#!/usr/bin/env python

# -*- coding: utf-8  -*-

################################################################################

#

#  Rattail -- Retail Software Framework

#  Copyright © 2010-2012 Lance Edgar

#

#  This file is part of Rattail.

#

#  Rattail is free software: you can redistribute it and/or modify it under the

#  terms of the GNU Affero General Public License as published by the Free

#  Software Foundation, either version 3 of the License, or (at your option)

#  any later version.

#

#  Rattail 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 Affero General Public License for

#  more details.

#

#  You should have received a copy of the GNU Affero General Public License

#  along with Rattail.  If not, see <http://www.gnu.org/licenses/>.

#

################################################################################

"""

``rattail.pricing`` -- Pricing Utilities

"""

__all__ = ['gross_margin']

def gross_margin(price, cost):

    """

    Calculate and return a gross margin percentage based on ``price`` and

    ``cost``.

    If ``price`` is empty (or zero), returns ``None``.

    If ``cost`` is empty (or zero), returns ``100``.

    """

    if not price:

        return None

    if not cost:

        return 100

    return 100 * (price - cost) / price