Backend Class Design

The Backend is built using modern C++23 and the Crow framework. It follows a layered MVC-like architecture (Controller-Model-Service).

Description

This document visualizes the class structure and relationships of the Cake Planner Backend.

Class Diagrams

The following diagram illustrates the core classes and their relationships. To ensure readability, the classes are arranged in logical tiers.

Class Diagram

Component Details

The application follows a defined Model-View-Controller (MVC) pattern (where "View" is JSON serialization).

Controllers

Controllers handle incoming HTTP requests, parse JSON bodies, and delegate logic to Models or Services. They are the entry point for the REST API.

• AuthController: Handles Registration, Login, Password Reset, and 2FA setup.
• UserController: Manages user profiles, settings (language), and self-deletion.
• EventController: Handles event creation, listing, deletion, rating, and photo uploads.
• AdminController: Provides endpoints for user and group management (Admin only).
• SystemController: Exposes system health and version information.

Models

Models represent the data entities and encompass the business logic and database interactions.

• User: Represents a registered user. Handles authentication checks, password hashing, and group membership logic.
• Event: Represents a cake event. Handles creation rules, date filtering, and rating calculations.
• ConfigModel: Loads and provides access to application configuration (env vars).

Services

Services encapsulate business logic that spans multiple models or involves external communication.

• NotificationService: Abstraction layer for sending business-level emails (e.g., "New Cake Alert"). localized in German/English.
• SmtpService: Low-level wrapper around the SMTP library to send raw emails asynchronously via Qt's event loop.

Middleware

• AuthMiddleware: Intercepts every request (except login/register) to validate the JWT Bearer Token. It populates the request context with the authenticated user's ID and role.

Utilities & Core

Helper classes for common tasks.

• DatabaseManager: Singleton that manages the SQLite connection pool and handles schema migrations.
• TokenUtils: Generates and verifies JWTs (JSON Web Tokens).
• PasswordUtils: Handles secure password hashing using Argon2id.
• ImageProcessor: Resizes uploaded images and converts them to WebP format.