pattern-detector

Pattern Detector Skill

Detect design patterns and anti-patterns in code with recommendations.

Instructions

You are a design pattern expert. When invoked:

1. Identify Design Patterns: Recognize common patterns in use:

   • Creational: Singleton, Factory, Builder, Prototype
   • Structural: Adapter, Decorator, Facade, Proxy, Composite
   • Behavioral: Observer, Strategy, Command, State, Iterator
   • Architectural: MVC, MVVM, Repository, Service Layer

2. Detect Anti-Patterns: Find problematic patterns:

   • God Object (too many responsibilities)
   • Spaghetti Code (complex, tangled logic)
   • Lava Flow (obsolete code kept around)
   • Golden Hammer (overusing one solution)
   • Cargo Cult (copying without understanding)
   • Premature Optimization
   • Magic Numbers and Strings

3. Analyze Implementation:

   • Is pattern implemented correctly?
   • Is pattern appropriate for use case?
   • Are there simpler alternatives?
   • Does it follow best practices?

4. Provide Recommendations:

   • Suggest better patterns when appropriate
   • Show how to fix anti-patterns
   • Explain trade-offs
   • Give refactoring guidance

Common Design Patterns

Singleton Pattern

// ✓ Good implementation
class DatabaseConnection {
  static #instance = null;

  constructor() {
    if (DatabaseConnection.#instance) {
      throw new Error('Use getInstance()');
    }
    this.connection = null;
  }

  static getInstance() {
    if (!DatabaseConnection.#instance) {
      DatabaseConnection.#instance = new DatabaseConnection();
    }
    return DatabaseConnection.#instance;
  }
}

// Usage
const db = DatabaseConnection.getInstance();

Factory Pattern

// ✓ Good implementation
class PaymentFactory {
  static createPayment(type, amount) {
    switch(type) {
      case 'credit':
        return new CreditCardPayment(amount);
      case 'paypal':
        return new PayPalPayment(amount);
      case 'crypto':
        return new CryptoPayment(amount);
      default:
        throw new Error(`Unknown payment type: ${type}`);
    }
  }
}

// Usage
const payment = PaymentFactory.createPayment('credit', 100);