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+# Code Refactoring Summary
+
+This document summarizes the refactoring changes made to the lsfg-vk plugin based on the code review.
+
+## 🏗️ File Structure Changes
+
+### Before (Single File)
+```
+main.py (500+ lines)
+├── InstallationService
+├── DllDetectionService  
+├── ConfigurationService
+└── Plugin
+```
+
+### After (Modular Package)
+```
+lsfg_vk/
+├── __init__.py           # Package exports
+├── constants.py          # All constants and configuration
+├── types.py             # TypedDict definitions for responses
+├── base_service.py      # Common functionality for all services
+├── installation.py      # InstallationService
+├── dll_detection.py     # DllDetectionService
+├── configuration.py     # ConfigurationService
+└── plugin.py            # Main Plugin class
+
+tests/
+├── conftest.py          # Test configuration and fixtures
+├── test_installation.py # Tests for InstallationService
+├── test_configuration.py # Tests for ConfigurationService
+└── test_dll_detection.py # Tests for DllDetectionService
+
+main.py                  # Simple import/export for Decky compatibility
+requirements-test.txt    # Testing dependencies
+```
+
+## ✨ Key Improvements Implemented
+
+### 1. **Single Responsibility & Modularity**
+- Split monolithic file into focused modules
+- Each service handles one concern
+- Easier to navigate and maintain
+- Reduced merge conflicts
+
+### 2. **Constants Management**
+- All hardcoded paths moved to `constants.py`
+- Template-based script generation
+- Environment variable names centralized
+- Default values defined in one place
+
+### 3. **Path Handling with `pathlib.Path`**
+- Replaced `os.path.*` with `pathlib.Path`
+- More declarative and robust path operations
+- Built-in `.mkdir(parents=True, exist_ok=True)`
+- Cross-platform compatibility
+
+### 4. **Enhanced Error Handling**
+- Specific exception catching (`OSError`, `zipfile.BadZipFile`, `shutil.Error`)
+- Granular error reporting
+- Consistent error response structure
+- Better logging of specific failure points
+
+### 5. **Type Safety with TypedDict**
+- Defined response structures for all methods
+- Consistent API contracts
+- Better IDE support and documentation
+- Runtime compatibility with `Dict[str, Any]`
+
+### 6. **DRY Principle Implementation**
+- `_remove_if_exists()` helper for file removal
+- `_atomic_write()` for safe file writing
+- `_ensure_directories()` for directory creation
+- Unified file destination mapping
+
+### 7. **Atomic File Operations**
+- Safe script writing with temporary files
+- Prevents corruption during writes
+- Proper cleanup on failures
+- Consistent file permissions
+
+### 8. **Logger Injection**
+- Services accept optional logger parameter
+- Defaults to `decky.logger` when None
+- Enables unit testing with mock loggers
+- Better separation of concerns
+
+### 9. **Robust Configuration Parsing**
+- Regex-based parsing instead of string splitting
+- Handles edge cases (extra spaces, comments)
+- Template-based generation
+- Roundtrip consistency testing
+
+### 10. **Comprehensive Testing Framework**
+- Unit tests for each service
+- Mock filesystem with `pyfakefs`
+- Mock logger injection
+- Roundtrip testing for configuration
+- Environment variable mocking
+
+## 🧪 Testing
+
+### Running Tests
+```bash
+# Install test dependencies
+pip install -r requirements-test.txt
+
+# Run all tests
+pytest tests/
+
+# Run with coverage
+pytest tests/ --cov=lsfg_vk
+
+# Run specific test file
+pytest tests/test_installation.py
+```
+
+### Test Coverage
+- **Installation Service**: ZIP extraction, file copying, installation checking
+- **Configuration Service**: Script parsing, generation, roundtrip testing
+- **DLL Detection Service**: Environment variable priority, path checking
+- **Mock Integration**: All services work with mock loggers for testing
+
+## 🔄 Migration Guide
+
+### For Developers
+The public API remains unchanged - all existing frontend code will continue to work:
+
+```python
+# These calls remain identical
+plugin.install_lsfg_vk()
+plugin.check_lsfg_vk_installed()
+plugin.uninstall_lsfg_vk()
+plugin.get_lsfg_config()
+plugin.update_lsfg_config(...)
+plugin.check_lossless_scaling_dll()
+```
+
+### For Maintainers
+1. **Adding new features**: Add to appropriate service module
+2. **Constants**: Define in `constants.py`
+3. **New response types**: Add to `types.py`
+4. **Testing**: Add tests for new functionality
+5. **Common functionality**: Add to `base_service.py`
+
+## 📋 Benefits Achieved
+
+1. **Maintainability**: Easier to find and modify specific functionality
+2. **Testability**: Comprehensive unit test coverage
+3. **Reliability**: Atomic operations and better error handling
+4. **Documentation**: Clear type definitions and API contracts
+5. **Extensibility**: Easy to add new services or features
+6. **Code Quality**: Follows Python best practices and patterns
+
+## 🚀 Future Improvements
+
+### Next Steps (Not Yet Implemented)
+1. **Async/Sync Decision**: Evaluate if true async I/O is needed
+2. **Configuration Schema**: JSON schema validation for config files
+3. **Dependency Injection**: More sophisticated service container
+4. **Integration Tests**: End-to-end testing with real files
+5. **Performance Monitoring**: Metrics and logging for operations
+6. **Error Recovery**: More sophisticated error handling and retry logic
+
+### Potential Extensions
+- Plugin settings persistence
+- Multiple DLL version support
+- Automatic updates checking
+- Performance profiling integration
+- Steam integration improvements
+
+---
+
+This refactoring maintains 100% backward compatibility while significantly improving code quality, maintainability, and testability.