Technical Deep Dive

### lambda_handler(event, context)
**Main entry point for Lambda execution**

**Parameters:**
- event (dict): API Gateway Lambda proxy integration event
  - requestContext.http.method (string): HTTP method (POST, OPTIONS)
  - headers.Authorization (string): JWT bearer token (format: "Bearer <token>")
  - body (string): JSON-encoded request body
- context (object): Lambda context object (unused)

**Request Body Structure:**
{
  "code": "string (required, will be uppercased)",
  "amount": "integer (required, > 0)",
  "description": "string (required, non-empty)",
  "total_allowed_uses": "integer (required, > 0)"
}

**Parameter Specifications:**
- code: Coupon code identifier
  - Automatically converted to uppercase
  - Must be unique across all coupons
  - Stripped of leading/trailing whitespace
- amount: Credit amount in smallest currency unit (e.g., cents)
  - Must be positive integer
  - Stored as Decimal in DynamoDB
- description: Human-readable coupon description
  - Required, non-empty after stripping whitespace
- total_allowed_uses: Maximum number of times coupon can be redeemed
  - Must be > 0
  - Stored as Decimal in DynamoDB

### _response(status_code, body)
**Formats API Gateway response with CORS headers**

**Parameters:**
- status_code (int): HTTP status code
- body (dict): Response payload (will be JSON-serialized)

**Returns:**
- dict: API Gateway Lambda proxy integration response format

### _decimal_default(obj)
**JSON serialization helper for Decimal types**

**Parameters:**
- obj (any): Object to serialize

**Returns:**
- float: If obj is Decimal
- Raises TypeError: If obj is not Decimal