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:

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

1. Refactoring Decision

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

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