code-refactoring

Expected outcome:

## Refactoring Plan

### Original Function: processOrder (100 lines)

### Changes Made:
1. **Extracted validateOrder()** - Handles input validation
2. **Extracted calculateTotal()** - Computes order total with tax and shipping
3. **Extracted checkInventory()** - Validates stock availability
4. **Extracted createOrder()** - Creates the order in database

### New Structure:
```typescript
async function processOrder(order: Order) {
validateOrder(order);
const total = calculateTotal(order);
await checkInventory(order);
return await createOrder(order, total);
}
```

### Behavior Preserved:
- [x] Same validation rules
- [x] Same total calculation
- [x] Same inventory checking
- [x] Same order creation

Expected outcome:

## Duplication Found

### Before (Duplicated):
```typescript
async function getActiveUsers() {
return await db.user.findMany({
where: { status: 'active', deletedAt: null },
select: { id: true, name: true, email: true }
});
}

async function getActivePremiumUsers() {
return await db.user.findMany({
where: { status: 'active', deletedAt: null, plan: 'premium' },
select: { id: true, name: true, email: true }
});
}
```

### After (DRY):
```typescript
async function getActiveUsers(filter: UserFilter = {}) {
return await db.user.findMany({
where: { status: 'active', deletedAt: null, ...filter },
select: { id: true, name: true, email: true }
});
}

// Usage: getActiveUsers() or getActiveUsers({ plan: 'premium' })
```

Expected outcome:

## SOLID Analysis

### Original: User class with 3 responsibilities
- Data storage (save to DB)
- Email sending
- Report generation

### Refactored Structure:

| Class | Responsibility |
|-------|----------------|
| User | Data container |
| UserRepository | Database operations |
| EmailService | Communication |
| UserReportGenerator | Reporting |

### Benefits:
- Each class has one reason to change
- Easier to test in isolation
- Flexible to swap implementations
- Better collaboration in teams