order_processing.py

from typing import Any, Dict, List, Tuple

# Константы
DEFAULT_CURRENCY = "USD"
TAX_RATE = 0.21

COUPON_SAVE10 = "SAVE10"
COUPON_SAVE20 = "SAVE20"
COUPON_VIP = "VIP"

SAVE10_RATE = 0.10
SAVE20_RATE = 0.20
SAVE20_FALLBACK_RATE = 0.05
SAVE20_THRESHOLD = 200

VIP_FIXED_DISCOUNT = 50
VIP_LOW_SUBTOTAL_THRESHOLD = 100
VIP_LOW_SUBTOTAL_DISCOUNT = 10


def parse_request(request: Dict[str, Any]) -> Tuple[Any, Any, Any, Any]:
    user_id = request.get("user_id")
    items = request.get("items")
    coupon = request.get("coupon")
    currency = request.get("currency")
    return user_id, items, coupon, currency


def validate_basic_fields(user_id: Any, items: Any, currency: Any) -> str:
    if user_id is None:
        raise ValueError("user_id is required")
    if items is None:
        raise ValueError("items is required")
    if currency is None:
        currency = DEFAULT_CURRENCY
    return currency


def validate_items(items: Any) -> List[Dict[str, Any]]:
    if not isinstance(items, list):
        raise ValueError("items must be a list")
    if len(items) == 0:
        raise ValueError("items must not be empty")

    for it in items:
        if "price" not in it or "qty" not in it:
            raise ValueError("item must have price and qty")
        if it["price"] <= 0:
            raise ValueError("price must be positive")
        if it["qty"] <= 0:
            raise ValueError("qty must be positive")

    return items


def calculate_subtotal(items: List[Dict[str, Any]]) -> int:
    subtotal = 0
    for it in items:
        subtotal = subtotal + it["price"] * it["qty"]
    return subtotal


def calculate_discount(subtotal: int, coupon: Any) -> int:
    if coupon is None or coupon == "":
        return 0

    if coupon == COUPON_SAVE10:
        return int(subtotal * SAVE10_RATE)

    if coupon == COUPON_SAVE20:
        if subtotal >= SAVE20_THRESHOLD:
            return int(subtotal * SAVE20_RATE)
        return int(subtotal * SAVE20_FALLBACK_RATE)

    if coupon == COUPON_VIP:
        discount = VIP_FIXED_DISCOUNT
        if subtotal < VIP_LOW_SUBTOTAL_THRESHOLD:
            discount = VIP_LOW_SUBTOTAL_DISCOUNT
        return discount

    raise ValueError("unknown coupon")


def calculate_tax(total_after_discount: int) -> int:
    return int(total_after_discount * TAX_RATE)


def build_order_id(user_id: Any, items: List[Dict[str, Any]]) -> str:
    return str(user_id) + "-" + str(len(items)) + "-" + "X"


def process_checkout(request: Dict[str, Any]) -> Dict[str, Any]:
    user_id, items, coupon, currency = parse_request(request)

    currency = validate_basic_fields(user_id, items, currency)
    items = validate_items(items)

    subtotal = calculate_subtotal(items)
    discount = calculate_discount(subtotal, coupon)

    total_after_discount = subtotal - discount
    if total_after_discount < 0:
        total_after_discount = 0

    tax = calculate_tax(total_after_discount)
    total = total_after_discount + tax

    order_id = build_order_id(user_id, items)

    return {
        "order_id": order_id,
        "user_id": user_id,
        "currency": currency,
        "subtotal": subtotal,
        "discount": discount,
        "tax": tax,
        "total": total,
        "items_count": len(items),
    }