Move functions for splitting expenditures into Expenditure model

[bluechips.git] / bluechips / model / expenditure.py

diff --git a/bluechips/model/expenditure.py b/bluechips/model/expenditure.py
index c093e75cdf3f8219120d4af080c3e7fc13369a84..88d65b3b6ae52649cd62bc1723a4c69a981d671f 100644 (file)
--- a/bluechips/model/expenditure.py
+++ b/bluechips/model/expenditure.py
@@ -1,6 +1,70 @@
+from user import User
+from split import Split
+from bluechips.model import meta
+from bluechips.lib.helpers import round_currency
+from decimal import Decimal
+import random
+
 class Expenditure(object):
     def __repr__(self):
         return '<Expenditure: spender: %s spent: %s>' % (self.spender,
                                                          self.amount)
 
+    def even_split(self):
+        """
+        Split up an expenditure evenly among the resident users
+        """
+        
+        residents = meta.Session.query(User).filter(User.resident==True)
+        split_percentage = Decimal(100) / Decimal(residents.count())
+        self.split(dict((resident, split_percentage) for resident in residents))
+    
+    def split(self, split_dict):
+        """
+        Split up an expenditure.
+        
+        split_dict should be a dict mapping from bluechips.model:User
+        objects to a decimal:Decimal object representing the percentage
+        that user is responsible for.
+        
+        Percentages will be normalized to sum to 100%.
+        
+        If the split leaks or gains money due to rounding errors, the
+        pennies will be randomly distributed to one of the users.
+        
+        I mean, come on. You're already living together. Are you really
+        going to squabble over a few pennies?
+        """
+        
+        map(meta.Session.delete, meta.Session.query(Split).\
+                filter_by(expenditure_id=self.id))
+        
+        total = sum(split_dict.itervalues())
+        
+        for user, share in split_dict.iteritems():
+            split_dict[user] = share / total
+            
+        amounts_dict = dict()
+        
+        for user, share in split_dict.iteritems():
+            amounts_dict[user] = round_currency(split_dict[user] * self.amount)
+        
+        difference = self.amount - sum(amounts_dict.itervalues())
+        
+        if difference > 0:
+            for i in xrange(difference * 100):
+                winner = random.choice(amounts_dict.keys())
+                amounts_dict[winner] += Decimal('0.01')
+        elif difference < 0:
+            for i in xrange(difference * -100):
+                winner = random.choice(amounts_dict.keys())
+                amounts_dict[winner] -= Decimal('0.01')
+        
+        for user, share in amounts_dict.iteritems():
+            s = Split()
+            s.expenditure = self
+            s.user = user
+            s.share = share
+            meta.Session.save(s)
+
 __all__ = ['Expenditure']