users.service.ts

import { Injectable }from '@angular/core';
import { HttpClient, HttpHeaders }from '@angular/common/http';

import { Observable } from 'rxjs/Observable';
import { catchError, tap } from 'rxjs/operators';
import {User} from './user';
import {of} from "rxjs/observable/of";

const httpOptions = { headers: new HttpHeaders({ 'Content-Type': 'application/json' })};

@Injectable()
export class UsersService {

  private usersUrl: string = '/api/users';
  constructor (private http: HttpClient) {}

  getUsers(): Observable<User[]> {
    return this.http.get<User[]>(this.usersUrl)
      .pipe(
        tap(heroes => this.log(`fetched users`)),
        catchError(this.handleError('getUsers', []))
      );
  }

  getUser(id: number): Observable<User> {
    const url = `${this.usersUrl}/${id}`;
    return this.http.get<User>(url).pipe(
      tap(_ => this.log(`fetched hero id=${id}`)),
      catchError(this.handleError<User>(`getUser id=${id}`))
    );
  }

  addUser (user: User): Observable<User> {
    return this.http.post<User>(this.usersUrl, user, httpOptions).pipe(
      tap((user: User) => this.log(`added User w/ id=${user.id}`)),
      catchError(this.handleError<User>('addUser'))
    );
  }

  deleteUser (id: string): Observable<User> {
    const url = `${this.usersUrl}/${id}`;

    return this.http.delete<User>(url, httpOptions).pipe(
      tap(_ => this.log(`deleted user id=${id}`)),
      catchError(this.handleError<User>('deleteUser'))
    );
  }

  updateUser (user: User): Observable<null> {
    return this.http.put(this.usersUrl, user, httpOptions).pipe(
      tap(_ => this.log(`updated user id=${user.id}`)),
      catchError(this.handleError<any>('updateUser'))
    );
  }

  private handleError<T> (operation = 'operation', result?: T) {
    return (error: any): Observable<T> => {
      console.error(error);
      return of(result as T);
    };
  }

  private log(message: string) {
    console.log('UserService: ' + message);
  }
}