r"""UUID objects (universally unique identifiers) according to RFC 4122/9562.

This module provides immutable UUID objects (class UUID) and functions for
generating UUIDs corresponding to a specific UUID version as specified in
RFC 4122/9562, e.g., uuid1() for UUID version 1, uuid3() for UUID version 3,
and so on.

Note that UUID version 2 is deliberately omitted as it is outside the scope
of the RFC.

If all you want is a unique ID, you should probably call uuid1() or uuid4().
Note that uuid1() may compromise privacy since it creates a UUID containing
the computer's network address.  uuid4() creates a random UUID.

Typical usage:

    >>> import uuid

    # make a UUID based on the host ID and current time
    >>> uuid.uuid1()    # doctest: +SKIP
    UUID('a8098c1a-f86e-11da-bd1a-00112444be1e')

    # make a UUID using an MD5 hash of a namespace UUID and a name
    >>> uuid.uuid3(uuid.NAMESPACE_DNS, 'python.org')
    UUID('6fa459ea-ee8a-3ca4-894e-db77e160355e')

    # make a random UUID
    >>> uuid.uuid4()    # doctest: +SKIP
    UUID('16fd2706-8baf-433b-82eb-8c7fada847da')

    # make a UUID using a SHA-1 hash of a namespace UUID and a name
    >>> uuid.uuid5(uuid.NAMESPACE_DNS, 'python.org')
    UUID('886313e1-3b8a-5372-9b90-0c9aee199e5d')

    # make a UUID from a string of hex digits (braces and hyphens ignored)
    >>> x = uuid.UUID('{00010203-0405-0607-0809-0a0b0c0d0e0f}')

    # convert a UUID to a string of hex digits in standard form
    >>> str(x)
    '00010203-0405-0607-0809-0a0b0c0d0e0f'

    # get the raw 16 bytes of the UUID
    >>> x.bytes
    b'\x00\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\x0c\r\x0e\x0f'

    # make a UUID from a 16-byte string
    >>> uuid.UUID(bytes=x.bytes)
    UUID('00010203-0405-0607-0809-0a0b0c0d0e0f')

    # get the Nil UUID
    >>> uuid.NIL
    UUID('00000000-0000-0000-0000-000000000000')

    # get the Max UUID
    >>> uuid.MAX
    UUID('ffffffff-ffff-ffff-ffff-ffffffffffff')
"""

import os
import sys
import time

from enum import Enum, _simple_enum


__author__ = 'Ka-Ping Yee <ping@zesty.ca>'

# The recognized platforms - known behaviors
if sys.platform in {'win32', 'darwin', 'emscripten', 'wasi'}:
    _AIX = _LINUX = False
elif sys.platform == 'linux':
    _LINUX = True
    _AIX = False
else:
    import platform
    _platform_system = platform.system()
    _AIX     = _platform_system == 'AIX'
    _LINUX   = _platform_system in ('Linux', 'Android')

_MAC_DELIM = b':'
_MAC_OMITS_LEADING_ZEROES = False
if _AIX:
    _MAC_DELIM = b'.'
    _MAC_OMITS_LEADING_ZEROES = True

RESERVED_NCS, RFC_4122, RESERVED_MICROSOFT, RESERVED_FUTURE = [
    'reserved for NCS compatibility', 'specified in RFC 4122',
    'reserved for Microsoft compatibility', 'reserved for future definition']

int_ = int      # The built-in int type
bytes_ = bytes  # The built-in bytes type


@_simple_enum(Enum)
class SafeUUID:
    safe = 0
    unsafe = -1
    unknown = None


_UINT_128_MAX = (1 << 128) - 1
# 128-bit mask to clear the variant and version bits of a UUID integral value
_RFC_4122_CLEARFLAGS_MASK = ~((0xf000 << 64) | (0xc000 << 48))
# RFC 4122 variant bits and version bits to activate on a UUID integral value.
_RFC_4122_VERSION_1_FLAGS = ((1 << 76) | (0x8000 << 48))
_RFC_4122_VERSION_3_FLAGS = ((3 << 76) | (0x8000 << 48))
_RFC_4122_VERSION_4_FLAGS = ((4 << 76) | (0x8000 << 48))
_RFC_4122_VERSION_5_FLAGS = ((5 << 76) | (0x8000 << 48))
_RFC_4122_VERSION_6_FLAGS = ((6 << 76) | (0x8000 << 48))
_RFC_4122_VERSION_7_FLAGS = ((7 << 76) | (0x8000 << 48))
_RFC_4122_VERSION_8_FLAGS = ((8 << 76) | (0x8000 << 48))


class UUID:
    """Instances of the UUID class represent UUIDs as specified in RFC 4122.
    UUID objects are immutable, hashable, and usable as dictionary keys.
    Converting a UUID to a string with str() yields something in the form
    '12345678-1234-1234-1234-123456789abc'.  The UUID constructor accepts
    five possible forms: a similar string of hexadecimal digits, or a tuple
    of six integer fields (with 32-bit, 16-bit, 16-bit, 8-bit, 8-bit, and
    48-bit values respectively) as an argument named 'fields', or a string
    of 16 bytes (with all the integer fields in big-endian order) as an
    argument named 'bytes', or a string of 16 bytes (with the first three
    fields in little-endian order) as an argument named 'bytes_le', or a
    single 128-bit integer as an argument named 'int'.

