Bug fix for #77 (#91)

* Bug fix for #77
- Users will now be warned if their tokens are about to expire
- Users will be logged out upon token expiration

* Update from toast to alert for expired token

* Replace interval with timer

* Enhance warning

* Fix linting

* Fix takeUntilDestroyed

https://stackoverflow.com/questions/76264067/takeuntildestroyed-can-only-be-used-within-an-injection-context

---------

Co-authored-by: Samuel Lim <[email protected]>

frontend/src/_services/authentication.service.ts

@@ -1,23 +1,28 @@
 // Modified from https://jasonwatmore.com/post/2022/11/15/angular-14-jwt-authentication-example-tutorial#login-component-ts
-import { Injectable } from '@angular/core';
+import { DestroyRef, inject, Injectable } from '@angular/core';
 import { Router } from '@angular/router';
 import { HttpClient } from '@angular/common/http';
-import { BehaviorSubject, Observable } from 'rxjs';
+import { BehaviorSubject, Observable, timer } from 'rxjs';
+import { takeUntilDestroyed } from '@angular/core/rxjs-interop';
 import { map, switchMap } from 'rxjs/operators';
 import { UServRes } from '../_models/user.service.model';
 import { User } from '../_models/user.model';
 import { ApiService } from './api.service';
+import { ToastService } from './toast.service';
 
 @Injectable({ providedIn: 'root' })
 export class AuthenticationService extends ApiService {
     protected apiPath = 'user';
 
+    private destroyRef = inject(DestroyRef);
+
     private userSubject: BehaviorSubject<User | null>;
     public user$: Observable<User | null>;
 
     constructor(
         private router: Router,
         private http: HttpClient,
+        private toastService: ToastService,
     ) {
         super();
         const userData = localStorage.getItem('user');
@@ -53,6 +58,8 @@ export class AuthenticationService extends ApiService {
                     }
                     localStorage.setItem('user', JSON.stringify(user));
                     this.userSubject.next(user);
+                    this.startTokenExpiryCheck();
+
                     return user;
                 }),
             );
@@ -119,4 +126,41 @@ export class AuthenticationService extends ApiService {
             }),
         );
     }
+
+    displaySessionExpiryWarning(): void {
+        this.toastService.showToast('Your session will expire in less than 5 minutes. Please log in again.');
+    }
+
+    public startTokenExpiryCheck(): void {
+        const tokenExpirationTime = this.getTokenExpiration();
+        if (!tokenExpirationTime) {
+            this.logout();
+            return;
+        }
+
+        const oneMinute = 60 * 1000;
+        const timeLeft = tokenExpirationTime - Date.now();
+        if (timeLeft > 5 * oneMinute) {
+            timer(timeLeft - 5 * oneMinute)
+                .pipe(takeUntilDestroyed(this.destroyRef))
+                .subscribe(() => this.displaySessionExpiryWarning());
+        } else {
+            this.displaySessionExpiryWarning();
+        }
+
+        timer(timeLeft)
+            .pipe(takeUntilDestroyed(this.destroyRef))
+            .subscribe(() => {
+                alert('Your session has expired. Please log in again.');
+                this.logout();
+            });
+    }
+
+    private getTokenExpiration() {
+        const user = this.userValue;
+        if (!user || !user.accessToken) return null;
+
+        const tokenPayload = JSON.parse(atob(user.accessToken.split('.')[1]));
+        return tokenPayload.exp ? tokenPayload.exp * 1000 : null;
+    }
 }

frontend/src/app/app.component.html

@@ -1,4 +1,5 @@
 <main>
     <app-navigation-bar />
+    <p-toast></p-toast>
     <router-outlet />
 </main>

frontend/src/app/app.component.ts

@@ -1,16 +1,24 @@
-import { Component } from '@angular/core';
+import { Component, OnInit } from '@angular/core';
 import { RouterOutlet } from '@angular/router';
 import { ButtonModule } from 'primeng/button';
 import { PasswordModule } from 'primeng/password';
+import { ToastModule } from 'primeng/toast';
 import { NavigationBarComponent } from './navigation-bar/navigation-bar.component';
-
+import { AuthenticationService } from '../_services/authentication.service';
+import { MessageService } from 'primeng/api';
 @Component({
     selector: 'app-root',
     standalone: true,
-    imports: [NavigationBarComponent, RouterOutlet, ButtonModule, PasswordModule],
+    imports: [NavigationBarComponent, RouterOutlet, ButtonModule, PasswordModule, ToastModule],
+    providers: [MessageService],
     templateUrl: './app.component.html',
     styleUrl: './app.component.css',
 })
-export class AppComponent {
+export class AppComponent implements OnInit {
     title = 'frontend';
+
+    constructor(private authService: AuthenticationService) {}
+    ngOnInit() {
+        this.authService.startTokenExpiryCheck();
+    }
 }