added service-worker service

src/app/services/service-worker.service.spec.ts

@@ -0,0 +1,12 @@
+import { TestBed } from '@angular/core/testing';
+
+import { ServiceWorkerService } from './service-worker.service';
+
+xdescribe('ServiceWorkerService', () => {
+  beforeEach(() => TestBed.configureTestingModule({}));
+
+  it('should be created', () => {
+    const service: ServiceWorkerService = TestBed.get(ServiceWorkerService);
+    expect(service).toBeTruthy();
+  });
+});

src/app/services/service-worker.service.ts

@@ -0,0 +1,35 @@
+import { Injectable, ApplicationRef } from '@angular/core';
+import { SwUpdate } from '@angular/service-worker';
+import { first } from 'rxjs/operators';
+import { interval, concat, BehaviorSubject } from 'rxjs';
+
+@Injectable({
+    providedIn: 'root'
+})
+export class ServiceWorkerService {
+
+    newAppVersionIsAvailable = new BehaviorSubject<boolean>(false);
+
+    constructor(appRef: ApplicationRef, updates: SwUpdate) {
+
+        //https://angular.io/guide/service-worker-communications
+        
+        updates.available.subscribe(event => {
+            console.log('current version is', event.current);
+            console.log('available version is', event.available);
+
+            this.newAppVersionIsAvailable.next(true);
+        });
+
+        // Allow the app to stabilize first, before starting polling for updates with `interval()`.
+        const appIsStable$ = appRef.isStable.pipe(first(isStable => isStable === true));
+        const everySixHours$ = interval(2 * 60 * 60 * 1000);
+        const everySixHoursOnceAppIsStable$ = concat(appIsStable$, everySixHours$);
+
+        everySixHoursOnceAppIsStable$.subscribe(() => updates.checkForUpdate());
+    }
+
+    loadNewAppVersion() {
+        document.location.reload();
+    }
+}