System Architecture

// Example API endpoint structure
app.get("/api/users/:id", authenticate, async (req, res) => {
    const user = await userService.find(req.params.id);
    res.json(user);
});

class UserService {
    async find(id: string): Promise<User> {
        // Validation
        if (!id) throw new ValidationError("ID required");

        // Database query
        const user = await db.users.findOne({ id });

        // Error handling
        if (!user) throw new NotFoundError("User not found");

        return user;
    }
}

interface UserRepository {
    find(id: string): Promise<User | null>;
    save(user: User): Promise<void>;
    delete(id: string): Promise<void>;
}

const container = {
    userRepository: new PostgresUserRepository(db),
    userService: new UserService(container.userRepository),
    authService: new AuthService(container.userService),
};

// JWT token generation
const token = jwt.sign(
    {
        userId: user.id,
        email: user.email,
    },
    process.env.JWT_SECRET,
    { expiresIn: "7d" }
);

const authorize = (roles: string[]) => {
    return (req, res, next) => {
        if (!roles.includes(req.user.role)) {
            return res.status(403).json({ error: "Forbidden" });
        }
        next();
    };
};

app.delete("/api/users/:id", authorize(["admin"]), deleteUser);

logger.info("User created", {
    correlationId: req.id,
    userId: user.id,
    timestamp: Date.now(),
});