# System Patterns

## Architectural Patterns

### MVT Implementation
1. Models
   - Use abstract base classes for common fields
   - Implement custom model managers for complex queries
   - Define clear relationships and constraints
   - Include field-level validation

2. Views
   - Prefer class-based views
   - Use mixins for shared functionality
   - Implement proper permission checks
   - Handle HTMX requests explicitly

3. Templates
   - Maintain hierarchy with base templates
   - Use partial templates for HTMX responses
   - Implement component-based structure
   - Follow progressive enhancement

## Version Control Patterns

### Change Management
1. Batch Processing
   ```python
   class BatchChangeProcessor:
       def process_changes(self, changes, chunk_size=100):
           """Process changes in efficient batches"""
           with transaction.atomic():
               for chunk in chunked_queryset(changes, chunk_size):
                   self._process_chunk(chunk)
   ```

2. Caching Strategy
   ```python
   class VersionCache:
       def cache_history(self, instance):
           """Cache version history with TTL"""
           key = f"version_history_{instance.pk}"
           if not cache.get(key):
               history = instance.get_history()
               cache.set(key, history, timeout=3600)
   ```

3. Change Tracking
   ```python
   class ChangeTracker:
       def track_changes(self, instance):
           """Track changes with metadata"""
           return {
               'changes': self._diff_changes(instance),
               'metadata': self._collect_metadata(),
               'performance': self._get_metrics()
           }
   ```

### Performance Optimization

1. Query Patterns
   ```python
   class HistoryQuerySet:
       def optimized_history(self):
           """Optimized history query"""
           return self.select_related('branch')\
                     .prefetch_related('changes')\
                     .defer('large_fields')
   ```

2. Async Operations
   ```python
   class AsyncVersionControl:
       async def process_large_changes(self):
           """Handle large changes asynchronously"""
           async with atomic():
               # Async processing logic
   ```

3. Archiving Strategy
   ```python
   class HistoryArchiver:
       def archive_old_versions(self, age_days=90):
           """Archive old version history"""
           threshold = timezone.now() - timedelta(days=age_days)
           return self._move_to_archive(threshold)
   ```

## Design Patterns

### Data Access
1. Query Patterns
   - Use select_related() for foreign keys
   - Implement prefetch_related() for reverse relationships
   - Create custom model managers
   - Optimize database queries

2. Caching Strategy
   - Cache template fragments
   - Implement model-level caching
   - Use Redis for session storage
   - Cache invalidation rules
   - Version history caching
   - Differential caching for changes

### Frontend Patterns

1. HTMX Integration
   ```html
   <!-- Partial Update Pattern -->
   <div hx-get="/endpoint"
        hx-trigger="event"
        hx-target="#target">
   ```

2. AlpineJS Components
   ```html
   <!-- State Management Pattern -->
   <div x-data="{ state: {} }"
        x-init="state = await fetchData()">
   ```

3. Tailwind Components
   ```html
   <!-- Component Structure -->
   <div class="component-wrapper">
     <div class="component-header"></div>
     <div class="component-content"></div>
   </div>
   ```

## Version Control UI Patterns

1. Change Visualization
   ```html
   <!-- Diff View Pattern -->
   <div class="diff-view"
        x-data="diffViewer"
        x-init="loadDiff()">
     <div class="diff-header"></div>
     <div class="diff-content"></div>
   </div>
   ```

2. Branch Management
   ```html
   <!-- Branch Selector Pattern -->
   <div class="branch-selector"
        x-data="branchManager"
        @branch-changed="updateContent()">
   ```

3. Merge Resolution
   ```html
   <!-- Conflict Resolution Pattern -->
   <div class="conflict-resolver"
        x-data="conflictResolver"
        @resolve="handleResolution()">
   ```

## Authentication Patterns

### User Management
1. Custom User Model
   - Extended user profiles
   - Role-based permissions
   - Activity tracking
   - Profile customization

2. Authentication Flow
   - Login/registration process
   - Password reset workflow
   - Email verification
   - Session management

## Content Management

### Moderation Flow
1. Submission Process
   - Content validation
   - Automatic checks
   - Manual review queue
   - Approval workflow

2. Review System
   - Rating framework
   - Media handling
   - User verification
   - Content filtering

## Error Handling

### Backend Errors
1. Exception Handling
   ```python
   try:
       # Operation
   except SpecificException as e:
       # Specific handling
   except Exception as e:
       # Generic handling
   ```

2. Response Patterns
   ```python
   # Success Response
   return JsonResponse({'status': 'success', 'data': data})
   
   # Error Response
   return JsonResponse({'status': 'error', 'message': str(e)})
   ```

### Frontend Errors
1. User Feedback
   - Toast notifications
   - Inline validation
   - Form feedback
   - Error states

## Testing Patterns

### Performance Testing
```python
class VersionControlPerformanceTests(TestCase):
    def setUp(self):
        self.large_dataset = self.create_test_data()
        
    def test_batch_processing_performance(self):
        start_time = time.time()
        self.processor.process_changes(self.large_dataset)
        duration = time.time() - start_time
        self.assertLess(duration, self.acceptable_threshold)
```

### Scale Testing
```python
class ScaleTestCase(TestCase):
    def test_version_history_scaling(self):
        with self.assertNumQueries(1):  # Ensure efficient querying
            self.repository.get_history()
```

### Integration Tests
```python
class ViewTests(TestCase):
    def setUp(self):
        self.client = Client()
        
    def test_view_functionality(self):
        # Test implementation
```

## Development Workflows

### Feature Development
1. Planning
   - Technical specification
   - Component design
   - Database schema
   - API endpoints

2. Implementation
   - Model creation
   - View implementation
   - Template design
   - Testing coverage

3. Review Process
   - Code review
   - Testing verification
   - Documentation update
   - Deployment planning
   
4. Performance Review
   - Query analysis
   - Cache efficiency
   - Load testing
   - Scalability verification