#!/usr/bin/env python
"""

Generate a password hash, suitable for /etc/shadow

Inspired by this code from OpenStack:
https://github.com/openstack/nova/blob/stable/grizzly/nova/virt/disk/api.py#L549

Usage:
    mkpasswd <passwd> [--algo=<hash>]

Options:
    --algo=<hash>    One of: SHA-512, SHA-256, MD5, DES [default: SHA-256]

"""

from docopt import docopt

import crypt
import random


def generate_salt():
    salt_set = ('abcdefghijklmnopqrstuvwxyz'
                'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
                '0123456789./')
    salt = 16 * ' '
    return ''.join([random.choice(salt_set) for c in salt])


def main(passwd, algo):
    # encryption algo - id pairs for crypt()
    algos = {'SHA-512': '$6$', 'SHA-256': '$5$', 'MD5': '$1$', 'DES': ''}

    salt = generate_salt()
    result = crypt.crypt(passwd, algos[algo] + salt)
    return result


if __name__ == '__main__':
    args = docopt(__doc__)
    pw = main(passwd=args['<passwd>'], algo=args['--algo'])
    print pw