {
@@ -1983,6 +1988,13 @@ export class FlexServer implements GristServer {
     this.create.addExtraHomeEndpoints(this, this.app);
   }
 
+  public startCheckingForUpdates() {
+    const gristServer = this;
+    compareWithLatest(gristServer);
+    this._intervalCheckID = setInterval(() => {compareWithLatest(gristServer);}, ONE_WEEK);
+    log.debug(`started version check task with ID ${this._intervalCheckID}`);
+  }
+
   // Get the HTML template sent for document pages.
   public async getDocTemplate(): Promise<DocTemplate> {
     const page = await fse.readFile(path.join(getAppPathTo(this.appRoot, 'static'),