Refactor Skill

Systematic code refactoring with progressive disclosure.

Workflow

1. Initial Assessment

• Scope: Identify files/modules to analyze
• Language: Detect programming language and idioms
• Test Coverage: Check if tests exist
• Quick Scan: Find code smells (file size, function length, complexity)

2. Deep Analysis

• God Classes: Classes or Interfaces with >8 public methods
• Long Functions: Functions >50 LOC or cyclomatic complexity >10
• Deep Nesting: Conditionals nested
• Large Files: Files >500 lines
• Parameter Overload: Public functions with >4 parameters
• SOLID Principles: Violations of SOLID design principles
• Coupling: High inter-module dependencies
• Duplication: Repeated code blocks (>=2 lines similar)
• Magic Values: Hardcoded numbers/strings without constants
• Poor Naming: Unclear variable/function names
• Dead Code: Unused functions, variables, imports
• Global State: Mutable global variables
• Error Handling: Missing error handling or overly broad catches
• Performance Bottlenecks: Inefficient algorithms, unnecessary loops
• Security Concerns: SQL injection risks, XSS vulnerabilities, exposed secrets
• Memory Leaks: Unclosed resources, circular references

3. Execute Refactoring

1. Pre-Refactor:

   • Ensure tests exist (warn if missing)
   • Run tests to establish baseline

2. Refactor Incrementally:

   • Apply one pattern at a time
   • Keep changes atomic
   • Preserve exact behavior
   • Update related documentation/comments

3. Post-Refactor:

   • Run tests after each change
   • Verify behavior unchanged
   • Update tests if needed (structure only)

Refactoring Patterns Catalog

Extract Function/Method

When: Function >30 LOC, doing multiple things, or code duplication

// Before
function processUser(user: User) {
  if (!user.email || !user.email.includes('@')) {
    throw new Error('Invalid email');
  }
  const hash = crypto.createHash('sha256').update(user.password).digest('hex');
  user.password = hash;
  db.save(user);
  logger.info(`User ${user.email} processed`);
}

// After
function processUser(user: User) {
  validateEmail(user.email);
  user.password = hashPassword(user.password);
  saveUser(user);
  logUserProcessed(user.email);
}

function validateEmail(email: string) {
  if (!email || !email.includes('@')) {
    throw new Error('Invalid email');
  }
}

function hashPassword(password: string): string {
  return crypto.createHash('sha256').update(password).digest('hex');
}

function saveUser(user: User) {
  db.save(user);
}

function logUserProcessed(email: string) {
  logger.info(`User ${email} processed`);
}

Extract Class/Module

When: Class >10 methods, multiple responsibilities

# Before
class UserManager:
    def create_user(self, data): ...
    def update_user(self, id, data): ...
    def delete_user(self, id): ...
    def send_email(self, user, subject, body): ...
    def send_sms(self, user, message): ...
    def validate_password(self, password): ...
    def hash_password(self, password): ...

# After
class UserRepository:
    def create(self, data): ...
    def update(self, id, data): ...
    def delete(self, id): ...

class NotificationService:
    def send_email(self, user, subject, body): ...
    def send_sms(self, user, message): ...

class PasswordManager:
    def validate(self, password): ...
    def hash(self, password): ...

Introduce Parameter Object

When: Functions with >4 parameters, parameters often used together

// Before
public void createOrder(String userId, String productId, int quantity,
                       String address, String city, String zipCode,
                       String paymentMethod, String cardNumber) {
    // ...
}

// After
public void createOrder(OrderRequest request) {
    // ...
}

class OrderRequest {
    private String userId;
    private String productId;
    private int quantity;
    private Address shippingAddress;
    private PaymentInfo payment;
}

Simplify Complex Conditionals

When: Nested conditionals >3 levels, hard to understand logic

// Before
func canProcess(order Order) bool {
    if order.Status == "pending" {
        if order.Amount > 0 {
            if order.Customer != nil {
                if order.Customer.IsActive && order.Customer.CreditScore > 600 {
                    return true
                }
            }
        }
    }
    return false
}

// After
func canProcess(order Order) bool {
    return order.isPending() &&
           order.hasValidAmount() &&
           order.hasActiveCustomer() &&
           order.hasGoodCredit()
}

func (o Order) isPending() bool {
    return o.Status == "pending"
}

func (o Order) hasValidAmount() bool {
    return o.Amount > 0
}

func (o Order) hasActiveCustomer() bool {
    return o.Customer != nil && o.Customer.IsActive
}

func (o Order) hasGoodCredit() bool {
    return o.Customer != nil && o.Customer.CreditScore > 600
}

Replace Magic Numbers/Strings

When: Hardcoded values without context

// Before
public decimal CalculateTax(decimal amount) {
    if (amount > 10000) {
        return amount * 0.25;
    }
    return amount * 0.15;
}

// After
private const decimal HIGH_VALUE_THRESHOLD = 10000m;
private const decimal HIGH_VALUE_TAX_RATE = 0.25m;
private const decimal STANDARD_TAX_RATE = 0.15m;

public decimal CalculateTax(decimal amount) {
    if (amount > HIGH_VALUE_THRESHOLD) {
        return amount * HIGH_VALUE_TAX_RATE;
    }
    return amount * STANDARD_TAX_RATE;
}

Invert Conditional Logic

When: Deeply nested conditionals, improve readability

// Before
public decimal CalculateTax(decimal amount) {
    if (IsValidAmount(amount)) {
        // complex tax calculation logic
        return computedTax;
    }
    return 0;
}

// After
public decimal CalculateTax(decimal amount) {
    if (!IsValidAmount(amount)) {
        return 0;
    }
    // complex tax calculation logic
    return computedTax;
}

Safety Rules

• Never change observable behavior
• Ensure tests exist before major refactoring
• Make atomic commits per refactoring step
• Run tests after each change
• Document breaking changes (if unavoidable)
• Preserve error handling behavior
• Maintain performance characteristics
• Keep API compatibility unless explicitly breaking