Validate a Shopping Cart

Problem Statement

In online food and grocery delivery platforms, shopping carts must be validated against real-time store catalogs before allowing a customer to proceed to checkout.

Implement the function validate_cart(store_info: dict, cart_items: list[dict]) -> dict that validates a user's cart against a store's catalog and ordering rules.

Rules

1. Empty Cart: If cart_items is empty, return an error "EMPTY_CART".
2. Invalid Quantity: Each item in cart_items must have an integer quantity > 0. If not, flag "INVALID_QUANTITY: ".
3. Catalog Existence: Each item_id must exist in store_info["catalog"]. If not found, flag "ITEM_NOT_FOUND: ".
4. Inventory Check: Multiple entries with the same item_id in cart_items should be consolidated (summing their quantities). For each existing item with valid quantities, if total_quantity > catalog[item_id]["inventory"], flag "INSUFFICIENT_INVENTORY: ".
5. Minimum Order Value: If there are no catalog or inventory errors, compute the cart's subtotal (sum(catalog[item_id]["price"] * total_quantity)). If subtotal < store_info["min_order_value"], flag "BELOW_MIN_ORDER".

Errors should be collected into a list. Order errors deterministically: list item-level errors in the order of their first appearance in cart_items, followed by "BELOW_MIN_ORDER" if applicable. An item should not be flagged for INSUFFICIENT_INVENTORY if it already failed the ITEM_NOT_FOUND or INVALID_QUANTITY check.

Function Signature

def validate_cart(store_info: dict, cart_items: list[dict]) -> dict:
    pass

Input and Output Format

• store_info: A dictionary with:
  • "min_order_value" (float): Minimum monetary value required to place an order.
  • "catalog" (dict): Maps string item_id to {"price": float, "inventory": int}.
• cart_items: A list of dictionaries, each containing "item_id" (str) and "quantity" (int).

Return a dictionary with:

• "is_valid" (bool): True if errors is empty, otherwise False.
• "subtotal" (float): The subtotal rounded to 2 decimal places (return 0.0 if any item-level errors occurred).
• "errors" (list[str]): List of error strings.

Example 1

store_info = {
    "min_order_value": 15.00,
    "catalog": {
        "item_1": {"price": 5.50, "inventory": 10},
        "item_2": {"price": 12.00, "inventory": 1}
    }
}
cart_items = [
    {"item_id": "item_1", "quantity": 2},
    {"item_id": "item_2", "quantity": 2}
]

# Output:
# {
#     "is_valid": False,
#     "subtotal": 0.0,
#     "errors": ["INSUFFICIENT_INVENTORY: item_2"]
# }

Explanation: item_2 requested quantity is 2, but available inventory is only 1.

Example 2

store_info = {
    "min_order_value": 20.00,
    "catalog": {
        "item_1": {"price": 4.00, "inventory": 10}
    }
}
cart_items = [
    {"item_id": "item_1", "quantity": 2},
    {"item_id": "item_1", "quantity": 1}
]

# Output:
# {
#     "is_valid": False,
#     "subtotal": 0.0,
#     "errors": ["BELOW_MIN_ORDER"]
# }

Explanation: item_1 is consolidated to quantity 3. Total price is 3 * 4.00 = 12.00, which is below min_order_value of 20.00.

Constraints

• 0 = 0