## $Id$
##
## Copyright (C) 2011 Uli Fouquet & Henrik Bettermann
## 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
##
"""Datetimewidgets that are compatible with pytz.
"""
import datetime
import pytz
from zope.formlib.textwidgets import DatetimeWidget

class PytzDatetimeWidget(DatetimeWidget):
    """pytz-conform, non-ambigous UTC datetimes.

    While the standard formlib datetime widget makes use of
    zope.datetime and creates also not too reliable (or ambigous)
    datetimes based on local servertime, this widget provides
    non-ambigous UTC datetimes with a pytz timezone (pytz.utc).

    Using this widget for datetime data we always get clean UTC
    datetimes compatible with other Python packages (as pytz is more
    wide-spread than zope.datetime).

    For datetimes in other timezones we compute the correct UTC value
    and store this. A way to help making sure, only UTC-based values
    go into the DB.

    From zope.datetime, however, we save the parser abilities to
    interpret even bizarre entered data as some datetime.
    """
    def _toFieldValue(self, string):
        """Turn string into a UTC-based datetime.

        The TZ data is guaranteed to be pytz.utc.

        """
        value = super(PytzDatetimeWidget, self)._toFieldValue(string)
        if not isinstance(value, datetime.datetime):
            return value
        if value.tzinfo is None:
            return pytz.utc.localize(value)
        return value.astimezone(pytz.utc)