Add initial generate-bills and charge-negative-balance uncloud-pay

commands

uncloud/uncloud_pay/serializers.py

@@ -1,6 +1,7 @@
 from django.contrib.auth import get_user_model
 from rest_framework import serializers
 from .models import *
+from .helpers import get_balance_for
 
 from functools import reduce
 from uncloud_vm.serializers import VMProductSerializer
@@ -10,7 +11,7 @@ class BillSerializer(serializers.ModelSerializer):
     class Meta:
         model = Bill
         fields = ['owner', 'amount', 'due_date', 'creation_date',
-                'starting_date', 'ending_date', 'paid']
+                'starting_date', 'ending_date']
 
 class PaymentSerializer(serializers.ModelSerializer):
     class Meta:
@@ -41,8 +42,4 @@ class UserSerializer(serializers.ModelSerializer):
         return reduce(lambda acc, entry: acc + entry.amount, entries, 0)
 
     def get_balance(self, user):
-        bills = self.__sum_balance(Bill.objects.filter(owner=user))
-        payments = self.__sum_balance(Payment.objects.filter(owner=user))
-        balance = payments - bills
-
-        return balance
+        return get_balance_for(user)