code-quality-standards.mdc

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description: Enforces SRP, complexity limits, performance patterns, and readability. Use when writing or reviewing code, refactoring, or when the user asks about code quality or standards.
globs: "**/*.{ts,tsx,js,jsx,py,go,cs,rs,java}"
---

# Code Quality Standards

## Single Responsibility Principle (SRP)
- Functions and classes do only ONE thing
- Functions should be 20-30 lines max
- Avoid function names containing "And" (e.g., `validateAndSave`) - split them
- Classes should not mix unrelated responsibilities

## Cyclomatic Complexity & Nesting
- **Hard limit:** No nesting deeper than 3 levels
- Use guard clauses (early returns) to flatten `if/else` structures
- Functions with >5 branch paths need refactoring

## Performance Patterns
- Avoid nested loops O(n^2) when Hash Map O(n) works
- Use Sets for containment checks, not Lists/Arrays
- **Never** put DB queries, API calls, or File I/O inside loops
- Batch fetch before the loop, then iterate over results
- Move invariant calculations outside loops
- Use StringBuilder/join for string concatenation in loops
- Use specific field selection instead of `SELECT *`

## Readability
- Variable names must be descriptive (no `x`, `data`, `tmp`, `ret`)
- No magic numbers - extract to named constants
- Consistent naming conventions throughout the codebase
- Clear function signatures with meaningful parameter names