# Copyright Mercurial Contributors

#

# This software may be used and distributed according to the terms of the

# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

import functools

import stat

rangemask = 0x7FFFFFFF

@functools.total_ordering

class timestamp(tuple):

    """

    A Unix timestamp with optional nanoseconds precision,

    modulo 2**31 seconds.

    A 2-tuple containing:

    `truncated_seconds`: seconds since the Unix epoch,

    truncated to its lower 31 bits

    `subsecond_nanoseconds`: number of nanoseconds since `truncated_seconds`.

    When this is zero, the sub-second precision is considered unknown.

    """

    def __new__(cls, value):

        truncated_seconds, subsec_nanos = value

        value = (truncated_seconds & rangemask, subsec_nanos)

        return super(timestamp, cls).__new__(cls, value)

    def __eq__(self, other):

        self_secs, self_subsec_nanos = self

        other_secs, other_subsec_nanos = other

        return self_secs == other_secs and (

            self_subsec_nanos == other_subsec_nanos

            or self_subsec_nanos == 0

            or other_subsec_nanos == 0

        )

    def __gt__(self, other):

        self_secs, self_subsec_nanos = self

        other_secs, other_subsec_nanos = other

        if self_secs > other_secs:

            return True

        if self_secs < other_secs:

            return False

        if self_subsec_nanos == 0 or other_subsec_nanos == 0:

            # they are considered equal, so not "greater than"

            return False

        return self_subsec_nanos > other_subsec_nanos

def zero():

    """

    Returns the `timestamp` at the Unix epoch.

    """

    return tuple.__new__(timestamp, (0, 0))

def mtime_of(stat_result):

    """

    Takes an `os.stat_result`-like object and returns a `timestamp` object

    for its modification time.

    """

    try:

        # TODO: add this attribute to `osutil.stat` objects,

        # see `mercurial/cext/osutil.c`.

        #

        # This attribute is also not available on Python 2.

        nanos = stat_result.st_mtime_ns

    except AttributeError:

        # https://docs.python.org/2/library/os.html#os.stat_float_times

        # "For compatibility with older Python versions,

        #  accessing stat_result as a tuple always returns integers."

        secs = stat_result[stat.ST_MTIME]

        subsec_nanos = 0

    else:

        billion = int(1e9)

        secs = nanos // billion

        subsec_nanos = nanos % billion

    return timestamp((secs, subsec_nanos))