Skill: Refactor Expert

Category: Dev Expert Used By: All development agents

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Overview

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

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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

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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.

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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)

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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

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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.

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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

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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

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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

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