atelier/examples/bad/god-object.md

# Bad Example: God Object

> A component that violates Atelier principles. Each violation is cited.

## The Code

```typescript
// UserManager.ts — 1,200 lines
class UserManager {
  private users: User[] = [];
  private cache: Map<string, User> = new Map();
  private db: Database;
  private emailService: EmailService;
  private logger: Logger;
  private auditLog: AuditLog;

  constructor(db: Database, email: EmailService, logger: Logger, audit: AuditLog) {
    this.db = db;
    this.emailService = email;
    this.logger = logger;
    this.auditLog = audit;
  }

  // CRUD
  async createUser(data: UserData): Promise<User> { /* 80 lines */ }
  async getUser(id: string): Promise<User> { /* 40 lines */ }
  async updateUser(id: string, data: Partial<UserData>): Promise<User> { /* 60 lines */ }
  async deleteUser(id: string): Promise<void> { /* 50 lines */ }
  async listUsers(page: number): Promise<User[]> { /* 40 lines */ }

  // Email
  async sendWelcomeEmail(user: User): Promise<void> { /* 50 lines */ }
  async sendPasswordReset(user: User): Promise<void> { /* 50 lines */ }
  async sendDeletionNotice(user: User): Promise<void> { /* 40 lines */ }

  // Auth
  async authenticate(email: string, password: string): Promise<boolean> { /* 70 lines */ }
  async authorize(userId: string, action: string): Promise<boolean> { /* 60 lines */ }
  async hashPassword(password: string): Promise<string> { /* 20 lines */ }

  // Cache
  private cacheGet(id: string): User | null { /* 20 lines */ }
  private cacheSet(user: User): void { /* 20 lines */ }
  private cacheInvalidate(id: string): void { /* 20 lines */ }

  // Audit
  private logAudit(action: string, userId: string): void { /* 30 lines */ }

  // Validation
  private validateEmail(email: string): boolean { /* 20 lines */ }
  private validatePassword(password: string): boolean { /* 20 lines */ }

  // Serialization
  toJSON(user: User): Record<string, unknown> { /* 30 lines */ }
  fromJSON(data: Record<string, unknown>): User { /* 30 lines */ }

  // ... 200 more lines of helper methods
}
```

## Violations

### C3 Simplicity (Core)
- A 1,200-line class doing 8 different things (CRUD, email, auth, cache, audit, validation, serialization).
- The class cannot be understood in one read. Complexity is the liability.
- **Fix:** Split into `UserRepository` (CRUD), `UserEmailService` (email), `UserAuthService` (auth), `UserCache` (cache), `UserAuditLogger` (audit), `UserValidator` (validation), `UserSerializer` (serialization).

### C6 Composability (Core)
- The class takes 4 dependencies and does 8 jobs. It is not composable; it is monolithic.
- You cannot reuse the email logic without the DB, the cache, the audit log.
- **Fix:** Each responsibility is its own class. Compose them: `UserEmailService` takes only `EmailService`.

### components.md §1 Single Responsibility (UI/UX, applies to code)
- The class name is `UserManager`. "Manager" is a smell — it manages what? Everything.
- If the name is "Manager," it has no single responsibility.
- **Fix:** Name by responsibility: `UserRepository`, `UserAuthService`. Names that cannot be "And"-ed.

### C4 Locality (Core)
- Cache logic is in the same class as email logic. A change to cache touches the email methods' neighbor.
- Related logic (cache get/set/invalidate) is grouped, but unrelated logic (email) is adjacent.
- **Fix:** `UserCache` is its own class. Cache changes are local to cache.

### C2 Clarity (Core)
- A reader cannot answer "what does `UserManager` do?" in one sentence.
- The class has 20+ methods. The reader must scan all of them to find the one they need.
- **Fix:** Smaller classes with clear names. The name is the documentation.

### Security P2 Least Privilege (Security)
- The class has `db`, `emailService`, `logger`, `auditLog` — all available to all methods.
- `sendWelcomeEmail` has access to `db.delete`. Least privilege is violated.
- **Fix:** Each service has only the dependencies it needs. `UserEmailService` has `EmailService`, not `Database`.

### Testing P2 Independence (Testing)
- To test `sendWelcomeEmail`, you must construct `UserManager` with a real/mock DB, email, logger, audit.
- The test setup is 4 mocks for one method. Independence is violated.
- **Fix:** Test `UserEmailService` with one mock (`EmailService`).

## What This Example Reveals

The "God Object" is the cardinal sin of OOP. It violates C3 (Simplicity), C6 (Composability), C4 (Locality), and C2 (Clarity) simultaneously. Every other principle suffers downstream:

- Testing is hard (T2 Independence).
- Security is loose (S2 Least Privilege).
- Evolution is brittle (a change to email risks cache).
- Review is exhausting (a 1,200-line diff).

The fix is always the same: **decompose by responsibility**. The class name is the test: if it is "Manager," "Handler," or "Helper," it has no single responsibility.