# BEFORE
def print_invoice(invoice):
    print("====================")
    print("INVOICE")
    print("====================")
    
    total = 0
    for item in invoice.items:
        print(f"{item.name}: ${item.price}")
        total += item.price
    
    print("--------------------")
    print(f"Total: ${total}")
    print("====================")

# AFTER
def print_invoice(invoice):
    print_header()
    total = print_line_items(invoice.items)
    print_footer(total)

def print_header():
    print("====================")
    print("INVOICE")
    print("====================")

def print_line_items(items):
    total = 0
    for item in items:
        print(f"{item.name}: ${item.price}")
        total += item.price
    return total

def print_footer(total):
    print("--------------------")
    print(f"Total: ${total}")
    print("====================")

# BEFORE
def calculate_shipping(order):
    if order.shipping_type == "standard":
        return order.weight * 1.5
    elif order.shipping_type == "express":
        return order.weight * 3.0 + 10
    elif order.shipping_type == "overnight":
        return order.weight * 5.0 + 25
    else:
        raise ValueError("Unknown shipping type")

# AFTER
class ShippingStrategy(ABC):
    @abstractmethod
    def calculate(self, weight: float) -> float:
        pass

class StandardShipping(ShippingStrategy):
    def calculate(self, weight: float) -> float:
        return weight * 1.5

class ExpressShipping(ShippingStrategy):
    def calculate(self, weight: float) -> float:
        return weight * 3.0 + 10

class OvernightShipping(ShippingStrategy):
    def calculate(self, weight: float) -> float:
        return weight * 5.0 + 25

def calculate_shipping(order):
    return order.shipping_strategy.calculate(order.weight)

# BEFORE
def create_event(name, start_date, end_date, start_time, end_time, timezone):
    ...

def validate_event(start_date, end_date, start_time, end_time, timezone):
    ...

# AFTER
@dataclass
class DateTimeRange:
    start_date: date
    end_date: date
    start_time: time
    end_time: time
    timezone: str
    
    def duration(self) -> timedelta:
        ...
    
    def is_valid(self) -> bool:
        ...

def create_event(name: str, when: DateTimeRange):
    ...

def validate_event(when: DateTimeRange):
    ...

# BEFORE
def calculate_discount(total):
    if total > 100:
        return total * 0.1
    elif total > 50:
        return total * 0.05
    return 0

if user.role == "admin":
    ...

# AFTER
BULK_DISCOUNT_THRESHOLD = 100
STANDARD_DISCOUNT_THRESHOLD = 50
BULK_DISCOUNT_RATE = 0.1
STANDARD_DISCOUNT_RATE = 0.05

class UserRole:
    ADMIN = "admin"
    USER = "user"
    GUEST = "guest"

def calculate_discount(total):
    if total > BULK_DISCOUNT_THRESHOLD:
        return total * BULK_DISCOUNT_RATE
    elif total > STANDARD_DISCOUNT_THRESHOLD:
        return total * STANDARD_DISCOUNT_RATE
    return 0

if user.role == UserRole.ADMIN:
    ...

1. VERIFY TESTS EXIST
   └─ No tests? Write characterization tests first
   
2. MAKE ONE SMALL CHANGE
   └─ Rename, extract, move - one at a time
   
3. RUN TESTS
   └─ All green? Continue
   └─ Red? Revert immediately
   
4. COMMIT
   └─ Small, atomic commits
   └─ "Refactor: Extract UserValidator class"
   
5. REPEAT
   └─ Next small change

Refactor: Extract method calculate_tax
Refactor: Rename User -> Customer  
Refactor: Move validation to separate module
Refactor: Replace conditionals with strategy pattern
Refactor: Remove dead code in payment module

## Refactoring Plan: [Module/Feature Name]

### Current Issues
| Code Smell | Location | Impact |
|------------|----------|--------|
| Long Method | order_service.py:45 | Hard to test |
| Duplicate Code | utils.py, helpers.py | Bug risk |

### Proposed Changes
1. **Extract `OrderValidator` class** from `OrderService`
   - Move validation methods
   - Inject as dependency
   
2. **Consolidate duplicate `format_currency`**
   - Keep in `utils.py`
   - Update imports

### Risk Assessment
- [ ] Tests exist for affected code
- [ ] Changes are reversible
- [ ] No public API changes (or documented)

### Execution Steps
- [ ] Step 1: Add missing tests
- [ ] Step 2: Extract class
- [ ] Step 3: Run tests
- [ ] Step 4: Update imports
- [ ] Step 5: Run tests
- [ ] Step 6: Remove old code

<!-- Add anti-patterns specific to your codebase -->

<!-- Example:
- God objects: UserManager, AppController
- Circular dependencies: services <-> utils
- Inconsistent naming: mix of camelCase and snake_case
-->

<!-- List known technical debt to address -->

<!-- Example:
| Area | Debt | Priority | Effort |
|------|------|----------|--------|
| Auth | Hardcoded roles | High | Medium |
| API | No input validation | Critical | High |
-->

<!-- Define what CAN and CANNOT be refactored freely -->

<!-- Example:
Safe to refactor (internal):
- /src/services/*
- /src/utils/*

Requires approval (public API):
- /src/api/*
- /src/sdk/*

Do not touch:
- /vendor/*
- /legacy/* (scheduled for removal)
-->

<!-- Add your project's conventions -->

<!-- Example:
- Max function length: 30 lines
- Max file length: 300 lines
- Max class methods: 10
- Naming: snake_case for Python, camelCase for JS
-->

# Add your refactoring-related commands:
#
# Run linter:
# 
# Run type checker:
#
# Find unused code:
#
# Check complexity:
#