7. HttpClient, interceptors and error handling

// app.config.ts
export const appConfig: ApplicationConfig = {
  providers: [
    provideRouter(routes, withComponentInputBinding()),
    provideHttpClient(withInterceptors([authInterceptor, errorInterceptor])),
  ],
};

export const authInterceptor: HttpInterceptorFn = (req, next) => {
  const token = inject(AuthService).token();
  return next(token ? req.clone({ setHeaders: { Authorization: `Bearer ${token}` } }) : req);
};

export const errorInterceptor: HttpInterceptorFn = (req, next) =>
  next(req).pipe(
    retry({ count: 2, delay: 500 }),                          // only for idempotent GETs in practice
    catchError((err: HttpErrorResponse) => {
      if (err.status === 401) inject(Router).navigate(["/login"]);
      return throwError(() => err);
    }),
  );

// In a service
getOrder(id: number) {
  return this.http.get<Order>(`/api/orders/${id}`, { params: { include: "lines" } });
}