fixes #201 - ensure that if a periodic budget has $0 starting balance…

… and much greater spend than allocated, we properly calculate remaining for the payperiod

CHANGES.rst

@@ -4,6 +4,7 @@ Changelog
 Unreleased Changes
 ------------------
 
+* `Issue #201 <https://github.com/jantman/biweeklybudget/issues/201>`_ - Fix **major** bug in calculation of "Remaining" amount for pay periods, when one or more periodic budgets have a greater amount spent than allocated and a $0 starting balance. In that case, we were using the allocated amount instead of the spent amount (i.e. if we had a periodic budget with a $0 starting balance and a $2 ScheduledTransaction, and converted that ScheduledTransaction to a $1000 Transaction, the overall PayPeriod remaining amount would be based on the $2 not the $1000).
 * Add testing for Python 3.7, and make 3.7 the default for tests and tox environments.
 * TravisCI updates for Python 3.7.
 * Upgrade SQLAlchemy from 1.2.0 to 1.2.11 for `python 3 bug fix (4291) <https://docs.sqlalchemy.org/en/latest/changelog/changelog_12.html#change-2cca6c216347ab83d04c766452b48c1a>`_.

biweeklybudget/biweeklypayperiod.py

@@ -533,6 +533,7 @@ def _make_overall_sums(self):
         :return: dict describing sums for the pay period
         :rtype: dict
         """
+        budgets_total = Decimal('0.0')
         res = {
             'allocated': Decimal('0.0'),
             'spent': Decimal('0.0'),
@@ -548,10 +549,11 @@ def _make_overall_sums(self):
                 continue
             res['allocated'] += max(b['allocated'], b['budget_amount'])
             res['spent'] += b['spent']
-        if res['spent'] > res['allocated'] or self.is_in_past:
+            budgets_total += max(b['trans_total'], b['budget_amount'])
+        if self.is_in_past:
             res['remaining'] = res['income'] - res['spent']
         else:
-            res['remaining'] = res['income'] - res['allocated']
+            res['remaining'] = res['income'] - budgets_total
         return res
 
     def _trans_dict(self, t):