    UUIDs have these read-only attributes:

        bytes       the UUID as a 16-byte string (containing the six
                    integer fields in big-endian byte order)

        bytes_le    the UUID as a 16-byte string (with time_low, time_mid,
                    and time_hi_version in little-endian byte order)

        fields      a tuple of the six integer fields of the UUID,
                    which are also available as six individual attributes
                    and two derived attributes. Those attributes are not
                    always relevant to all UUID versions:

                        The 'time_*' attributes are only relevant to version 1.

                        The 'clock_seq*' and 'node' attributes are only relevant
                        to versions 1 and 6.

                        The 'time' attribute is only relevant to versions 1, 6
                        and 7.

            time_low                the first 32 bits of the UUID
            time_mid                the next 16 bits of the UUID
            time_hi_version         the next 16 bits of the UUID
            clock_seq_hi_variant    the next 8 bits of the UUID
            clock_seq_low           the next 8 bits of the UUID
            node                    the last 48 bits of the UUID

            time                    the 60-bit timestamp for UUIDv1/v6,
                                    or the 48-bit timestamp for UUIDv7
            clock_seq               the 14-bit sequence number

        hex         the UUID as a 32-character hexadecimal string

        int         the UUID as a 128-bit integer

        urn         the UUID as a URN as specified in RFC 4122/9562

        variant     the UUID variant (one of the constants RESERVED_NCS,
                    RFC_4122, RESERVED_MICROSOFT, or RESERVED_FUTURE)

        version     the UUID version number (1 through 8, meaningful only
                    when the variant is RFC_4122)

        is_safe     An enum indicating whether the UUID has been generated in
                    a way that is safe for multiprocessing applications, via
                    uuid_generate_time_safe(3).
    """

    __slots__ = ('int', 'is_safe', '__weakref__')

    def __init__(self, hex=None, bytes=None, bytes_le=None, fields=None,
                       int=None, version=None,
                       *, is_safe=SafeUUID.unknown):
        r"""Create a UUID from either a string of 32 hexadecimal digits,
        a string of 16 bytes as the 'bytes' argument, a string of 16 bytes
        in little-endian order as the 'bytes_le' argument, a tuple of six
        integers (32-bit time_low, 16-bit time_mid, 16-bit time_hi_version,
        8-bit clock_seq_hi_variant, 8-bit clock_seq_low, 48-bit node) as
        the 'fields' argument, or a single 128-bit integer as the 'int'
        argument.  When a string of hex digits is given, curly braces,
        hyphens, and a URN prefix are all optional.  For example, these
        expressions all yield the same UUID:

        UUID('{12345678-1234-5678-1234-567812345678}')
        UUID('12345678123456781234567812345678')
        UUID('urn:uuid:12345678-1234-5678-1234-567812345678')
        UUID(bytes='\x12\x34\x56\x78'*4)
        UUID(bytes_le='\x78\x56\x34\x12\x34\x12\x78\x56' +
                      '\x12\x34\x56\x78\x12\x34\x56\x78')
        UUID(fields=(0x12345678, 0x1234, 0x5678, 0x12, 0x34, 0x567812345678))
        UUID(int=0x12345678123456781234567812345678)

        Exactly one of 'hex', 'bytes', 'bytes_le', 'fields', or 'int' must
        be given.  The 'version' argument is optional; if given, the resulting
        UUID will have its variant and version set according to RFC 4122,
        overriding the given 'hex', 'bytes', 'bytes_le', 'fields', or 'int'.

        is_safe is an enum exposed as an attribute on the instance.  It
        indicates whether the UUID has been generated in a way that is safe
        for multiprocessing applications, via uuid_generate_time_safe(3).
        """

