Wiring initial user balance

uncloud/uncloud_pay/serializers.py

@@ -2,6 +2,8 @@ from django.contrib.auth import get_user_model
 from rest_framework import serializers
 from .models import *
 
+from functools import reduce
+
 class BillSerializer(serializers.ModelSerializer):
     class Meta:
         model = Bill
@@ -26,7 +28,16 @@ class OrderSerializer(serializers.ModelSerializer):
 class UserSerializer(serializers.ModelSerializer):
     class Meta:
         model = get_user_model()
-        fields = ['username', 'email']
+        fields = ['username', 'email', 'balance']
 
-    def get_balance(self, obj):
-        return 666
+    # Display current 'balance'
+    balance = serializers.SerializerMethodField('get_balance')
+    def __sum_balance(self, entries):
+        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