quicknotes/specs/code_quality_refactoring.md

# Code Quality Refactoring Specification

## Overview

This specification defines a comprehensive plan for refactoring the QuickNotes application to comply with the newly established code quality rules. These rules represent our commitment to maintainable, performant, and error-resistant code. The refactoring effort prioritizes the following rule sets:

1. Error Handling Standards
2. Code Quality Metrics
3. Performance Optimization

## Refactoring Scope

The refactoring targets all components of the QuickNotes application:

- Frontend (Svelte/SvelteKit)
- Backend (Go with Gin)
- Database interaction layer
- CI/CD pipeline and developer workflows

## Frontend Refactoring Plan

### Phase 1: Error Handling Refactoring

1. **Create Error Class Hierarchy**:
   - Implement a base `ApplicationError` class
   - Define specific error subtypes like `ApiError`, `ValidationError`, `NetworkError`
   - Add proper type information for all error classes

2. **Implement Error Boundaries**:
   - Add a global error boundary for the application
   - Create component-specific error boundaries for critical features
   - Implement standardized fallback UI components

3. **Adopt Typed Error Handling**:
   - Refactor all `catch` blocks to use instance checking
   - Ensure proper error logging with contextual information
   - Implement user-friendly error messages with toast notifications

4. **API Error Handling**:
   - Standardize API error response format
   - Implement error response parsers for typed handling
   - Ensure errors bubble up appropriately or are handled locally

### Phase 2: Code Quality Improvements

1. **Reduce Code Complexity**:
   - Identify and refactor functions with high cyclomatic complexity
   - Split large files (>500 lines) into smaller modules
   - Reduce nesting depth to maximum of 4 levels

2. **Enhance Documentation**:
   - Add JSDoc comments to all public functions and components
   - Document complex algorithms with clear explanations
   - Include examples for non-obvious functionality

3. **Test Coverage Improvements**:
   - Increase test coverage to meet minimum requirements
   - Focus on critical paths (>90% coverage)
   - Implement proper mocking for external dependencies

### Phase 3: Performance Optimization

1. **Core Web Vitals Optimization**:
   - Measure current performance metrics (LCP, FID, CLS, FCP)
   - Implement lazy loading for non-critical components
   - Optimize asset loading and rendering

2. **Bundle Size Reduction**:
   - Implement code splitting for routes
   - Tree-shake unused dependencies
   - Optimize CSS and JavaScript bundles

3. **Component Rendering Optimization**:
   - Identify and fix unnecessary re-renders
   - Implement memoization for expensive computations
   - Virtualize long lists (feeds, readlist items)

4. **Asset Optimization**:
   - Convert images to WebP format
   - Implement responsive image loading
   - Optimize SVGs and compress static assets

## Backend Refactoring Plan

### Phase 1: Error Handling Refactoring

1. **Implement Error Types**:
   - Create custom error types for domain-specific errors
   - Add error wrapping for proper context
   - Implement error response standardization

2. **Refactor Error Propagation**:
   - Ensure all functions properly return errors
   - Replace panics with proper error returns
   - Add context to errors with `fmt.Errorf` and `%w`

3. **Enhance Error Logging**:
   - Implement structured logging for errors
   - Include contextual information with errors
   - Ensure proper error level classification

4. **User-Facing Error Handling**:
   - Create user-friendly error messages
   - Sanitize sensitive information from errors
   - Implement proper HTTP status codes for API errors

### Phase 2: Code Quality Improvements

1. **Reduce Function Complexity**:
   - Refactor functions exceeding complexity limits
   - Break long functions into smaller, focused ones
   - Improve function and variable naming

2. **Enhance Documentation**:
   - Document all exported functions, types, and variables
   - Follow GoDoc conventions
   - Add examples for complex functionality

3. **Test Coverage Improvements**:
   - Increase test coverage to meet minimum requirements
   - Implement table-driven tests
   - Add integration tests for critical flows

### Phase 3: Performance Optimization

1. **Database Query Optimization**:
   - Eliminate N+1 query problems
   - Implement proper indexing
   - Use query explain and analyze for tuning

2. **API Response Time Improvement**:
   - Implement caching for frequent requests
   - Add pagination for large result sets
   - Optimize data retrieval patterns

3. **Resource Utilization**:
   - Profile memory usage and fix leaks
   - Optimize goroutine usage
   - Implement connection pooling

4. **Caching Implementation**:
   - Add in-memory caching for static data
   - Implement HTTP caching headers
   - Consider Redis for distributed caching

## Implementation Strategy

### Prioritization

1. Error handling refactoring (highest priority)
2. Critical performance issues affecting user experience
3. Code quality improvements that impact maintainability
4. Test coverage improvements
5. Documentation enhancements

### Phases and Timeline

**Phase 1 (Weeks 1-2)**: Error handling standardization
- Complete error class hierarchy
- Standardize error handling patterns
- Implement error boundaries

**Phase 2 (Weeks 3-4)**: Code quality improvements
- Reduce complexity in high-priority modules
- Fix critical maintainability issues
- Address test coverage gaps

**Phase 3 (Weeks 5-6)**: Performance optimization
- Fix critical performance bottlenecks
- Implement caching strategy
- Optimize rendering and bundle size

**Phase 4 (Weeks 7-8)**: Documentation and finalization
- Enhance documentation
- Address remaining issues
- Final testing and validation

### Version Control Workflow

All refactoring work should follow the version control workflow rule:

1. Create feature branches for each refactoring task:
   - `refactor/error-handling-frontend`
   - `refactor/error-handling-backend`
   - `refactor/performance-feeds-list`

2. Ensure commit messages follow conventional format:
   - `refactor(frontend): implement typed error handling`
   - `perf(api): optimize note retrieval query`
   - `test(backend): improve coverage for error cases`

3. Keep PRs focused and manageable (<400 lines of code)

## Testing and Validation

### Validation Metrics

1. **Code Quality**:
   - Linting passes with zero errors
   - Complexity metrics meet thresholds
   - No regressions in existing functionality

2. **Performance**:
   - API response times meet targets
   - Frontend rendering metrics improved
   - Bundle sizes reduced

3. **Error Handling**:
   - All edge cases properly handled
   - Error messages are user-friendly
   - Proper logging of errors

### Testing Approach

1. **Unit Tests**:
   - Test individual components and functions
   - Focus on error scenarios and edge cases
   - Meet or exceed coverage requirements

2. **Integration Tests**:
   - Test interactions between components
   - Verify error propagation works correctly
   - Test performance under typical conditions

3. **End-to-End Tests**:
   - Verify complete user flows
   - Test error recovery scenarios
   - Validate performance in production-like environment

## Conclusion

This refactoring plan provides a comprehensive approach to elevating the codebase quality to meet the new standards. By prioritizing error handling, code quality, and performance, we ensure that QuickNotes becomes more maintainable, robust, and performant while providing a better experience for users.