        if [hex, bytes, bytes_le, fields, int].count(None) != 4:
            raise TypeError('one of the hex, bytes, bytes_le, fields, '
                            'or int arguments must be given')
        if int is not None:
            pass
        elif hex is not None:
            hex = hex.replace('urn:', '').replace('uuid:', '')
            hex = hex.strip('{}').replace('-', '')
            if len(hex) != 32:
                raise ValueError('badly formed hexadecimal UUID string')
            int = int_(hex, 16)
        elif bytes_le is not None:
            if len(bytes_le) != 16:
                raise ValueError('bytes_le is not a 16-char string')
            assert isinstance(bytes_le, bytes_), repr(bytes_le)
            bytes = (bytes_le[4-1::-1] + bytes_le[6-1:4-1:-1] +
                     bytes_le[8-1:6-1:-1] + bytes_le[8:])
            int = int_.from_bytes(bytes)  # big endian
        elif bytes is not None:
            if len(bytes) != 16:
                raise ValueError('bytes is not a 16-char string')
            assert isinstance(bytes, bytes_), repr(bytes)
            int = int_.from_bytes(bytes)  # big endian
        elif fields is not None:
            if len(fields) != 6:
                raise ValueError('fields is not a 6-tuple')
            (time_low, time_mid, time_hi_version,
             clock_seq_hi_variant, clock_seq_low, node) = fields
            if not 0 <= time_low < (1 << 32):
                raise ValueError('field 1 out of range (need a 32-bit value)')
            if not 0 <= time_mid < (1 << 16):
                raise ValueError('field 2 out of range (need a 16-bit value)')
            if not 0 <= time_hi_version < (1 << 16):
                raise ValueError('field 3 out of range (need a 16-bit value)')
            if not 0 <= clock_seq_hi_variant < (1 << 8):
                raise ValueError('field 4 out of range (need an 8-bit value)')
            if not 0 <= clock_seq_low < (1 << 8):
                raise ValueError('field 5 out of range (need an 8-bit value)')
            if not 0 <= node < (1 << 48):
                raise ValueError('field 6 out of range (need a 48-bit value)')
            clock_seq = (clock_seq_hi_variant << 8) | clock_seq_low
            int = ((time_low << 96) | (time_mid << 80) |
                   (time_hi_version << 64) | (clock_seq << 48) | node)
        if not 0 <= int <= _UINT_128_MAX:
            raise ValueError('int is out of range (need a 128-bit value)')
        if version is not None:
            if not 1 <= version <= 8:
                raise ValueError('illegal version number')
            # clear the variant and the version number bits
            int &= _RFC_4122_CLEARFLAGS_MASK
            # Set the variant to RFC 4122/9562.
            int |= 0x8000_0000_0000_0000  # (0x8000 << 48)
            # Set the version number.
            int |= version << 76
        object.__setattr__(self, 'int', int)
        object.__setattr__(self, 'is_safe', is_safe)

    @classmethod
    def _from_int(cls, value):
        """Create a UUID from an integer *value*. Internal use only."""
        assert 0 <= value <= _UINT_128_MAX, repr(value)
        self = object.__new__(cls)
        object.__setattr__(self, 'int', value)
        object.__setattr__(self, 'is_safe', SafeUUID.unknown)
        return self

    def __getstate__(self):
        d = {'int': self.int}
        if self.is_safe != SafeUUID.unknown:
            # is_safe is a SafeUUID instance.  Return just its value, so that
            # it can be un-pickled in older Python versions without SafeUUID.
            d['is_safe'] = self.is_safe.value
        return d

    def __setstate__(self, state):
        object.__setattr__(self, 'int', state['int'])
        # is_safe was added in 3.7; it is also omitted when it is "unknown"
        object.__setattr__(self, 'is_safe',
                           SafeUUID(state['is_safe'])
                           if 'is_safe' in state else SafeUUID.unknown)

    def __eq__(self, other):
        if isinstance(other, UUID):
            return self.int == other.int
        return NotImplemented

    # Q. What's the value of being able to sort UUIDs?
    # A. Use them as keys in a B-Tree or similar mapping.

    def __lt__(self, other):
        if isinstance(other, UUID):
            return self.int < other.int
        return NotImplemented

    def __gt__(self, other):
        if isinstance(other, UUID):
            return self.int > other.int
        return NotImplemented

    def __le__(self, other):
        if isinstance(other, UUID):
            return self.int <= other.int
        return NotImplemented

    def __ge__(self, other):
        if isinstance(other, UUID):
            return self.int >= other.int
        return NotImplemented

    def __hash__(self):
        return hash(self.int)

    def __int__(self):
        return self.int

    def __repr__(self):
        return '%s(%r)' % (self.__class__.__name__, str(self))

    def __setattr__(self, name, value):
        raise TypeError('UUID objects are immutable')

    def __str__(self):
        x = self.hex
        return f'{x[:8]}-{x[8:12]}-{x[12:16]}-{x[16:20]}-{x[20:]}'

    @property
    def bytes(self):
        return self.int.to_bytes(16)  # big endian

    @property
    def bytes_le(self):
        bytes = self.bytes
        return (bytes[4-1::-1] + bytes[6-1:4-1:-1] + bytes[8-1:6-1:-1] +
                bytes[8:])

    @property
    def fields(self):
        return (self.time_low, self.time_mid, self.time_hi_version,
                self.clock_seq_hi_variant, self.clock_seq_low, self.node)

    @property
    def time_low(self):
        return self.int >> 96

    @property
    def time_mid(self):
        return (self.int >> 80) & 0xffff

    @property
    def time_hi_version(self):
        return (self.int >> 64) & 0xffff

    @property
    def clock_seq_hi_variant(self):
        return (self.int >> 56) & 0xff

