Angular 5 - AuthGuard with

AuthGuard.ts

import { Injectable } from '@angular/core';
import {CanActivate, ActivatedRouteSnapshot, RouterStateSnapshot, Router} from '@angular/router';
import { Observable } from 'rxjs/Observable';
import {NbAuthService} from '@nebular/auth';
import { tap } from 'rxjs/operators/tap';
import 'rxjs/add/operator/mergeMap';
import {UsersDsService} from '../data-source/users-ds.service';

@Injectable()
export class AuthGuard implements CanActivate {
  constructor( private authService: NbAuthService, private router: Router,  private userDS: UsersDsService) {}
  canActivate(
    next: ActivatedRouteSnapshot,
    state: RouterStateSnapshot): Observable<boolean> | Promise<boolean> | boolean {
    return this.authService.isAuthenticated()
      .pipe(
        tap(authenticated => {
          if (!authenticated) {
            this.router.navigate(['auth/login']);
          } else {
            this.userDS.getRole().subscribe(role => {
              switch (role) {
                case 'admin': this.redirectIfNotInTheSamePage(next.routeConfig.path,
                  'pages/dashboard-page', 'dashboard-page'); break;
                case 'donor': this.redirectIfNotInTheSamePage(next.routeConfig.path,
                  'pages/donor-dashboard', 'donor-dashboard'); break;
                case 'parent': this.redirectIfNotInTheSamePage(next.routeConfig.path,
                  'pages/parent-dashboard', 'parent-dashboard'); break;
                case 'partner': this.redirectIfNotInTheSamePage(next.routeConfig.path,
                  'pages/partner-dashboard', 'partner-dashboard'); break;
                case 'student': this.redirectIfNotInTheSamePage(next.routeConfig.path,
                  'pages/student-dashboard', 'student-dashboard'); break;
              }
            });
          }
        }),
    );
  }
  private redirectIfNotInTheSamePage(iWantGoTo: string, allowedFullPath: string, allowedPath: string) {
    (iWantGoTo !== allowedPath) ? this.router.navigate([allowedFullPath]) : '';
  }
}