bluechips/lib/totals.py

   1 """
   2 Calculate the total state of the books
   3 """
   4
   5 from bluechips import model
   6 from bluechips.model.meta import Session
   7
   8 import sqlalchemy
   9
  10 from decimal import Decimal
  11
  12 def debts():
  13     # In this scheme, negative numbers represent money the house owes
  14     # the user, and positive numbers represent money the user owes the
  15     # house
  16     users = Session.query(model.User)
  17
  18     debts = {}
  19
  20     # First, credit everyone for expenditures they've made
  21     for user in users:
  22         debts[user] = -sum(map((lambda x: x.amount), user.expenditures))
  23
  24     # Next, debit everyone for expenditures that they have an
  25     # investment in (i.e. splits)
  26
  27     total_splits = Session.query(model.Split).\
  28         add_column(sqlalchemy.func.sum(model.Split.share), 'total_split').\
  29         group_by(model.Split.user_id)
  30
  31     for split, total_cents in total_splits:
  32         debts[split.user] += (total_cents / 100)
  33
  34     # Finally, move transfers around appropriately
  35     #
  36     # To keep this from getting to be expensive, have SQL sum up
  37     # transfers for us
  38
  39     transfer_q = Session.query(model.Transfer).\
  40         add_column(sqlalchemy.func.sum(model.Transfer.amount), 'total_amount')
  41     total_debits = transfer_q.group_by(model.Transfer.debtor_id)
  42     total_credits = transfer_q.group_by(model.Transfer.creditor_id)
  43
  44     for transfer, total_amount in total_debits:
  45         debts[transfer.debtor] -= total_amount
  46     for transfer, total_amount in total_credits:
  47         debts[transfer.creditor] += total_amount
  48
  49     return debts