    @property
    def clock_seq_low(self):
        return (self.int >> 48) & 0xff

    @property
    def time(self):
        if self.version == 6:
            # time_hi (32) | time_mid (16) | ver (4) | time_lo (12) | ... (64)
            time_hi = self.int >> 96
            time_lo = (self.int >> 64) & 0x0fff
            return time_hi << 28 | (self.time_mid << 12) | time_lo
        elif self.version == 7:
            # unix_ts_ms (48) | ... (80)
            return self.int >> 80
        else:
            # time_lo (32) | time_mid (16) | ver (4) | time_hi (12) | ... (64)
            #
            # For compatibility purposes, we do not warn or raise when the
            # version is not 1 (timestamp is irrelevant to other versions).
            time_hi = (self.int >> 64) & 0x0fff
            time_lo = self.int >> 96
            return time_hi << 48 | (self.time_mid << 32) | time_lo

    @property
    def clock_seq(self):
        return (((self.clock_seq_hi_variant & 0x3f) << 8) |
                self.clock_seq_low)

    @property
    def node(self):
        return self.int & 0xffffffffffff

    @property
    def hex(self):
        return self.bytes.hex()

    @property
    def urn(self):
        return 'urn:uuid:' + str(self)

    @property
    def variant(self):
        if not self.int & (0x8000 << 48):
            return RESERVED_NCS
        elif not self.int & (0x4000 << 48):
            return RFC_4122
        elif not self.int & (0x2000 << 48):
            return RESERVED_MICROSOFT
        else:
            return RESERVED_FUTURE

    @property
    def version(self):
        # The version bits are only meaningful for RFC 4122/9562 UUIDs.
        if self.variant == RFC_4122:
            return int((self.int >> 76) & 0xf)


def _get_command_stdout(command, *args):
    import io, os, shutil, subprocess

    try:
        path_dirs = os.environ.get('PATH', os.defpath).split(os.pathsep)
        path_dirs.extend(['/sbin', '/usr/sbin'])
        executable = shutil.which(command, path=os.pathsep.join(path_dirs))
        if executable is None:
            return None
        # LC_ALL=C to ensure English output, stderr=DEVNULL to prevent output
        # on stderr (Note: we don't have an example where the words we search
        # for are actually localized, but in theory some system could do so.)
        env = dict(os.environ)
        env['LC_ALL'] = 'C'
        # Empty strings will be quoted by popen so we should just omit it
        if args != ('',):
            command = (executable, *args)
        else:
            command = (executable,)
        proc = subprocess.Popen(command,
                                stdout=subprocess.PIPE,
                                stderr=subprocess.DEVNULL,
                                env=env)
        if not proc:
            return None
        stdout, stderr = proc.communicate()
        return io.BytesIO(stdout)
    except (OSError, subprocess.SubprocessError):
        return None


# For MAC (a.k.a. IEEE 802, or EUI-48) addresses, the second least significant
# bit of the first octet signifies whether the MAC address is universally (0)
# or locally (1) administered.  Network cards from hardware manufacturers will
# always be universally administered to guarantee global uniqueness of the MAC
# address, but any particular machine may have other interfaces which are
# locally administered.  An example of the latter is the bridge interface to
# the Touch Bar on MacBook Pros.
#
# This bit works out to be the 42nd bit counting from 1 being the least
# significant, or 1<<41.  We'll prefer universally administered MAC addresses
# over locally administered ones since the former are globally unique, but
# we'll return the first of the latter found if that's all the machine has.
#
# See https://en.wikipedia.org/wiki/MAC_address#Universal_vs._local_(U/L_bit)

def _is_universal(mac):
    return not (mac & (1 << 41))


def _find_mac_near_keyword(command, args, keywords, get_word_index):
    """Searches a command's output for a MAC address near a keyword.

    Each line of words in the output is case-insensitively searched for
    any of the given keywords.  Upon a match, get_word_index is invoked
    to pick a word from the line, given the index of the match.  For
    example, lambda i: 0 would get the first word on the line, while
    lambda i: i - 1 would get the word preceding the keyword.
    """
    stdout = _get_command_stdout(command, args)
    if stdout is None:
        return None

    first_local_mac = None
    for line in stdout:
        words = line.lower().rstrip().split()
        for i in range(len(words)):
            if words[i] in keywords:
                try:
                    word = words[get_word_index(i)]
                    mac = int(word.replace(_MAC_DELIM, b''), 16)
                except (ValueError, IndexError):
                    # Virtual interfaces, such as those provided by
                    # VPNs, do not have a colon-delimited MAC address
                    # as expected, but a 16-byte HWAddr separated by
                    # dashes. These should be ignored in favor of a
                    # real MAC address
                    pass
                else:
                    if _is_universal(mac):
                        return mac
                    first_local_mac = first_local_mac or mac
    return first_local_mac or None


