bluechips/model/expenditure.py

   1 from sqlalchemy.ext.associationproxy import association_proxy
   2
   3 from bluechips.model.user import User
   4 from bluechips.model.split import Split
   5 from bluechips.model import meta
   6 from bluechips.model.types import Currency
   7 from bluechips.model.tag import create_tag
   8 from decimal import Decimal
   9 from datetime import datetime
  10 import random
  11
  12 class Expenditure(object):
  13     def __init__(self, spender=None, amount=Currency(0), description=u"",
  14                  date=None):
  15         self.spender = spender
  16         self.amount = amount
  17         self.description = description
  18         if self.date == None:
  19             self.date = datetime.now()
  20
  21     tags = association_proxy('_tags', 'name', creator=create_tag)
  22
  23     def __repr__(self):
  24         return '<Expenditure: spender: %s spent: %s>' % (self.spender,
  25                                                          self.amount)
  26
  27     def even_split(self):
  28         """
  29         Split up an expenditure evenly among the resident users
  30         """
  31
  32         residents = meta.Session.query(User).filter(User.resident==True)
  33         split_percentage = Decimal(100) / Decimal(residents.count())
  34         self.split(dict((resident, split_percentage) for resident in residents))
  35
  36     def split(self, split_dict, split_text_dict):
  37         """
  38         Split up an expenditure.
  39
  40         split_dict should be a dict mapping from bluechips.model:User
  41         objects to a decimal:Decimal object representing the percentage
  42         that user is responsible for.
  43
  44         Percentages will be normalized to sum to 100%.
  45
  46         If the split leaks or gains money due to rounding errors, the
  47         pennies will be randomly distributed to one of the users.
  48
  49         I mean, come on. You're already living together. Are you really
  50         going to squabble over a few pennies?
  51         """
  52
  53         map(meta.Session.delete, meta.Session.query(Split).\
  54                 filter_by(expenditure_id=self.id))
  55
  56         total = sum(split_dict.itervalues())
  57
  58         for user, share in split_dict.items():
  59             if share == 0:
  60                 del split_dict[user]
  61
  62         amounts_dict = dict()
  63
  64         for user, share in split_dict.iteritems():
  65             amounts_dict[user] = Currency((share * self.amount) / total)
  66
  67         difference = self.amount - sum(amounts_dict.itervalues())
  68
  69         if difference > 0:
  70             for i in xrange(difference):
  71                 winner = random.choice(amounts_dict.keys())
  72                 amounts_dict[winner] += Currency(1)
  73         elif difference < 0:
  74             for i in xrange(-difference):
  75                 winner = random.choice(amounts_dict.keys())
  76                 amounts_dict[winner] -= Currency(1)
  77
  78         for user, share in amounts_dict.iteritems():
  79             s = Split(self, user, share, split_text_dict[user])
  80             meta.Session.add(s)
  81
  82     def involves(self, user):
  83         "Returns True if ``user`` is involved in this expenditure."
  84         return (any((split.user == user) and (split.share != 0)
  85                     for split in self.splits) or
  86                 (self.spender == user))
  87
  88     def share(self, user):
  89         "Return the share corresponding to ``user``."
  90         shares = dict((split.user, split.share)
  91                       for split in self.splits)
  92         return shares.get(user, Currency(0))
  93
  94 __all__ = ['Expenditure']