#!/usr/bin/env python
# Copyright (c) 2009, David Buxton <david@gasmark6.com>
# All rights reserved.
# 
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are
# met:
# 
#     * Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
#     * Redistributions in binary form must reproduce the above copyright
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
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"""Tools to convert between Python datetime instances and Microsoft times.
"""
from datetime import datetime, timedelta, tzinfo
from calendar import timegm


# http://support.microsoft.com/kb/167296
# How To Convert a UNIX time_t to a Win32 FILETIME or SYSTEMTIME
EPOCH_AS_FILETIME = 116444736000000000  # January 1, 1970 as MS file time
HUNDREDS_OF_NANOSECONDS = 10000000


ZERO = timedelta(0)
HOUR = timedelta(hours=1)


class UTC(tzinfo):
    """UTC"""
    def utcoffset(self, dt):
        return ZERO

    def tzname(self, dt):
        return "UTC"

    def dst(self, dt):
        return ZERO


utc = UTC()


def dt_to_filetime(dt):
    """Converts a datetime to Microsoft filetime format. If the object is
    time zone-naive, it is forced to UTC before conversion.

    >>> "%.0f" % dt_to_filetime(datetime(2009, 7, 25, 23, 0))
    '128930364000000000'

    >>> dt_to_filetime(datetime(1970, 1, 1, 0, 0, tzinfo=utc))
    116444736000000000L

    >>> dt_to_filetime(datetime(1970, 1, 1, 0, 0))
    116444736000000000L
    """
    if (dt.tzinfo is None) or (dt.tzinfo.utcoffset(dt) is None):
        dt = dt.replace(tzinfo=utc)
    return EPOCH_AS_FILETIME + (timegm(dt.timetuple()) * HUNDREDS_OF_NANOSECONDS)


def filetime_to_dt(ft):
    """Converts a Microsoft filetime number to a Python datetime. The new
    datetime object is time zone-naive but is equivalent to tzinfo=utc.

    >>> filetime_to_dt(116444736000000000)
    datetime.datetime(1970, 1, 1, 0, 0)

    >>> filetime_to_dt(128930364000000000)
    datetime.datetime(2009, 7, 25, 23, 0)
    """
    return datetime.utcfromtimestamp((ft - EPOCH_AS_FILETIME) / HUNDREDS_OF_NANOSECONDS)


if __name__ == "__main__":
    import doctest
    
    doctest.testmod()
    

