# 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.

import functools

import os

import stat

from .. import error

rangemask = 0x7FFFFFFF

@functools.total_ordering

class timestamp(tuple):

    """

    A Unix timestamp with optional nanoseconds precision,

    modulo 2**31 seconds.

    A 3-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.

    `second_ambiguous`: whether this timestamp is still "reliable"

    (see `reliable_mtime_of`) if we drop its sub-second component.

    """

    def __new__(cls, value):

        truncated_seconds, subsec_nanos, second_ambiguous = value

        value = (truncated_seconds & rangemask, subsec_nanos, second_ambiguous)

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

    def __eq__(self, other):

        raise error.ProgrammingError(

            'timestamp should never be compared directly'

        )

    def __gt__(self, other):

        raise error.ProgrammingError(

            'timestamp should never be compared directly'

        )

def get_fs_now(vfs):

    """return a timestamp for "now" in the current vfs

    This will raise an exception if no temporary files could be created.

    """

    tmpfd, tmpname = vfs.mkstemp()

    try:

        return mtime_of(os.fstat(tmpfd))

    finally:

        os.close(tmpfd)

        vfs.unlink(tmpname)

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, False))

def reliable_mtime_of(stat_result, present_mtime):

    """Same as `mtime_of`, but return `None` or a `Timestamp` with

    `second_ambiguous` set if the date might be ambiguous.

    A modification time is reliable if it is older than "present_time" (or

    sufficiently in the future).

    Otherwise a concurrent modification might happens with the same mtime.

    """

    file_mtime = mtime_of(stat_result)

    file_second = file_mtime[0]

    file_ns = file_mtime[1]

    boundary_second = present_mtime[0]

    boundary_ns = present_mtime[1]

    # If the mtime of the ambiguous file is younger (or equal) to the starting

    # point of the `status` walk, we cannot garantee that another, racy, write

    # will not happen right after with the same mtime and we cannot cache the

    # information.

    #

    # However if the mtime is far away in the future, this is likely some

    # mismatch between the current clock and previous file system operation. So

    # mtime more than one days in the future are considered fine.

    if boundary_second == file_second:

        if file_ns and boundary_ns:

            if file_ns < boundary_ns:

                return timestamp((file_second, file_ns, True))

        return None

    elif boundary_second < file_second < (3600 * 24 + boundary_second):

        return None

    else:

        return file_mtime