Fake Backend API - DL Angular 6 - 2019

import { HttpEvent, HttpHandler, HttpInterceptor, HttpRequest, HttpResponse } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { Observable, of, throwError } from 'rxjs';
import { delay, dematerialize, materialize, mergeMap } from 'rxjs/operators';
import { environment } from '../../../environments/environment';


// Based on http://jasonwatmore.com/post/2018/06/22/angular-6-mock-backend-example-for-backendless-development


@Injectable({
  providedIn: 'root'
})
export class FakeBackendApiInterceptor implements HttpInterceptor {

  constructor() { }

  intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {

    // array in local storage for registered users
    let users: any[] = JSON.parse(localStorage.getItem('users')) || [];

    // array in local storage for registered events
    let allEvents: any[] = JSON.parse(localStorage.getItem('events')) || {};
    let events: any[] = [];



    // add a dummy user with some dummy events
    users[0] = {
      id: 1,
      username: 'dummy',
      password: 'dummy'
    };
    localStorage.setItem('users', JSON.stringify(users));

    allEvents['dummy'] = (allEvents && allEvents['dummy'] ? allEvents['dummy'] : []);
    allEvents['dummy'][0] = {
      id: 1,
      description: 'Some event in the future',
      date: new Date(2100, 12, 31),
    };
    allEvents['dummy'][1] = {
      id: 2,
      description: 'Some event in the past',
      date: new Date(1900, 12, 31),
    };
    localStorage.setItem('events', JSON.stringify(allEvents));


    // get authenticated user from token (if available)
    let username: string = ('' + request.headers.get('Authorization')).replace('Bearer ', '');
    let user: any = null;
    let filteredUsers = users.filter(user => { return user.username === username; });
    if (filteredUsers && filteredUsers.length) {
      user = filteredUsers[0];
      events = (allEvents && allEvents[username] ? allEvents[username] : []);
    }



    // wrap in delayed observable to simulate server api call
    return of(null).pipe(mergeMap(() => {





      // get current user
      if (request.url.includes(`${environment.API_BASE_URL}${environment.API_GetAuthenticatedUser}`) && request.method === 'GET') {
        // if there is a logged in user return 200 OK with user details and fake jwt token
        if (user) {
          let body = {
            ...user // Copy user details
          };
          return of(new HttpResponse({ status: 200, body: body }));
        } else {
          // return 401 not authorised if token is null or invalid
          return throwError({ error: { message: 'Unauthorised' } });
        }
      }



      // register user
      if (request.url.includes(`${environment.API_BASE_URL}${environment.API_Register}`) && request.method === 'PUT') {
        // get new user object from post body
        let newUser = request.body;

        // validation
        if (!newUser.username) {
          return throwError({ error: { message: 'Username cannot be empty' } });
        }
        let duplicateUser = users.filter(user => { return user.username === newUser.username; }).length;
        if (duplicateUser) {
          return throwError({ error: { message: 'Username "' + newUser.username + '" is already taken' } });
        }

        // save new user
        newUser.id = Object.keys(users).length + 1;
        users.push(newUser);
        localStorage.setItem('users', JSON.stringify(users));

        // respond 200 OK
        return of(new HttpResponse({ status: 200 }));
      }



      // login
      if (request.url.includes(`${environment.API_BASE_URL}${environment.API_Login}`) && request.method === 'POST') {
        // find if any user matches login credentials
        let filteredUsers = users.filter(user => {
          return user.username === request.body.username && user.password === request.body.password;
        });

        if (filteredUsers.length) {
          // if login details are valid return 200 OK with user details and fake jwt token
          let user = filteredUsers[0];
          let body = {
            id: user.id,
            username: user.username,
            token: user.username // We use the username as token to diferentiate which user is authenticated
          };

          return of(new HttpResponse({ status: 200, body: body }));
        } else {
          // else return 400 bad request
          return throwError({ error: { message: 'Username or password is incorrect' } });
        }
      }



      // logout
      if (request.url.includes(`${environment.API_BASE_URL}${environment.API_Logout}`) && request.method === 'POST') {
        // Always return success in this mock
        let body = {};
        return of(new HttpResponse({ status: 200, body: body }));
      }






      // get events
      if (request.url.includes(`${environment.API_BASE_URL}${environment.API_GetAllEvents}`) && request.method === 'GET') {
        if (user) {
          return of(new HttpResponse({ status: 200, body: events }));
        } else {
          // return 401 not authorised if token is null or invalid
          return throwError({ error: { message: 'Unauthorised' } });
        }
      }



      // create event
      if (request.url.includes(`${environment.API_BASE_URL}${environment.API_CreateEvent}`) && request.method === 'POST') {
        if (user) {

          // get new event object from post body
          let newEvent = request.body;

          // validation
          if (!newEvent.description) {
            return throwError({ error: { message: 'Description cannot be empty' } });
          }

          // save new event
          newEvent.id = Object.keys(allEvents).length + 1;
          events.push(newEvent);
          allEvents[username] = events;
          localStorage.setItem('events', JSON.stringify(allEvents));

          // respond 200 OK
          return of(new HttpResponse({ status: 200 }));

        } else {
          // return 401 not authorised if token is null or invalid
          return throwError({ error: { message: 'Unauthorised' } });
        }
      }







      // update event
      if (request.url.includes(`${environment.API_BASE_URL}${environment.API_UpdateEvent}`) && request.method === 'PUT') {
        if (user) {

          // get new event object from post body
          let changedEvent = request.body;

          // validation
          if (!changedEvent.id) {
            return throwError({ error: { message: 'Id cannot be empty' } });
          }
          if (!changedEvent.description) {
            return throwError({ error: { message: 'Description cannot be empty' } });
          }

          // find event by id in events array
          for (let i = 0; i < events.length; i++) {
            if (events[i].id === changedEvent.id) {
              // update event
              events[i] = changedEvent;
              allEvents[username] = events;
              localStorage.setItem('events', JSON.stringify(allEvents));
              break;
            }
          }

          // respond 200 OK
          return of(new HttpResponse({ status: 200 }));

        } else {
          // return 401 not authorised if token is null or invalid
          return throwError({ error: { message: 'Unauthorised' } });
        }
      }



      // remove event
      if (request.url.includes(`${environment.API_BASE_URL}${environment.API_RemoveEvent}`) && request.method === 'DELETE') {
        if (user) {
          // find event by id in events array
          let urlParts = request.url.split('/');
          let id = parseInt(urlParts[urlParts.length - 1]);
          for (let i = 0; i < events.length; i++) {
            let event = events[i];
            if (event.id === id) {
              // delete event
              events.splice(i, 1);
              allEvents[username] = events;
              localStorage.setItem('events', JSON.stringify(allEvents));
              break;
            }
          }

          // respond 200 OK
          return of(new HttpResponse({ status: 200 }));
        } else {
          // return 401 not authorised if token is null or invalid
          return throwError({ error: { message: 'Unauthorised' } });
        }
      }





      // pass through any requests not handled above
      return next.handle(request);

    }))

      // call materialize and dematerialize to ensure delay even if an error is thrown (https://github.com/Reactive-Extensions/RxJS/issues/648)
      .pipe(materialize())
      .pipe(delay(200))
      .pipe(dematerialize());
  }
}