from django.core.management.base import BaseCommand
from uncloud_auth.models import User
from uncloud_pay.models import Order, Bill
from django.core.exceptions import ObjectDoesNotExist

from datetime import timedelta
from django.utils import timezone

BILL_PAYMENT_DELAY=timedelta(days=10)

class Command(BaseCommand):
    help = 'Generate bills and charge customers if necessary.'

    def add_arguments(self, parser):
        pass

    def handle(self, *args, **options):
        users = User.objects.all()
        print("Processing {} users.".format(users.count()))

        for user in users:
            # Fetch all the orders of a customer.
            orders = Order.objects.filter(owner=user)

            # Default values for next bill (if any). Only saved at the end of
            # this method, if relevant.
            next_bill = Bill(owner=user,
                       starting_date=timezone.now(), # Will be set to oldest unpaid order (means unpaid starting date).
                       ending_date=timezone.now(), # Bill covers everything until today.
                       due_date=timezone.now() + BILL_PAYMENT_DELAY)

            unpaid_orders = [] # Store orders in need of a payment.
            for order in orders:
                # Only bill if there is an 'unpaid period' on an active order.
                # XXX: Assume everything before latest bill is paid. => might be dangerous.
                try:
                    previous_bill = order.bill.latest('ending_date')
                except ObjectDoesNotExist:
                    previous_bill = None

                is_unpaid_period = True
                if order.ending_date and previous_bill != None:
                    is_unpaid_period = previous_bill.ending_date < order.ending_date

                if is_unpaid_period:
                    # Update bill starting date to match period.
                    if previous_bill == None:
                        next_bill.starting_date = order.starting_date
                    elif previous_bill.ending_date < next_bill.starting_date:
                        next_bill.starting_date = previous_bill.ending_date

                    # Add order to bill
                    unpaid_orders.append(order)

            # Save next_bill if it contains any unpaid product.
            if len(unpaid_orders) > 0:
              next_bill.save()

              # It is not possible to register many-to-many relationship before
              # the two end-objects are saved in database.
              for order in unpaid_orders:
                  order.bill.add(next_bill)

              print("Created bill {} for user {}".format(next_bill.uuid, user.username))

        # We're done for this round :-)
        print("=> Done.")