# Copyright (c) 2009, David Buxton <david@gasmark6.com>
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"""Tools to convert between Python datetime instances and Microsoft times.
"""
from calendar import timegm
from datetime import datetime, timezone, tzinfo, timedelta

# 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: datetime) -> timedelta:
        return ZERO

    def tzname(self, dt: datetime) -> str:
        return "UTC"

    def dst(self, dt: datetime) -> timedelta:
        return ZERO


utc = UTC()


def dt_to_filetime(dt: datetime) -> int:
    """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'

    >>> "%.0f" % dt_to_filetime(datetime(1970, 1, 1, 0, 0, tzinfo=utc))
    '116444736000000000'

    >>> "%.0f" % dt_to_filetime(datetime(1970, 1, 1, 0, 0))
    '116444736000000000'

    >>> dt_to_filetime(datetime(2009, 7, 25, 23, 0, 0, 100))
    128930364000001000
    """
    if (dt.tzinfo is None) or (dt.tzinfo.utcoffset(dt) is None):
        dt = dt.replace(tzinfo=utc)
    ft = EPOCH_AS_FILETIME + (timegm(dt.timetuple()) * HUNDREDS_OF_NANOSECONDS)
    return ft + (dt.microsecond * 10)


def filetime_to_dt(ft: int) -> datetime:
    """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)

    >>> filetime_to_dt(128930364000001000)
    datetime.datetime(2009, 7, 25, 23, 0, 0, 100)
    """
    # Get seconds and remainder in terms of Unix epoch
    (s, ns100) = divmod(ft - EPOCH_AS_FILETIME, HUNDREDS_OF_NANOSECONDS)
    # Convert to datetime object
    dt = datetime.fromtimestamp(s, timezone.utc)
    # Add remainder in as microseconds. Python 3.2 requires an integer
    dt = dt.replace(microsecond=(ns100 // 10))
    return dt
