add http interceptor

src/app/services/logging-interceptor.service.ts

@@ -0,0 +1,50 @@
+import { HttpHandler, HttpRequest, HttpResponse } from '@angular/common/http';
+import { Injectable } from '@angular/core';
+import { finalize, tap } from 'rxjs/operators';
+import { BackgroundService } from './background.service';
+
+@Injectable({
+  providedIn: 'root'
+})
+export class LoggingInterceptorService {
+
+  constructor(
+    private backgroundservice: BackgroundService,
+  ) {}
+
+  intercept(req: HttpRequest<any>, next: HttpHandler) {
+    const started = Date.now();
+    let ok: string;
+
+    // extend server response observable with logging
+    return next.handle(req)
+      .pipe(
+        tap({
+          // Succeeds when there is a response; ignore other events
+          next: (event) => {
+
+            ok = event instanceof HttpResponse ? 'succeeded' : ''
+            
+            if(ok == 'succeeded' || (typeof event['status'] == 'number' && event['status'] !=0)) {
+              // set to online
+              this.backgroundservice.online();
+            }
+            
+          },
+          // Operation failed; error is an HttpErrorResponse
+          error: (error) => {
+            if (error.status === 0 && error.error instanceof ProgressEvent && !req.url.includes('UserAuthentication/Login')) {
+              // A client-side or network error occurred. Handle it accordingly.
+              this.backgroundservice.offline();
+            }
+          }
+        }),
+        // Log when response observable either completes or errors
+        finalize(() => {
+          // const elapsed = Date.now() - started;
+          // const msg = `${req.method} "${req.urlWithParams}"
+          //    ${ok} in ${elapsed} ms.`;
+        })
+      );
+  }
+}