DDD Refactoring Guide

# DDD Refactoring Guide

## Refactoring Strategy

### 1. Domain Layer Refactoring
- Extract business rules from services into domain entities
- Create value objects for complex data types
- Implement domain services for business logic that doesn't belong to entities
- Define clear aggregate boundaries

### 2. Application Layer Refactoring
- Move orchestration logic to use cases
- Remove business logic from controllers/components
- Implement command/query separation
- Add proper transaction boundaries

### 3. Infrastructure Layer Refactoring
- Abstract external dependencies behind interfaces
- Implement repository pattern for data access
- Create adapters for third-party services
- Handle configuration and environment concerns

### 4. Presentation Layer Refactoring
- Remove business logic from components
- Implement proper state management
- Use DTOs for data transfer
- Handle user interaction concerns only

## Refactoring Steps
1. **Identify Violations**: Find code that violates DDD principles
2. **Extract Domain Logic**: Move business rules to domain layer
3. **Create Abstractions**: Define interfaces for external dependencies
4. **Implement Use Cases**: Create application services for workflows
5. **Update Components**: Clean up presentation layer
6. **Add Tests**: Ensure refactored code is well-tested

## Common Refactoring Patterns
- **Extract Domain Service**: Move business logic from application services
- **Create Value Objects**: Replace primitive types with meaningful objects
- **Implement Repository**: Abstract data access behind interfaces
- **Use Dependency Injection**: Inject dependencies rather than creating them
- **Separate Commands from Queries**: Implement CQRS pattern

## Validation After Refactoring
- All tests still pass
- No new circular dependencies
- Clear separation of concerns
- Improved testability
- Better maintainability

Refactor incrementally and validate each step to ensure code quality is maintained.