Fix #35, round down money to cent

billy/models/subscription.py

@@ -7,6 +7,7 @@
 from billy.models.transaction import TransactionModel
 from billy.models.schedule import next_transaction_datetime
 from billy.utils.generic import make_guid
+from billy.utils.generic import round_down_cent
 
 
 class SubscriptionCanceledError(RuntimeError):
@@ -126,6 +127,7 @@ def cancel(self, guid, prorated_refund=False):
             #       such as day or hour granularity?
             rate = elapsed_seconds / total_seconds
             amount = previous_transaction.amount * rate
+            amount = round_down_cent(amount)
 
             tx_model = TransactionModel(self.session)
             # make sure we will not refund zero dollar
@@ -189,6 +191,7 @@ def yield_transactions(self, now=None):
                 if subscription.discount is not None:
                     # TODO: what about float number round up?
                     amount *= (1 - subscription.discount)
+                    amount = round_down_cent(amount)
                 # create the new transaction for this subscription
                 guid = tx_model.create(
                     subscription_guid=subscription.guid, 

billy/tests/test_models/test_subscription.py

@@ -263,7 +263,27 @@ def test_subscription_cancel_with_prorated_refund_and_discount(self):
         # so the amount of transaction is 7.5, and we refund half,
         # then the refund amount should be 3.75
         self.assertEqual(transaction.amount, decimal.Decimal('3.75'))
-        # TODO: what about float number round up issue?
+
+    def test_subscription_cancel_with_prorated_refund_rounding(self):
+        from billy.models.transaction import TransactionModel
+        model = self.make_one(self.session)
+        tx_model = TransactionModel(self.session)
+
+        with freeze_time('2013-06-01'):
+            with db_transaction.manager:
+                guid = model.create(
+                    customer_guid=self.customer_tom_guid,
+                    plan_guid=self.monthly_plan_guid,
+                )
+                model.yield_transactions()
+
+        # 17 / 30 days, the rate should be 0.56666...
+        with freeze_time('2013-06-18'):
+            with db_transaction.manager:
+                refund_guid = model.cancel(guid, prorated_refund=True)
+
+        transaction = tx_model.get(refund_guid)
+        self.assertEqual(transaction.amount, decimal.Decimal('5.66'))
 
     def test_subscription_cancel_with_zero_refund(self):
         model = self.make_one(self.session)

billy/tests/test_utils/test_generic.py

@@ -1,5 +1,4 @@
 from __future__ import unicode_literals
-import math
 import unittest
 
 
@@ -28,3 +27,25 @@ def test_make_api_key(self):
         # just make sure it is random
         api_keys = [make_api_key() for _ in range(1000)]
         self.assertEqual(len(set(api_keys)), 1000)
+
+    def test_round_down_cent(self):
+        from decimal import Decimal
+        from billy.utils.generic import round_down_cent
+
+        def assert_round_down(amount, expected):
+            self.assertEqual(
+                round_down_cent(Decimal(amount)), 
+                Decimal(expected)
+            )
+
+        assert_round_down('0.0', '0.0')
+        assert_round_down('0.1', '0.1')
+        assert_round_down('0.11', '0.11')
+        assert_round_down('1.0', '1.0')
+        assert_round_down('1.12', '1.12')
+        assert_round_down('123.0', '123.0')
+        assert_round_down('0.123', '0.12')
+        assert_round_down('0.1234', '0.12')
+        assert_round_down('0.5566', '0.55')
+        assert_round_down('0.7788', '0.77')
+        assert_round_down('1.23456789', '1.23')

billy/utils/generic.py

@@ -2,6 +2,7 @@
 
 import os
 import uuid
+import decimal
 
 B58_CHARS = b'123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'
 B58_BASE = len(B58_CHARS)
@@ -52,3 +53,12 @@ def make_api_key(size=32):
     # however, this is good enough currently
     random = os.urandom(size)
     return b58encode(random)
+
+def round_down_cent(amount):
+    """Round down money value to cent (truncate to), for example, $5.66666
+    will be rounded to $5.66
+
+    :param amount: the money amount to be rounded
+    :return: the rounded money amount
+    """
+    return amount.quantize(decimal.Decimal('.01'), rounding=decimal.ROUND_DOWN)