Structured patterns and techniques for improving code quality through safe, behavior-preserving refactoring.

• Covers common code smells including long methods, deeply nested conditionals, primitive obsession, and feature envy with before/after examples
• Provides core refactoring techniques: extract method, replace conditional with polymorphism, introduce parameter objects, and replace magic numbers with constants
• Emphasizes safe refactoring workflow: ensure test coverage first, make small focused changes, run tests after each step, and commit frequently
• Includes decision framework for when to refactor (before features, after tests pass, during code review) and when to avoid it (without tests, under tight deadlines, on code being replaced)