def _parse_mac(word):
    # Accept 'HH:HH:HH:HH:HH:HH' MAC address (ex: '52:54:00:9d:0e:67'),
    # but reject IPv6 address (ex: 'fe80::5054:ff:fe9' or '123:2:3:4:5:6:7:8').
    #
    # Virtual interfaces, such as those provided by VPNs, do not have a
    # colon-delimited MAC address as expected, but a 16-byte HWAddr separated
    # by dashes. These should be ignored in favor of a real MAC address
    parts = word.split(_MAC_DELIM)
    if len(parts) != 6:
        return
    if _MAC_OMITS_LEADING_ZEROES:
        # (Only) on AIX the macaddr value given is not prefixed by 0, e.g.
        # en0   1500  link#2      fa.bc.de.f7.62.4 110854824     0 160133733     0     0
        # not
        # en0   1500  link#2      fa.bc.de.f7.62.04 110854824     0 160133733     0     0
        if not all(1 <= len(part) <= 2 for part in parts):
            return
        hexstr = b''.join(part.rjust(2, b'0') for part in parts)
    else:
        if not all(len(part) == 2 for part in parts):
            return
        hexstr = b''.join(parts)
    try:
        return int(hexstr, 16)
    except ValueError:
        return


def _find_mac_under_heading(command, args, heading):
    """Looks for a MAC address under a heading in a command's output.

    The first line of words in the output is searched for the given
    heading. Words at the same word index as the heading in subsequent
    lines are then examined to see if they look like MAC addresses.
    """
    stdout = _get_command_stdout(command, args)
    if stdout is None:
        return None

    keywords = stdout.readline().rstrip().split()
    try:
        column_index = keywords.index(heading)
    except ValueError:
        return None

    first_local_mac = None
    for line in stdout:
        words = line.rstrip().split()
        try:
            word = words[column_index]
        except IndexError:
            continue

        mac = _parse_mac(word)
        if mac is None:
            continue
        if _is_universal(mac):
            return mac
        if first_local_mac is None:
            first_local_mac = mac

    return first_local_mac


# The following functions call external programs to 'get' a macaddr value to
# be used as basis for an uuid
def _ifconfig_getnode():
    """Get the hardware address on Unix by running ifconfig."""
    # This works on Linux ('' or '-a'), Tru64 ('-av'), but not all Unixes.
    keywords = (b'hwaddr', b'ether', b'address:', b'lladdr')
    for args in ('', '-a', '-av'):
        mac = _find_mac_near_keyword('ifconfig', args, keywords, lambda i: i+1)
        if mac:
            return mac
    return None

def _ip_getnode():
    """Get the hardware address on Unix by running ip."""
    # This works on Linux with iproute2.
    mac = _find_mac_near_keyword('ip', 'link', [b'link/ether'], lambda i: i+1)
    if mac:
        return mac
    return None

def _arp_getnode():
    """Get the hardware address on Unix by running arp."""
    import os, socket
    if not hasattr(socket, "gethostbyname"):
        return None
    try:
        ip_addr = socket.gethostbyname(socket.gethostname())
    except OSError:
        return None

    # Try getting the MAC addr from arp based on our IP address (Solaris).
    mac = _find_mac_near_keyword('arp', '-an', [os.fsencode(ip_addr)], lambda i: -1)
    if mac:
        return mac

    # This works on OpenBSD
    mac = _find_mac_near_keyword('arp', '-an', [os.fsencode(ip_addr)], lambda i: i+1)
    if mac:
        return mac

    # This works on Linux, FreeBSD and NetBSD
    mac = _find_mac_near_keyword('arp', '-an', [os.fsencode('(%s)' % ip_addr)],
                    lambda i: i+2)
    # Return None instead of 0.
    if mac:
        return mac
    return None

def _lanscan_getnode():
    """Get the hardware address on Unix by running lanscan."""
    # This might work on HP-UX.
    return _find_mac_near_keyword('lanscan', '-ai', [b'lan0'], lambda i: 0)

def _netstat_getnode():
    """Get the hardware address on Unix by running netstat."""
    # This works on AIX and might work on Tru64 UNIX.
    return _find_mac_under_heading('netstat', '-ian', b'Address')


# Import optional C extension at toplevel, to help disabling it when testing
try:
    import _uuid
    _generate_time_safe = getattr(_uuid, "generate_time_safe", None)
    _has_stable_extractable_node = _uuid.has_stable_extractable_node
    _UuidCreate = getattr(_uuid, "UuidCreate", None)
except ImportError:
    _uuid = None
    _generate_time_safe = None
    _has_stable_extractable_node = False
    _UuidCreate = None


def _unix_getnode():
    """Get the hardware address on Unix using the _uuid extension module."""
    if _generate_time_safe and _has_stable_extractable_node:
        uuid_time, _ = _generate_time_safe()
        return UUID(bytes=uuid_time).node

def _windll_getnode():
    """Get the hardware address on Windows using the _uuid extension module."""
    if _UuidCreate and _has_stable_extractable_node:
        uuid_bytes = _UuidCreate()
        return UUID(bytes_le=uuid_bytes).node

def _random_getnode():
    """Get a random node ID."""
    # RFC 9562, §6.10-3 says that
    #
    #   Implementations MAY elect to obtain a 48-bit cryptographic-quality
    #   random number as per Section 6.9 to use as the Node ID. [...] [and]
    #   implementations MUST set the least significant bit of the first octet
    #   of the Node ID to 1. This bit is the unicast or multicast bit, which
    #   will never be set in IEEE 802 addresses obtained from network cards.
    #
    # The "multicast bit" of a MAC address is defined to be "the least
    # significant bit of the first octet".  This works out to be the 41st bit
    # counting from 1 being the least significant bit, or 1<<40.
    #
    # See https://en.wikipedia.org/w/index.php?title=MAC_address&oldid=1128764812#Universal_vs._local_(U/L_bit)
    return int.from_bytes(os.urandom(6)) | (1 << 40)


