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 update_split(self):
  32         """
  33         Re-split an expenditure using the same percentages as what is
  34         currently in the database
  35         """
  36
  37         old_splits = meta.Session.query(Split).filter(Split.expenditure==self)
  38         split_dict = dict((s.user, Decimal(int(s.share))) for s in old_splits)
  39         self.split(split_dict)
  40
  41     def split(self, split_dict):
  42         """
  43         Split up an expenditure.
  44
  45         split_dict should be a dict mapping from bluechips.model:User
  46         objects to a decimal:Decimal object representing the percentage
  47         that user is responsible for.
  48
  49         Percentages will be normalized to sum to 100%.
  50
  51         If the split leaks or gains money due to rounding errors, the
  52         pennies will be randomly distributed to one of the users.
  53
  54         I mean, come on. You're already living together. Are you really
  55         going to squabble over a few pennies?
  56         """
  57
  58         map(meta.Session.delete, meta.Session.query(Split).\
  59                 filter_by(expenditure_id=self.id))
  60
  61         total = sum(split_dict.itervalues())
  62
  63         for user, share in split_dict.items():
  64             if share == 0:
  65                 del split_dict[user]
  66             else:
  67                 split_dict[user] = share / total
  68
  69         amounts_dict = dict()
  70
  71         for user, share in split_dict.iteritems():
  72             amounts_dict[user] = Currency(split_dict[user] * self.amount)
  73
  74         difference = self.amount - sum(amounts_dict.itervalues())
  75
  76         if difference > 0:
  77             for i in xrange(difference):
  78                 winner = random.choice(amounts_dict.keys())
  79                 amounts_dict[winner] += Currency(1)
  80         elif difference < 0:
  81             for i in xrange(-difference):
  82                 winner = random.choice(amounts_dict.keys())
  83                 amounts_dict[winner] -= Currency(1)
  84
  85         for user, share in amounts_dict.iteritems():
  86             s = Split(self, user, share)
  87             meta.Session.add(s)
  88
  89 __all__ = ['Expenditure']