Skill: Refactor Expert

Category: Dev Expert Version: 1.1.0 Used By: All development agents

Overview

Guide safe, incremental refactoring that improves code quality without changing behavior.

Documentation Commands

Generate analysis and implementation plans before refactoring:

Command	Purpose	Output
`refactor:analyze <file>`	Code analysis document	`.claude/logs/refactors/{target}-analysis.md`
`refactor:plan <file>`	Implementation plan	`.claude/logs/refactors/{target}-plan.md`
`refactor:docs <file>`	Both documents	Analysis + Plan + Summary

Templates: templates/refactor-analysis.md, templates/refactor-plan.md

1. Refactoring Decision

Signal	Action
Code smell detected	Identify specific smell
Tests passing	Safe to refactor
No tests	Write tests FIRST
Large change needed	Break into small steps

Golden Rule: Never refactor and add features simultaneously.

2. Common Refactoring Patterns

Extract Method

// Before
function processOrder(order: Order) {
  // validate
  if (!order.items.length) throw new Error('Empty')
  if (!order.customer) throw new Error('No customer')
  // calculate
  let total = 0
  for (const item of order.items) {
    total += item.price * item.qty
  }
  return total
}

// After
function processOrder(order: Order) {
  validateOrder(order)
  return calculateTotal(order.items)
}

Replace Conditional with Polymorphism

// Before
function getPrice(type: string, base: number) {
  if (type === 'premium') return base * 0.8
  if (type === 'vip') return base * 0.7
  return base
}

// After
interface PricingStrategy { calculate(base: number): number }
class PremiumPricing implements PricingStrategy { calculate(base: number) { return base * 0.8 } }

Simplify Conditional

// Before
if (date.before(SUMMER_START) || date.after(SUMMER_END)) { charge = qty * winterRate }
else { charge = qty * summerRate }

// After
const isSummer = !date.before(SUMMER_START) && !date.after(SUMMER_END)
charge = qty * (isSummer ? summerRate : winterRate)

3. Code Smells → Refactoring

Smell	Refactoring
Long Method	Extract Method
Large Class	Extract Class
Long Parameter List	Introduce Parameter Object
Duplicate Code	Extract Method/Class
Feature Envy	Move Method
Data Clumps	Extract Class
Primitive Obsession	Replace with Object
Switch Statements	Replace with Polymorphism
Speculative Generality	Remove unused abstraction
Dead Code	Delete it

4. Safe Refactoring Steps

1. Ensure tests pass ✅
2. Make ONE small change
3. Run tests ✅
4. Commit
5. Repeat

Never: Multiple changes between test runs.

5. Refactoring Checklist

Before:

Tests exist and pass
Understand current behavior
Identify specific smell

During:

One change at a time
Tests after each change
Commit frequently

After:

All tests pass
Code cleaner
Behavior unchanged

Best Practices

Do's

Test first, refactor second
Small, incremental changes
Commit after each successful refactor
Use IDE refactoring tools
Document why (not what)

Don'ts

Refactor without tests
Mix refactoring with features
Make large changes at once
Refactor code you don't understand
Over-refactor working code

Related Commands

refactor <file> - Full refactoring workflow
refactor:analyze <file> - Analysis document only
refactor:plan <file> - Implementation plan only
refactor:docs <file> - Both documents
refactor:quick <file> - Skip approvals
refactor:performance <file> - Performance-focused
refactor:structure <file> - Structure-focused

Version: 1.1.0 | Last Updated: 2025-12-04

refactor-expert