Refactoring Surgeon

Expert code refactoring specialist focused on improving code quality without changing behavior.

Quick Start

1. Ensure tests exist - Never refactor without a safety net
2. Identify the smell - Name the specific code smell you're addressing
3. Make small changes - One refactoring at a time, commit frequently
4. Run tests after each change - Behavior must remain identical
5. Don't add features - Refactoring ≠ enhancement
6. Document significant changes - Explain the "why" for future maintainers

Core Capabilities

Category	Techniques
Extraction	Extract Method, Extract Class, Extract Interface
Movement	Move Method, Move Field, Inline Method
Simplification	Replace Conditional with Polymorphism, Decompose Conditional
Organization	Introduce Parameter Object, Replace Magic Numbers
Legacy Migration	Strangler Fig, Branch by Abstraction, Parallel Change

Code Smells Reference

Bloaters

┌─────────────────────┐    ┌─────────────────────┐    ┌─────────────────────┐
│    Long Method      │    │    Large Class      │    │   Long Parameter    │
│  > 20 lines?        │    │  > 200 lines?       │    │       List          │
│  → Extract Method   │    │  → Extract Class    │    │  → Parameter Object │
└─────────────────────┘    └─────────────────────┘    └─────────────────────┘

OO Abusers

┌─────────────────────┐    ┌─────────────────────┐    ┌─────────────────────┐
│  Switch Statements  │    │   Refused Bequest   │    │   Parallel          │
│  Type-checking?     │    │  Unused inheritance?│    │   Hierarchies       │
│  → Polymorphism     │    │  → Delegation       │    │  → Move Method      │
└─────────────────────┘    └─────────────────────┘    └─────────────────────┘

Change Preventers

┌─────────────────────┐    ┌─────────────────────┐
│  Divergent Change   │    │  Shotgun Surgery    │
│  One class, many    │    │  One change, many   │
│  reasons to change? │    │  classes affected?  │
│  → Extract Class    │    │  → Move/Inline      │
└─────────────────────┘    └─────────────────────┘

Reference Examples

Complete refactoring examples in ./references/:

File	Pattern	Use Case
extract-method.ts	Extract Method	Long methods → focused functions
replace-conditional-polymorphism.ts	Replace Conditional	switch/if → polymorphic classes
introduce-parameter-object.ts	Parameter Object	Long params → structured objects
strangler-fig-pattern.ts	Strangler Fig	Legacy code → gradual migration

Anti-Patterns (10 Critical Mistakes)

1. Big Bang Refactoring

Symptom: Rewriting entire modules in one massive change Fix: Strangler fig pattern, small incremental changes with tests

2. Refactoring Without Tests

Symptom: Changing structure without test coverage Fix: Write characterization tests first, add coverage for affected areas

3. Premature Abstraction

Symptom: Creating generic frameworks "for future flexibility" Fix: Wait for three concrete examples before abstracting (Rule of Three)

4. Renaming Without IDE Support

Symptom: Find-and-replace that misses occurrences Fix: Use IDE refactoring tools, search for usages first

5. Mixing Refactoring and Features

Symptom: Adding new functionality while restructuring Fix: Separate commits - refactor first, then add features

6. Ignoring Code Reviews

Symptom: Large refactoring PRs that are hard to review Fix: Small, focused PRs with clear commit messages

7. Over-Abstracting

Symptom: Three layers of abstraction for a simple operation Fix: YAGNI - start concrete, abstract when patterns emerge

8. Incomplete Refactoring

Symptom: Starting Extract Method but leaving partial duplication Fix: Complete the refactoring or revert - no half-measures

9. Refactoring Production During Incidents

Symptom: "I'll just clean this up while I'm here..." Fix: Never refactor during incidents - fix the bug, create a ticket

10. Not Measuring Improvement

Symptom: Refactoring without knowing if it helped Fix: Track metrics: complexity, test coverage, build time

Safety Checklist

Before Refactoring:

• Code compiles/runs successfully
• All tests pass
• Test coverage is adequate for area being refactored
• Commit current state (can rollback)

During Refactoring:

• Make small, incremental changes
• Run tests after each change
• Keep behavior identical
• Don't add features while refactoring

After Refactoring:

• All tests still pass
• No new warnings/errors
• Code is more readable
• Complexity metrics improved
• Document significant changes

Quality Checklist

• No behavior changes (tests prove this)
• Improved readability
• Reduced complexity (cyclomatic, cognitive)
• Better adherence to SOLID principles
• Removed duplication (DRY)
• More testable code
• Clear naming
• Appropriate abstractions (not over-engineered)

Validation Script

Run ./scripts/validate-refactoring.sh to check:

• Test coverage presence
• Code smell indicators
• Duplication patterns
• Complexity metrics
• SOLID violations
• Refactoring safety (git, uncommitted changes)

External Resources

• Refactoring.Guru
• Martin Fowler's Refactoring Catalog
• Working Effectively with Legacy Code