added fake-backend for login and registration testing

src/app/utils/fake-backend.spec.ts

@@ -0,0 +1,7 @@
+import { FakeBackend } from './fake-backend';
+
+describe('FakeBackend', () => {
+  it('should create an instance', () => {
+    expect(new FakeBackend()).toBeTruthy();
+  });
+});

src/app/utils/fake-backend.ts

@@ -0,0 +1,73 @@
+import { Injectable } from '@angular/core';
+import { HttpRequest, HttpResponse, HttpHandler, HttpEvent, HttpInterceptor, HTTP_INTERCEPTORS } from '@angular/common/http';
+import { Observable, of, throwError } from 'rxjs';
+import { delay, mergeMap, materialize, dematerialize } from 'rxjs/operators';
+
+
+let users = JSON.parse(localStorage.getItem('users')) || [];
+
+@Injectable()
+export class FakeBackend implements HttpInterceptor {
+  intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
+    const { url, method, headers, body } = request;
+
+    return of(null)
+      .pipe(mergeMap(handleRoute))
+      .pipe(materialize())
+      .pipe(delay(500))
+      .pipe(dematerialize());
+
+    function handleRoute() {
+      switch (true) {
+        case url.endsWith('fake_login') && method === 'POST':
+          return authenticate();
+        case url.endsWith('fake_registration') && method === 'POST':
+          return register();
+        default:
+          return next.handle(request);
+      }
+    }
+
+    function authenticate() {
+      const { username, password } = body;
+      const user = users.find(x => x.username === username.value && x.password === password.value);
+      if (!user) {
+        console.log(password);
+        return error('Username or password is incorrect.');
+      }
+      return ok({
+        id: user.id,
+        username: user.username,
+        token: 'fake-jwt-token',
+      });
+    }
+
+    function register() {
+      const user = body;
+
+      if (users.find(x => x.username === user.username)) {
+        return error('Username ' + user.username + ' is already taken.');
+      }
+
+      user.id = users.length ? Math.max(...users.map(x => x.id)) + 1 : 1;
+      users.push(user);
+      localStorage.setItem('users', JSON.stringify(users));
+      console.log('Register user: ' + user);
+      return ok();
+    }
+
+    function ok(body?) {
+      return of(new HttpResponse({ status: 200, body }));
+    }
+
+    function error(message) {
+      return throwError({ error: { message } });
+    }
+  }
+}
+
+export const fakeBackendProvider = {
+  provide: HTTP_INTERCEPTORS,
+  useClass: FakeBackend,
+  multi: true,
+}