#!/usr/bin/env python

# An example that show how to use the python-gnucash bindings to make a
# simple vendor report.
# Copyright (C) 2007 ParIT Worker Co-operative <http://www.parit.ca>
# 
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
# 
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# 
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
# MA  02110-1301  USA
# 
# Authors: Mark Jenkins <mark@parit.ca>


# You need to start this with a suitable envionment for loading the gnucash
# libraries. Run as
# $ gnucash-env python example_AP_report.py
#
# instead of
# $ python example_AP_report.py


from gnucash import Session, GncNumeric
import sys


AP_ACCOUNT_NAME = "A/P"
VENDOR_NAME = "Electric Company"
ZERO = GncNumeric('0')
NEG_ONE = GncNumeric('-1')


def gnc_sum( iterable, start=ZERO ):
    """Like the built-in sum, but it uses a GncNumeric 0 as the default
    start value
    """
    return sum( iterable, start )

def extract_AP_parts_of_transaction( transaction ):
    """Go through a transaction, if the transaction involves the Vendor
    VENDOR_NAME, return the sum of any splits that apply to the AP account.
    Otherwise return GncNumeric 0
    """
    if transaction.description == VENDOR_NAME:
        return gnc_sum( split.value
                        for split in transaction.get_splits()
                        if split.account.name == AP_ACCOUNT_NAME )
    else:
        return ZERO



session = Session("example_books.xac")

try:
    AP = session.book.account_group.account_from_path(
        ("Liabilities", AP_ACCOUNT_NAME) )

    # Calculate the balance by going through every transaction and summing 
    # the splits against the AP account that associated with VENDOR_NAME
    balance = gnc_sum( extract_AP_parts_of_transaction(transaction)
                       for transaction in AP.get_transactions() )

    # negate the balance because we want to view liability balances as
    # positive values
    balance *= NEG_ONE

    print "Your balance with %s is $%s" % ( VENDOR_NAME, balance )
    
except Exception, (error):
    print sys.exc_info()

# even if there is an error we want to still try to close the session to
# get rid of any lock files
session.end()