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 bluechips.model.tag import Tag
   6 from decimal import Decimal
   7 from datetime import datetime
   8 import random
   9
  10 class Expenditure(object):
  11     def __init__(self, spender=None, amount=Currency(0), description=u"",
  12                  date=None):
  13         self.spender = spender
  14         self.amount = amount
  15         self.description = description
  16         if self.date == None:
  17             self.date = datetime.now()
  18
  19     def __repr__(self):
  20         return '<Expenditure: spender: %s spent: %s>' % (self.spender,
  21                                                          self.amount)
  22
  23     def even_split(self):
  24         """
  25         Split up an expenditure evenly among the resident users
  26         """
  27
  28         residents = meta.Session.query(User).filter(User.resident==True)
  29         split_percentage = Decimal(100) / Decimal(residents.count())
  30         self.split(dict((resident, split_percentage) for resident in residents))
  31
  32     def split(self, split_dict, split_text_dict):
  33         """
  34         Split up an expenditure.
  35
  36         split_dict should be a dict mapping from bluechips.model:User
  37         objects to a decimal:Decimal object representing the percentage
  38         that user is responsible for.
  39
  40         Percentages will be normalized to sum to 100%.
  41
  42         If the split leaks or gains money due to rounding errors, the
  43         pennies will be randomly distributed to one of the users.
  44
  45         I mean, come on. You're already living together. Are you really
  46         going to squabble over a few pennies?
  47         """
  48
  49         map(meta.Session.delete, meta.Session.query(Split).\
  50                 filter_by(expenditure_id=self.id))
  51
  52         total = sum(split_dict.itervalues())
  53
  54         for user, share in split_dict.items():
  55             if share == 0:
  56                 del split_dict[user]
  57
  58         amounts_dict = dict()
  59
  60         for user, share in split_dict.iteritems():
  61             amounts_dict[user] = Currency((share * self.amount) / total)
  62
  63         difference = self.amount - sum(amounts_dict.itervalues())
  64
  65         if difference > 0:
  66             for i in xrange(difference):
  67                 winner = random.choice(amounts_dict.keys())
  68                 amounts_dict[winner] += Currency(1)
  69         elif difference < 0:
  70             for i in xrange(-difference):
  71                 winner = random.choice(amounts_dict.keys())
  72                 amounts_dict[winner] -= Currency(1)
  73
  74         for user, share in amounts_dict.iteritems():
  75             s = Split(self, user, share, split_text_dict[user])
  76             meta.Session.add(s)
  77
  78     def tag(self, tags):
  79         map(meta.Session.delete,
  80             meta.Session.query(Tag).filter_by(expenditure_id=self.id))
  81
  82         for tag in tags:
  83             t = Tag(self, tag)
  84             meta.Session.add(t)
  85
  86     def involves(self, user):
  87         "Returns True if ``user`` is involved in this expenditure."
  88         return (any((split.user == user) and (split.share != 0)
  89                     for split in self.splits) or
  90                 (self.spender == user))
  91
  92     def share(self, user):
  93         "Return the share corresponding to ``user``."
  94         shares = dict((split.user, split.share)
  95                       for split in self.splits)
  96         return shares.get(user, Currency(0))
  97
  98 __all__ = ['Expenditure']