# _OS_GETTERS, when known, are targeted for a specific OS or platform.
# The order is by 'common practice' on the specified platform.
# Note: 'posix' and 'windows' _OS_GETTERS are prefixed by a dll/dlload() method
# which, when successful, means none of these "external" methods are called.
# _GETTERS is (also) used by test_uuid.py to SkipUnless(), e.g.,
#     @unittest.skipUnless(_uuid._ifconfig_getnode in _uuid._GETTERS, ...)
if _LINUX:
    _OS_GETTERS = [_ip_getnode, _ifconfig_getnode]
elif sys.platform == 'darwin':
    _OS_GETTERS = [_ifconfig_getnode, _arp_getnode, _netstat_getnode]
elif sys.platform == 'win32':
    # bpo-40201: _windll_getnode will always succeed, so these are not needed
    _OS_GETTERS = []
elif _AIX:
    _OS_GETTERS = [_netstat_getnode]
else:
    _OS_GETTERS = [_ifconfig_getnode, _ip_getnode, _arp_getnode,
                   _netstat_getnode, _lanscan_getnode]
if os.name == 'posix':
    _GETTERS = [_unix_getnode] + _OS_GETTERS
elif os.name == 'nt':
    _GETTERS = [_windll_getnode] + _OS_GETTERS
else:
    _GETTERS = _OS_GETTERS

_node = None

def getnode():
    """Get the hardware address as a 48-bit positive integer.

    The first time this runs, it may launch a separate program, which could
    be quite slow.  If all attempts to obtain the hardware address fail, we
    choose a random 48-bit number with its eighth bit set to 1 as recommended
    in RFC 4122.
    """
    global _node
    if _node is not None:
        return _node

    for getter in _GETTERS + [_random_getnode]:
        try:
            _node = getter()
        except:
            continue
        if (_node is not None) and (0 <= _node < (1 << 48)):
            return _node
    assert False, '_random_getnode() returned invalid value: {}'.format(_node)


_last_timestamp = None

def uuid1(node=None, clock_seq=None):
    """Generate a UUID from a host ID, sequence number, and the current time.
    If 'node' is not given, getnode() is used to obtain the hardware
    address.  If 'clock_seq' is given, it is used as the sequence number;
    otherwise a random 14-bit sequence number is chosen."""

    # When the system provides a version-1 UUID generator, use it (but don't
    # use UuidCreate here because its UUIDs don't conform to RFC 4122).
    if _generate_time_safe is not None and node is clock_seq is None:
        uuid_time, safely_generated = _generate_time_safe()
        try:
            is_safe = SafeUUID(safely_generated)
        except ValueError:
            is_safe = SafeUUID.unknown
        # The version field is assumed to be handled by _generate_time_safe().
        return UUID(bytes=uuid_time, is_safe=is_safe)

    global _last_timestamp
    nanoseconds = time.time_ns()
    # 0x01b21dd213814000 is the number of 100-ns intervals between the
    # UUID epoch 1582-10-15 00:00:00 and the Unix epoch 1970-01-01 00:00:00.
    timestamp = nanoseconds // 100 + 0x01b21dd213814000
    if _last_timestamp is not None and timestamp <= _last_timestamp:
        timestamp = _last_timestamp + 1
    _last_timestamp = timestamp
    if clock_seq is None:
        import random
        clock_seq = random.getrandbits(14) # instead of stable storage
    time_low = timestamp & 0xffffffff
    time_mid = (timestamp >> 32) & 0xffff
    time_hi_version = (timestamp >> 48) & 0x0fff
    clock_seq_low = clock_seq & 0xff
    clock_seq_hi_variant = (clock_seq >> 8) & 0x3f
    if node is None:
        node = getnode()
    return UUID(fields=(time_low, time_mid, time_hi_version,
                        clock_seq_hi_variant, clock_seq_low, node), version=1)

def uuid3(namespace, name):
    """Generate a UUID from the MD5 hash of a namespace UUID and a name."""
    if isinstance(name, str):
        name = bytes(name, "utf-8")
    import hashlib
    h = hashlib.md5(namespace.bytes + name, usedforsecurity=False)
    int_uuid_3 = int.from_bytes(h.digest())
    int_uuid_3 &= _RFC_4122_CLEARFLAGS_MASK
    int_uuid_3 |= _RFC_4122_VERSION_3_FLAGS
    return UUID._from_int(int_uuid_3)

