Skill: dev-refactor

Inline

Code refactoring to improve quality. Trigger when the user wants to clean up, restructure, or improve existing code.

Configuration

Property	Value
Context	inline
Pre-approved tools	None declared: the project's permission settings apply
Trigger	keywords: dev, refactor

Detailed description

Code Refactoring

Principles

1. Tests pass BEFORE and AFTER
2. Small incremental changes
3. One type of change at a time
4. Commit after each refactoring

Common techniques

Extract Function

// Before
function processOrder(order) {
  // 20 lines of validation
  // 30 lines of calculation
  // 10 lines of sending
}

// After
function processOrder(order) {
  validateOrder(order);
  const total = calculateTotal(order);
  sendConfirmation(order, total);
}

Extract Variable

// Before
if (user.age >= 18 && user.country === 'FR' && !user.banned) { }

// After
const isAdult = user.age >= 18;
const isFrench = user.country === 'FR';
const isActive = !user.banned;
if (isAdult && isFrench && isActive) { }

Replace Conditional with Polymorphism

// Before
function getPrice(type) {
  switch(type) {
    case 'basic': return 10;
    case 'premium': return 20;
  }
}

// After
interface Plan { getPrice(): number }
class BasicPlan implements Plan { getPrice() { return 10; } }
class PremiumPlan implements Plan { getPrice() { return 20; } }

Code Smells to detect

Smell	Refactoring
Long method	Extract Method
Large class	Extract Class
Duplicate code	Extract + Reuse
Long parameter list	Parameter Object
Feature envy	Move Method
Primitive obsession	Value Object

Reducing Entropy (Complexity reduction)

Complexity metrics

Metric	Alert threshold	How to measure
Cyclomatic complexity	> 10 per function	Number of branches (if/else/switch)
Nesting depth	> 3 levels	Nesting of if/for/while
Function length	> 50 lines	Number of lines
Number of parameters	> 4	Function parameters
Afferent/efferent coupling	Unstable ratio	Incoming/outgoing dependencies
File size	> 300 lines	Lines of code

Reduction techniques

Early Return (eliminate nesting)

// BEFORE: deep nesting (high entropy)
function process(user) {
  if (user) {
    if (user.isActive) {
      if (user.hasPermission) {
        return doWork(user);
      }
    }
  }
  return null;
}

// AFTER: early returns (low entropy)
function process(user) {
  if (!user) return null;
  if (!user.isActive) return null;
  if (!user.hasPermission) return null;
  return doWork(user);
}

Break down complex conditions

// BEFORE
if (user.age >= 18 && user.country === 'FR' && !user.banned && user.email.includes('@')) { }

// AFTER
const isEligible = user.age >= 18
  && user.country === 'FR'
  && !user.banned
  && isValidEmail(user.email);
if (isEligible) { }

Eliminate dead code

# Find unused exports
# Find functions never called
# Remove unused imports
# Remove obsolete comments
# Remove orphan files

Consolidate duplications

Rule of 3: refactor on the 3rd duplication, not before.
- 1st occurrence: write the code
- 2nd occurrence: note the duplication (comment)
- 3rd occurrence: extract into a function/module

Workflow

1. MEASURE current complexity (metrics)
2. Identify the code smell
3. Write/verify tests
4. Apply the refactoring
5. MEASURE complexity after (must decrease)
6. Verify tests
7. Commit
8. Repeat

Automatic triggering

This skill is automatically activated when:

• The matching keywords are detected in the conversation
• The task context matches the skill's domain

Triggering examples

• "I want to dev..."
• "I want to refactor..."

Context inline

Inline means the skill runs in the conversation (the default, no context key):

• Sees the full history
• Its work is visible as it happens
• Right for almost every skill

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Practical examples

1. Example: Extract Service Refactoring

Example: Extract Service Refactoring

Scenario

A controller has grown to handle business logic, validation, and notifications. Extract a service layer.

Before: Fat Controller

// controllers/order.controller.ts (BEFORE - 80+ lines of mixed concerns)
export async function createOrder(req: Request, res: Response) {
  // Validation mixed in controller
  if (!req.body.items || req.body.items.length === 0) {
    return res.status(400).json({ error: 'Items required' });
  }

  // Business logic in controller
  let total = 0;
  for (const item of req.body.items) {
    const product = await db.product.findUnique({ where: { id: item.productId } });
    if (!product) return res.status(404).json({ error: `Product ${item.productId} not found` });
    if (product.stock < item.quantity) return res.status(400).json({ error: 'Insufficient stock' });
    total += product.price * item.quantity;
    await db.product.update({ where: { id: item.productId }, data: { stock: { decrement: item.quantity } } });
  }

  const order = await db.order.create({ data: { userId: req.user.id, total, items: req.body.items } });

  // Side effect in controller
  await sendEmail(req.user.email, `Order ${order.id} confirmed`);
  await notifySlack(`New order: ${order.id} - $${total}`);

  res.status(201).json({ data: order });
}

After: Extracted Service

// services/order.service.ts (AFTER - single responsibility)
export class OrderService {
  constructor(
    private db: Database,
    private notifier: NotificationService,
  ) {}

  async create(userId: string, items: OrderItem[]): Promise<Order> {
    if (items.length === 0) throw new ValidationError('Items required');

    const total = await this.calculateAndReserveStock(items);
    const order = await this.db.order.create({
      data: { userId, total, items },
    });

    await this.notifier.orderCreated(order);
    return order;
  }

  private async calculateAndReserveStock(items: OrderItem[]): Promise<number> {
    let total = 0;
    for (const item of items) {
      const product = await this.db.product.findUniqueOrThrow(item.productId);
      if (product.stock < item.quantity) {
        throw new InsufficientStockError(item.productId);
      }
      total += product.price * item.quantity;
      await this.db.product.decrementStock(item.productId, item.quantity);
    }
    return total;
  }
}

// controllers/order.controller.ts (AFTER - thin controller)
export async function createOrder(req: Request, res: Response, next: NextFunction) {
  try {
    const order = await orderService.create(req.user.id, req.body.items);
    res.status(201).json({ data: order });
  } catch (error) {
    next(error);  // Error middleware handles status codes
  }
}

Refactoring Steps

1. Identify responsibilities: Validation, business logic, persistence, notifications
2. Create service class: Move business logic into OrderService
3. Extract domain errors: ValidationError, InsufficientStockError replace inline responses
4. Inject dependencies: Database and NotificationService via constructor
5. Thin controller: Only HTTP concerns (parse request, call service, send response)
6. Run tests: Existing tests should pass; add unit tests for service

Key Decisions

• Constructor injection: Dependencies explicit, easy to mock in tests
• Domain errors over HTTP errors: Service throws ValidationError, middleware maps to 400
• Private helper methods: calculateAndReserveStock keeps create() readable
• Notification abstraction: NotificationService wraps email + Slack (single responsibility)

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See also

• Back to skills
• Architecture