From bfe0ee2c1af0f236102f1db687117a520ce531f5 Mon Sep 17 00:00:00 2001
From: Evan Broder <broder@mit.edu>
Date: Mon, 14 Jul 2008 06:14:06 +0000
Subject: [PATCH] Add functions to automatically split up an expenditure

---
 bluechips/lib/split.py | 69 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)
 create mode 100644 bluechips/lib/split.py

diff --git a/bluechips/lib/split.py b/bluechips/lib/split.py
new file mode 100644
index 0000000..b3295fd
--- /dev/null
+++ b/bluechips/lib/split.py
@@ -0,0 +1,69 @@
+"""
+Functions for handling splitting expenditures between people
+"""
+
+from bluechips import model
+from bluechips.model.meta import Session
+from bluechips.lib.helpers import round_currency
+from decimal import Decimal
+import random
+
+def even_split(e):
+    """
+    Split up an expenditure evenly among the resident users
+    
+    e should be a bluechips.model:Expenditure object
+    """
+    
+    residents = Session.query(model.User).filter(model.User.resident==True)
+    split_percentage = Decimal(100) / Decimal(residents.count())
+    split(e, dict((resident, split_percentage) for resident in residents))
+
+def split(e, split_dict):
+    """
+    Split up an expenditure.
+    
+    e should be a bluechips.model:Expenditure object.
+    
+    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?
+    """
+    
+    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] * e.amount)
+    
+    difference = e.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 = model.Split()
+        s.expenditure = e
+        s.user = user
+        s.share = share
+        Session.save(s)
+
+__all__ = ['split', 'even_split']
-- 
2.45.2