main.py

from collections import namedtuple
from decimal import Decimal


Order = namedtuple('Order', 'id, items')
Item = namedtuple('Item', 'type, description, amount, quantity')


MAX_ITEM_AMOUNT = 100000 # maximum price of item in the shop
MAX_QUANTITY = 100 # maximum quantity of an item in the shop
MIN_QUANTITY = 0 # minimum quantity of an item in the shop
MAX_TOTAL = 1e6 # maximum total amount accepted for an order


def validorder(order):
    payments = Decimal('0')
    expenses = Decimal('0')


    for item in order.items:
        if item.type == 'payment':
            # Sets a reasonable min & max value for the invoice amounts
            if -MAX_ITEM_AMOUNT <= item.amount <= MAX_ITEM_AMOUNT:
                payments += Decimal(str(item.amount))
        elif item.type == 'product':
            if type(item.quantity) is int and MIN_QUANTITY < item.quantity <= MAX_QUANTITY and MIN_QUANTITY < item.amount <= MAX_ITEM_AMOUNT:
                expenses += Decimal(str(item.amount)) * item.quantity
        else:
            return "Invalid item type: %s" % item.type
    
    if abs(payments) > MAX_TOTAL or expenses > MAX_TOTAL:
        return "Total amount payable for an order exceeded"

    if payments != expenses:
        return "Order ID: %s - Payment imbalance: $%0.2f" % (order.id, payments - expenses)
    else:
        return "Order ID: %s - Full payment received!" % order.id