"""Wrapper to the POSIX crypt library call and associated functionality."""

import _crypt
import string as _string
from random import SystemRandom as _SystemRandom
from collections import namedtuple as _namedtuple


_saltchars = _string.ascii_letters + _string.digits + './'
_sr = _SystemRandom()


class _Method(_namedtuple('_Method', 'name ident salt_chars total_size')):

"""Class representing a salt method per the Modular Crypt Format or the
legacy 2-character crypt method."""

def __repr__(self):
return '<crypt.METHOD_{}>'.format(self.name)


def mksalt(method=None):
"""Generate a salt for the specified method.

If not specified, the strongest available method will be used.

"""
if method is None:
method = methods[0]
s = '${}$'.format(method.ident) if method.ident else ''
s += ''.join(_sr.choice(_saltchars) for char in range(method.salt_chars))
return s


def crypt(word, salt=None):
"""Return a string representing the one-way hash of a password, with a salt
prepended.

If ``salt`` is not specified or is ``None``, the strongest
available method will be selected and a salt generated. Otherwise,
``salt`` may be one of the ``crypt.METHOD_*`` values, or a string as
returned by ``crypt.mksalt()``.

"""
if salt is None or isinstance(salt, _Method):
salt = mksalt(salt)
return _crypt.crypt(word, salt)


# available salting/crypto methods
METHOD_CRYPT = _Method('CRYPT', None, 2, 13)
METHOD_MD5 = _Method('MD5', '1', 8, 34)
METHOD_SHA256 = _Method('SHA256', '5', 16, 63)
METHOD_SHA512 = _Method('SHA512', '6', 16, 106)

methods = []
for _method in (METHOD_SHA512, METHOD_SHA256, METHOD_MD5):
_result = crypt('', _method)
if _result and len(_result) == _method.total_size:
methods.append(_method)
methods.append(METHOD_CRYPT)
del _result, _method