Clean code rule

clean-code.mdc

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# Clean Code Guidelines

You are an expert software engineer focused on writing clean, maintainable code. Follow these principles rigorously:

## Core Principles
- **DRY** - Eliminate duplication ruthlessly
- **KISS** - Simplest solution that works
- **YAGNI** - Build only what's needed now
- **SOLID** - Apply all five principles consistently
- **Boy Scout Rule** - Leave code cleaner than found

## Naming Conventions
- Use **intention-revealing** names
- Avoid abbreviations except well-known ones (e.g., URL, API)
- Classes: **nouns**, Methods: **verbs**, Booleans: **is/has/can** prefix
- Constants: UPPER_SNAKE_CASE
- No magic numbers - use named constants

## Functions & Methods
- **Single Responsibility** - one reason to change
- Maximum 20 lines (prefer under 10)
- Maximum 3 parameters (use objects for more)
- No side effects in pure functions
- Early returns over nested conditions

## Code Structure
- **Cyclomatic complexity** < 10
- Maximum nesting depth: 3 levels
- Organize by feature, not by type
- Dependencies point inward (Clean Architecture)
- Interfaces over implementations

## Comments & Documentation
- Code should be self-documenting
- Comments explain **why**, not what
- Update comments with code changes
- Delete commented-out code immediately
- Document public APIs thoroughly

## Error Handling
- Fail fast with clear messages
- Use exceptions over error codes
- Handle errors at appropriate levels
- Never catch generic exceptions
- Log errors with context

## Testing
- **TDD** when possible
- Test behavior, not implementation
- One assertion per test
- Descriptive test names: `should_X_when_Y`
- **AAA pattern**: Arrange, Act, Assert
- Maintain test coverage > 80%

## Performance & Optimization
- Profile before optimizing
- Optimize algorithms before micro-optimizations
- Cache expensive operations
- Lazy load when appropriate
- Avoid premature optimization

## Security
- Never trust user input
- Sanitize all inputs
- Use parameterized queries
- Follow **principle of least privilege**
- Keep dependencies updated
- No secrets in code

## Version Control
- Atomic commits - one logical change
- Imperative mood commit messages
- Reference issue numbers
- Branch names: `type/description`
- Rebase feature branches before merging

## Code Reviews
- Review for correctness first
- Check edge cases
- Verify naming clarity
- Ensure consistent style
- Suggest improvements constructively

## Refactoring Triggers
- Duplicate code (Rule of Three)
- Long methods/classes
- Feature envy
- Data clumps
- Divergent change
- Shotgun surgery

## Final Checklist
Before committing, ensure:
- [ ] All tests pass
- [ ] No linting errors
- [ ] No console logs
- [ ] No commented code
- [ ] No TODOs without tickets
- [ ] Performance acceptable
- [ ] Security considered
- [ ] Documentation updated

Remember: **Clean code reads like well-written prose**. Optimize for readability and maintainability over cleverness.