bluechips/model/expenditure.py

   1 from user import User
   2 from split import Split
   3 from bluechips.model import meta
   4 from bluechips.model.types import Currency
   5 from decimal import Decimal
   6 import random
   7
   8 class Expenditure(object):
   9     def __repr__(self):
  10         return '<Expenditure: spender: %s spent: %s>' % (self.spender,
  11                                                          self.amount)
  12
  13     def even_split(self):
  14         """
  15         Split up an expenditure evenly among the resident users
  16         """
  17
  18         residents = meta.Session.query(User).filter(User.resident==True)
  19         split_percentage = Decimal(100) / Decimal(residents.count())
  20         self.split(dict((resident, split_percentage) for resident in residents))
  21
  22     def split(self, split_dict):
  23         """
  24         Split up an expenditure.
  25
  26         split_dict should be a dict mapping from bluechips.model:User
  27         objects to a decimal:Decimal object representing the percentage
  28         that user is responsible for.
  29
  30         Percentages will be normalized to sum to 100%.
  31
  32         If the split leaks or gains money due to rounding errors, the
  33         pennies will be randomly distributed to one of the users.
  34
  35         I mean, come on. You're already living together. Are you really
  36         going to squabble over a few pennies?
  37         """
  38
  39         map(meta.Session.delete, meta.Session.query(Split).\
  40                 filter_by(expenditure_id=self.id))
  41
  42         total = sum(split_dict.itervalues())
  43
  44         for user, share in split_dict.iteritems():
  45             split_dict[user] = share / total
  46
  47         amounts_dict = dict()
  48
  49         for user, share in split_dict.iteritems():
  50             amounts_dict[user] = Currency(split_dict[user] * self.amount)
  51
  52         difference = self.amount - sum(amounts_dict.itervalues())
  53
  54         if difference > 0:
  55             for i in xrange(difference * 100):
  56                 winner = random.choice(amounts_dict.keys())
  57                 amounts_dict[winner] += Currency(1)
  58         elif difference < 0:
  59             for i in xrange(difference * -100):
  60                 winner = random.choice(amounts_dict.keys())
  61                 amounts_dict[winner] -= Currency(1)
  62
  63         for user, share in amounts_dict.iteritems():
  64             s = Split()
  65             s.expenditure = self
  66             s.user = user
  67             s.share = share
  68             meta.Session.save(s)
  69
  70 __all__ = ['Expenditure']