# 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 stat

rangemask = 0x7FFFFFFF

class timestamp(tuple):

    """

    A Unix timestamp with 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`.

    """

    def __new__(cls, value):

        truncated_seconds, subsec_nanos = value

        value = (truncated_seconds & rangemask, subsec_nanos)

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

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.

    """

    # 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]

    # For now

    subsec_nanos = 0

    return timestamp((secs, subsec_nanos))