Code Generation Prompt Templates

```typescript
type CustomerTier = 'bronze' | 'silver' | 'gold';

const DISCOUNT_RATES: Record<CustomerTier, number> = {
 bronze: 0.05,
 silver: 0.10,
 gold: 0.20,
};

/**
 * Applies tiered discount to order total based on customer membership.
 * @param total - Order total before discount (must be non-negative)
 * @param customerTier - Customer's membership tier
 * @returns Discounted total, minimum $0
 * @throws {RangeError} If total is negative
 */
export function calculateDiscount(
 total: number,
 customerTier: CustomerTier | string
): number {
 if (total < 0) {
 throw new RangeError(`Total cannot be negative: ${total}`);
 }

 const discountRate = DISCOUNT_RATES[customerTier as CustomerTier] ?? 0;
 const discountedTotal = total * (1 - discountRate);
 
 return Math.max(0, discountedTotal);
}
```

**Implementation notes:**
- Used `Record` type for discount rates, easy to add new tiers
- Unknown tier falls back to 0% discount (returns original total)
- `Math.max(0...)` ensures we never return negative
- JSDoc comments for IDE support

```python
import threading
import time
from collections import defaultdict
from dataclasses import dataclass, field


@dataclass
class RateLimiter:
 """Sliding window rate limiter with automatic cleanup.
 
 Thread-safe rate limiter that tracks requests per user within a
 configurable time window.
 
 Example:
 limiter = RateLimiter(max_requests=100, window_seconds=60)
 if limiter.is_allowed('user123'):
 process_request()
 else:
 raise RateLimitExceeded(limiter.get_remaining('user123'))
 """
 
 max_requests: int
 window_seconds: int
 _requests: dict = field(default_factory=lambda: defaultdict(list))
 _lock: threading.Lock = field(default_factory=threading.Lock)
 
 def is_allowed(self, user_id: str) -> bool:
 """Check if request is allowed and record it if so."""
 with self._lock:
 self._cleanup(user_id)
 
 if len(self._requests[user_id]) >= self.max_requests:
 return False
 
 self._requests[user_id].append(time.time())
 return True
 
 def get_remaining(self, user_id: str) -> int:
 """Get number of requests remaining in current window."""
 with self._lock:
 self._cleanup(user_id)
 return max(0, self.max_requests - len(self._requests[user_id]))
 
 def reset(self, user_id: str) -> None:
 """Clear all tracked requests for a user."""
 with self._lock:
 self._requests.pop(user_id, None)
 
 def _cleanup(self, user_id: str) -> None:
 """Remove requests outside the current window."""
 cutoff = time.time() - self.window_seconds
 self._requests[user_id] = [
 ts for ts in self._requests[user_id] if ts > cutoff
 ]
```

**Implementation notes:**
- Uses `threading.Lock` for thread safety
- Sliding window via timestamp list (accurate but uses more memory than fixed window)
- Cleanup on every access keeps memory bounded
- `defaultdict` avoids key existence checks

```typescript
import { Router, Request, Response, NextFunction } from 'express';
import { z } from 'zod';
import { authMiddleware } from '../middleware/auth';
import { OrderService } from '../services/OrderService';
import { InsufficientStockError } from '../errors';

const router = Router();

// Request validation schema
const CreateOrderSchema = z.object({
 items: z.array(z.object({
 productId: z.string().uuid(),
 quantity: z.number().int().positive(),
 })).min(1, 'Order must have at least one item'),
 shippingAddress: z.object({
 street: z.string().min(1),
 city: z.string().min(1),
 state: z.string().length(2),
 zipCode: z.string().regex(/^\d{5}(-\d{4})?$/),
 }),
});

type CreateOrderRequest = z.infer<typeof CreateOrderSchema>;

/**
 * POST /api/v1/orders
 * Create a new order for the authenticated user
 */
router.post(
 '/api/v1/orders',
 authMiddleware,
 async (req: Request, res: Response, next: NextFunction) => {
 try {
 // Validate request body
 const validationResult = CreateOrderSchema.safeParse(req.body);
 if (!validationResult.success) {
 return res.status(400).json({
 error: 'VALIDATION_ERROR',
 details: validationResult.error.errors,
 });
 }

 const { items, shippingAddress } = validationResult.data;
 const userId = req.user!.id; // Set by authMiddleware

 // Create order (validates stock, calculates total, sends email)
 const orderService = new OrderService();
 const order = await orderService.createOrder({
 userId,
 items,
 shippingAddress,
 });

 return res.status(201).json({
 id: order.id,
 status: order.status,
 items: order.items,
 total: order.total,
 shippingAddress: order.shippingAddress,
 createdAt: order.createdAt,
 });
 } catch (error) {
 if (error instanceof InsufficientStockError) {
 return res.status(409).json({
 error: 'INSUFFICIENT_STOCK',
 message: error.message,
 productId: error.productId,
 available: error.availableQuantity,
 });
 }
 next(error); // Pass to error handler
 }
 }
);

export default router;
```

**Implementation notes:**
- Zod validation with detailed error messages
- Typed request body from schema inference
- Business logic delegated to OrderService (keeps controller thin)
- Specific error handling for known error types
- Unknown errors passed to global error handler

```typescript
interface ApiResponse {
 user: {
 first_name: string | null;
 last_name: string | null;
 email_address: string;
 created_at: string;
 };
 orders?: Array<{ id: string }>;
}

interface UserDisplay {
 name: string;
 email: string;
 memberSince: Date;
 orderCount: number;
}

/**
 * Transforms API user response to frontend display format.
 * Handles missing/null values gracefully.
 */
export function transformUserResponse(response: ApiResponse): UserDisplay {
 const { user, orders } = response;
 
 // Combine names, handling nulls
 const firstName = user.first_name?.trim() || '';
 const lastName = user.last_name?.trim() || '';
 const name = [firstName, lastName].filter(Boolean).join(' ') || 'Unknown';
 
 return {
 name,
 email: user.email_address,
 memberSince: new Date(user.created_at),
 orderCount: orders?.length ?? 0,
 };
}

// Usage examples:
// transformUserResponse({ user: { first_name: 'Jane', last_name: 'Doe', email_address: 'jane@example.com', created_at: '2024-01-15T10:30:00Z' }, orders: [{id: '1'}, {id: '2'}] })
// → { name: 'Jane Doe', email: 'jane@example.com', memberSince: Date, orderCount: 2 }

// transformUserResponse({ user: { first_name: null, last_name: null, email_address: 'anon@example.com', created_at: '2024-01-15T10:30:00Z' } })
// → { name: 'Unknown', email: 'anon@example.com', memberSince: Date, orderCount: 0 }
```

**Why this approach:**
- Explicit types for both input and output shapes
- Defensive handling of null/undefined with sensible defaults
- `filter(Boolean)` cleanly removes empty strings from name array
- Optional chaining + nullish coalescing for concise null handling