def uuid4():
    """Generate a random UUID."""
    int_uuid_4 = int.from_bytes(os.urandom(16))
    int_uuid_4 &= _RFC_4122_CLEARFLAGS_MASK
    int_uuid_4 |= _RFC_4122_VERSION_4_FLAGS
    return UUID._from_int(int_uuid_4)

def uuid5(namespace, name):
    """Generate a UUID from the SHA-1 hash of a namespace UUID and a name."""
    if isinstance(name, str):
        name = bytes(name, "utf-8")
    import hashlib
    h = hashlib.sha1(namespace.bytes + name, usedforsecurity=False)
    int_uuid_5 = int.from_bytes(h.digest()[:16])
    int_uuid_5 &= _RFC_4122_CLEARFLAGS_MASK
    int_uuid_5 |= _RFC_4122_VERSION_5_FLAGS
    return UUID._from_int(int_uuid_5)


_last_timestamp_v6 = None

def uuid6(node=None, clock_seq=None):
    """Similar to :func:`uuid1` but where fields are ordered differently
    for improved DB locality.

    More precisely, given a 60-bit timestamp value as specified for UUIDv1,
    for UUIDv6 the first 48 most significant bits are stored first, followed
    by the 4-bit version (same position), followed by the remaining 12 bits
    of the original 60-bit timestamp.
    """
    global _last_timestamp_v6
    import time
    nanoseconds = time.time_ns()
    # 0x01b21dd213814000 is the number of 100-ns intervals between the
    # UUID epoch 1582-10-15 00:00:00 and the Unix epoch 1970-01-01 00:00:00.
    timestamp = nanoseconds // 100 + 0x01b21dd213814000
    if _last_timestamp_v6 is not None and timestamp <= _last_timestamp_v6:
        timestamp = _last_timestamp_v6 + 1
    _last_timestamp_v6 = timestamp
    if clock_seq is None:
        import random
        clock_seq = random.getrandbits(14)  # instead of stable storage
    time_hi_and_mid = (timestamp >> 12) & 0xffff_ffff_ffff
    time_lo = timestamp & 0x0fff  # keep 12 bits and clear version bits
    clock_s = clock_seq & 0x3fff  # keep 14 bits and clear variant bits
    if node is None:
        node = getnode()
    # --- 32 + 16 ---   -- 4 --   -- 12 --  -- 2 --   -- 14 ---    48
    # time_hi_and_mid | version | time_lo | variant | clock_seq | node
    int_uuid_6 = time_hi_and_mid << 80
    int_uuid_6 |= time_lo << 64
    int_uuid_6 |= clock_s << 48
    int_uuid_6 |= node & 0xffff_ffff_ffff
    # by construction, the variant and version bits are already cleared
    int_uuid_6 |= _RFC_4122_VERSION_6_FLAGS
    return UUID._from_int(int_uuid_6)


_last_timestamp_v7 = None
_last_counter_v7 = 0  # 42-bit counter

def _uuid7_get_counter_and_tail():
    rand = int.from_bytes(os.urandom(10))
    # 42-bit counter with MSB set to 0
    counter = (rand >> 32) & 0x1ff_ffff_ffff
    # 32-bit random data
    tail = rand & 0xffff_ffff
    return counter, tail


def uuid7():
    """Generate a UUID from a Unix timestamp in milliseconds and random bits.

    UUIDv7 objects feature monotonicity within a millisecond.
    """
    # --- 48 ---   -- 4 --   --- 12 ---   -- 2 --   --- 30 ---   - 32 -
    # unix_ts_ms | version | counter_hi | variant | counter_lo | random
    #
    # 'counter = counter_hi | counter_lo' is a 42-bit counter constructed
    # with Method 1 of RFC 9562, §6.2, and its MSB is set to 0.
    #
    # 'random' is a 32-bit random value regenerated for every new UUID.
    #
    # If multiple UUIDs are generated within the same millisecond, the LSB
    # of 'counter' is incremented by 1. When overflowing, the timestamp is
    # advanced and the counter is reset to a random 42-bit integer with MSB
    # set to 0.

    global _last_timestamp_v7
    global _last_counter_v7

    nanoseconds = time.time_ns()
    timestamp_ms = nanoseconds // 1_000_000

    if _last_timestamp_v7 is None or timestamp_ms > _last_timestamp_v7:
        counter, tail = _uuid7_get_counter_and_tail()
    else:
        if timestamp_ms < _last_timestamp_v7:
            timestamp_ms = _last_timestamp_v7 + 1
        # advance the 42-bit counter
        counter = _last_counter_v7 + 1
        if counter > 0x3ff_ffff_ffff:
            # advance the 48-bit timestamp
            timestamp_ms += 1
            counter, tail = _uuid7_get_counter_and_tail()
        else:
            # 32-bit random data
            tail = int.from_bytes(os.urandom(4))

