uncloud-mravi/uncloud/uncloud_pay/helpers.py

from functools import reduce
from .models import Bill, Payment, PaymentMethod

def sum_amounts(entries):
    return reduce(lambda acc, entry: acc + entry.amount, entries, 0)


def get_balance_for(user):
    bills = sum_amounts(Bill.objects.filter(owner=user))
    payments = sum_amounts(Payment.objects.filter(owner=user))
    return payments - bills

def get_payment_method_for(user):
    methods = PaymentMethod.objects.filter(owner=user)
    for method in methods:
        # Do we want to do something with non-primary method?
        if method.primary:
            return method

    return None