bluechips/model/expenditure.py

   1 from bluechips.model.user import User
   2 from bluechips.model.split import Split
   3 from bluechips.model import meta
   4 from bluechips.model.types import Currency
   5 from decimal import Decimal
   6 from datetime import datetime
   7 import random
   8
   9 class Expenditure(object):
  10     def __init__(self, spender=None, amount=Currency(0), description=u"",
  11                  date=None):
  12         self.spender = spender
  13         self.amount = amount
  14         self.description = description
  15         if self.date == None:
  16             self.date = datetime.now()
  17
  18     def __repr__(self):
  19         return '<Expenditure: spender: %s spent: %s>' % (self.spender,
  20                                                          self.amount)
  21
  22     def even_split(self):
  23         """
  24         Split up an expenditure evenly among the resident users
  25         """
  26
  27         residents = meta.Session.query(User).filter(User.resident==True)
  28         split_percentage = Decimal(100) / Decimal(residents.count())
  29         self.split(dict((resident, split_percentage) for resident in residents))
  30
  31     def split(self, split_dict):
  32         """
  33         Split up an expenditure.
  34
  35         split_dict should be a dict mapping from bluechips.model:User
  36         objects to a decimal:Decimal object representing the percentage
  37         that user is responsible for.
  38
  39         Percentages will be normalized to sum to 100%.
  40
  41         If the split leaks or gains money due to rounding errors, the
  42         pennies will be randomly distributed to one of the users.
  43
  44         I mean, come on. You're already living together. Are you really
  45         going to squabble over a few pennies?
  46         """
  47
  48         map(meta.Session.delete, meta.Session.query(Split).\
  49                 filter_by(expenditure_id=self.id))
  50
  51         total = sum(split_dict.itervalues())
  52
  53         for user, share in split_dict.items():
  54             if share == 0:
  55                 del split_dict[user]
  56
  57         amounts_dict = dict()
  58
  59         for user, share in split_dict.iteritems():
  60             amounts_dict[user] = Currency((share * self.amount) / total)
  61
  62         difference = self.amount - sum(amounts_dict.itervalues())
  63
  64         if difference > 0:
  65             for i in xrange(difference):
  66                 winner = random.choice(amounts_dict.keys())
  67                 amounts_dict[winner] += Currency(1)
  68         elif difference < 0:
  69             for i in xrange(-difference):
  70                 winner = random.choice(amounts_dict.keys())
  71                 amounts_dict[winner] -= Currency(1)
  72
  73         for user, share in amounts_dict.iteritems():
  74             s = Split(self, user, share)
  75             meta.Session.add(s)
  76
  77     def involves(self, user):
  78         "Returns True if ``user`` is involved in this expenditure."
  79         return (any((split.user == user) and (split.share != 0)
  80                     for split in self.splits) or
  81                 (self.spender == user))
  82
  83     def share(self, user):
  84         "Return the share corresponding to ``user``."
  85         shares = dict((split.user, split.share)
  86                       for split in self.splits)
  87         return shares.get(user, Currency(0))
  88
  89 __all__ = ['Expenditure']