Core Module – Low Level Design

⚙️ Step 8: Core Module – Low Level Design (LLD)

This document describes the core module that provides app-wide singleton services, route guards, HTTP interceptors, and global utilities.

📦 Module Structure

src/
├── app/
│   └── core/
│       ├── services/
│       │   ├── auth.service.ts
│       │   ├── token.service.ts
│       │   ├── logger.service.ts
│       │   └── error-handler.service.ts
│       ├── guards/
│       │   └── auth.guard.ts
│       ├── interceptors/
│       │   ├── auth.interceptor.ts
│       │   └── error.interceptor.ts
│       ├── core.module.ts

🧱 Service Breakdown

🔐 AuthService

• Handles authentication logic: login, logout, token refresh
• Stores JWT tokens securely via TokenService
• Provides current user info and authentication status

🔑 TokenService

• Manages storing and retrieving JWT tokens from localStorage or sessionStorage
• Provides token expiration checks and refresh triggers

📝 LoggerService

• Centralized logging for debugging and error tracking
• Supports different log levels (info, warn, error)
• Could integrate with external logging services

🚨 ErrorHandlerService

• Global error handler capturing uncaught exceptions
• Displays user-friendly error messages or redirects
• Reports errors to external monitoring (optional)

🚦 Guards

AuthGuard

• Protects routes that require authentication
• Redirects unauthenticated users to login page

@Injectable({ providedIn: "root" })
export class AuthGuard implements CanActivate {
  constructor(private authService: AuthService, private router: Router) {}

  canActivate(): boolean {
    if (this.authService.isLoggedIn()) {
      return true;
    }
    this.router.navigate(["/login"]);
    return false;
  }
}

🛡️ Interceptors

AuthInterceptor

• Attaches JWT token to outgoing HTTP requests' Authorization header

ErrorInterceptor

• Intercepts HTTP errors globally
• Handles common status codes (401, 403, 500) with proper user notifications or logout

📐 Module Definition

@NgModule({
  providers: [
    AuthService,
    TokenService,
    LoggerService,
    ErrorHandlerService,
    AuthGuard,
    {
      provide: HTTP_INTERCEPTORS,
      useClass: AuthInterceptor,
      multi: true,
    },
    {
      provide: HTTP_INTERCEPTORS,
      useClass: ErrorInterceptor,
      multi: true,
    },
  ],
})
export class CoreModule {}

✅ Responsibilities Summary