    unix_ts_ms = timestamp_ms & 0xffff_ffff_ffff
    counter_msbs = counter >> 30
    # keep 12 counter's MSBs and clear variant bits
    counter_hi = counter_msbs & 0x0fff
    # keep 30 counter's LSBs and clear version bits
    counter_lo = counter & 0x3fff_ffff
    # ensure that the tail is always a 32-bit integer (by construction,
    # it is already the case, but future interfaces may allow the user
    # to specify the random tail)
    tail &= 0xffff_ffff

    int_uuid_7 = unix_ts_ms << 80
    int_uuid_7 |= counter_hi << 64
    int_uuid_7 |= counter_lo << 32
    int_uuid_7 |= tail
    # by construction, the variant and version bits are already cleared
    int_uuid_7 |= _RFC_4122_VERSION_7_FLAGS
    res = UUID._from_int(int_uuid_7)

    # defer global update until all computations are done
    _last_timestamp_v7 = timestamp_ms
    _last_counter_v7 = counter
    return res


def uuid8(a=None, b=None, c=None):
    """Generate a UUID from three custom blocks.

    * 'a' is the first 48-bit chunk of the UUID (octets 0-5);
    * 'b' is the mid 12-bit chunk (octets 6-7);
    * 'c' is the last 62-bit chunk (octets 8-15).

    When a value is not specified, a pseudo-random value is generated.
    """
    if a is None:
        import random
        a = random.getrandbits(48)
    if b is None:
        import random
        b = random.getrandbits(12)
    if c is None:
        import random
        c = random.getrandbits(62)
    int_uuid_8 = (a & 0xffff_ffff_ffff) << 80
    int_uuid_8 |= (b & 0xfff) << 64
    int_uuid_8 |= c & 0x3fff_ffff_ffff_ffff
    # by construction, the variant and version bits are already cleared
    int_uuid_8 |= _RFC_4122_VERSION_8_FLAGS
    return UUID._from_int(int_uuid_8)


def main():
    """Run the uuid command line interface."""
    uuid_funcs = {
        "uuid1": uuid1,
        "uuid3": uuid3,
        "uuid4": uuid4,
        "uuid5": uuid5,
        "uuid6": uuid6,
        "uuid7": uuid7,
        "uuid8": uuid8,
    }
    uuid_namespace_funcs = ("uuid3", "uuid5")
    namespaces = {
        "@dns": NAMESPACE_DNS,
        "@url": NAMESPACE_URL,
        "@oid": NAMESPACE_OID,
        "@x500": NAMESPACE_X500
    }

    import argparse
    parser = argparse.ArgumentParser(
        formatter_class=argparse.ArgumentDefaultsHelpFormatter,
        description="Generate a UUID using the selected UUID function.",
    )
    parser.add_argument("-u", "--uuid",
                        choices=uuid_funcs.keys(),
                        default="uuid4",
                        help="function to generate the UUID")
    parser.add_argument("-n", "--namespace",
                        metavar=f"{{any UUID,{','.join(namespaces)}}}",
                        help="`uuid3`/`uuid5` only: "
                        "a UUID, or a well-known predefined UUID addressed "
                        "by namespace name")
    parser.add_argument("-N", "--name",
                        help="`uuid3`/`uuid5` only: "
                        "name used as part of generating the UUID")
    parser.add_argument("-C", "--count", metavar="NUM", type=int, default=1,
                        help="generate `NUM` fresh UUIDs")

    args = parser.parse_args()
    uuid_func = uuid_funcs[args.uuid]
    namespace = args.namespace
    name = args.name

    if args.uuid in uuid_namespace_funcs:
        if not namespace or not name:
            parser.error(
                "Incorrect number of arguments. "
                f"{args.uuid} requires a namespace and a name. "
                "Run 'python -m uuid -h' for more information."
            )
        if namespace in namespaces:
            namespace = namespaces[namespace]
        else:
            try:
                namespace = UUID(namespace)
            except ValueError as exc:
                parser.error(f"{exc}: {args.namespace!r}")
        for _ in range(args.count):
            print(uuid_func(namespace, name))
    else:
        for _ in range(args.count):
            print(uuid_func())


# The following standard UUIDs are for use with uuid3() or uuid5().

NAMESPACE_DNS = UUID('6ba7b810-9dad-11d1-80b4-00c04fd430c8')
NAMESPACE_URL = UUID('6ba7b811-9dad-11d1-80b4-00c04fd430c8')
NAMESPACE_OID = UUID('6ba7b812-9dad-11d1-80b4-00c04fd430c8')
NAMESPACE_X500 = UUID('6ba7b814-9dad-11d1-80b4-00c04fd430c8')

# RFC 9562 Sections 5.9 and 5.10 define the special Nil and Max UUID formats.

NIL = UUID('00000000-0000-0000-0000-000000000000')
MAX = UUID('ffffffff-ffff-ffff-ffff-ffffffffffff')

if __name__ == "__main__":
    main()
