/design-patterns [analysis_target] [options]

# Analyze patterns for entire project
/design-patterns
 
# Suggest patterns for specific file
/design-patterns src/services/user.js --suggest
 
# Check SOLID principles
/design-patterns --solid
 
# Detect anti-patterns
/design-patterns --anti-patterns

S - Single Responsibility (one class, one job)
O - Open/Closed (open for extension, closed for modification)
L - Liskov Substitution (subtypes should be replaceable)
I - Interface Segregation (don't force unused methods)
D - Dependency Inversion (depend on abstractions, not details)

Design Pattern Analysis Report
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
 
Currently Used Patterns
├─ Observer Pattern: EventEmitter (12 instances)
├─ Factory Pattern: UserFactory (3 instances)
├─ Singleton Pattern: DatabaseConnection (1 instance)
└─ Strategy Pattern: PaymentProcessor (5 instances)
 
Recommended Patterns
├─ [HIGH] Repository Pattern
│  └─ Where: src/models/*.js
│  └─ Why: Separate data access from business logic
│  └─ Example:
│      class UserRepository {
│        async findById(id) { ... }
│        async save(user) { ... }
│      }
│
├─ [MED] Command Pattern
│  └─ Where: src/api/handlers/*.js
│  └─ Why: Standardize how requests are handled
│
└─ [LOW] Decorator Pattern
   └─ Where: src/middleware/*.js
   └─ Why: Better way to combine features
 
SOLID Violations Found
├─ [S] UserService: Does too much (auth AND authorization)
├─ [O] PaymentGateway: Must change code to add payment types
├─ [D] EmailService: Depends on specific classes, not interfaces
└─ [I] IDataStore: Has methods nobody uses
 
How to Fix
1. Split UserService into AuthService and AuthorizationService
2. Add a PaymentStrategy interface for new payment types
3. Create an EmailService interface
4. Break up IDataStore into smaller interfaces

# See what happens if you use a pattern
/design-patterns --impact-analysis Repository
 
# Get example code for a pattern
/design-patterns --generate Factory --for src/models/Product.js
 
# Find patterns that work well together
/design-patterns --combine --context "API with caching"
 
# Check your architecture
/design-patterns --architecture MVC

class OrderService {
  processOrder(order, paymentType) {
    if (paymentType === "credit") {
      // Credit card processing
    } else if (paymentType === "paypal") {
      // PayPal processing
    }
    // Other payment methods...
  }
}

// Strategy interface
class PaymentStrategy {
  process(amount) {
    throw new Error("Must implement process method");
  }
}
// Concrete strategies
class CreditCardPayment extends PaymentStrategy {
  process(amount) {
    /* Implementation */
  }
}
// Context
class OrderService {
  constructor(paymentStrategy) {
    this.paymentStrategy = paymentStrategy;
  }
  processOrder(order) {
    this.paymentStrategy.process(order.total);
  }
}