#!/usr/bin/python3
# SPDX-License-Identifier: AGPL-3.0-or-later
"""
Module with utilities to generate a auth_pubtkt ticket and
sign it with the FreedomBox server's private key.
"""

import argparse
import base64
import datetime
import os

from OpenSSL import crypto

KEYS_DIRECTORY = '/etc/apache2/auth-pubtkt-keys'


def parse_arguments():
    """ Return parsed command line arguments as dictionary. """
    parser = argparse.ArgumentParser()
    subparsers = parser.add_subparsers(dest='subcommand', help='Sub command')

    subparsers.add_parser(
        'create-key-pair', help='create a key pair for the apache server '
        'to sign auth_pubtkt tickets')
    gen_tkt = subparsers.add_parser('generate-ticket',
                                    help='generate auth_pubtkt ticket')
    gen_tkt.add_argument('--uid', help='username of the user')
    gen_tkt.add_argument('--private-key-file',
                         help='path of the private key file of the server')
    gen_tkt.add_argument('--tokens',
                         help='tokens, usually containing the user groups')

    subparsers.required = True
    return parser.parse_args()


def subcommand_create_key_pair(_):
    """Create public/private key pair for signing the auth_pubtkt
    tickets.
    """
    private_key_file = os.path.join(KEYS_DIRECTORY, 'privkey.pem')
    public_key_file = os.path.join(KEYS_DIRECTORY, 'pubkey.pem')

    os.path.exists(KEYS_DIRECTORY) or os.mkdir(KEYS_DIRECTORY)

    if not all([
            os.path.exists(key_file)
            for key_file in [public_key_file, private_key_file]
    ]):
        pkey = crypto.PKey()
        pkey.generate_key(crypto.TYPE_RSA, 4096)

        with open(private_key_file, 'w') as priv_key_file:
            priv_key = crypto.dump_privatekey(crypto.FILETYPE_PEM,
                                              pkey).decode()
            priv_key_file.write(priv_key)

        with open(public_key_file, 'w') as pub_key_file:
            pub_key = crypto.dump_publickey(crypto.FILETYPE_PEM, pkey).decode()
            pub_key_file.write(pub_key)

        for fil in [public_key_file, private_key_file]:
            os.chmod(fil, 0o440)


def create_ticket(pkey, uid, validuntil, ip=None, tokens=None, udata=None,
                  graceperiod=None, extra_fields=None):
    """Create and return a signed mod_auth_pubtkt ticket."""
    fields = [
        f'uid={uid}',
        f'validuntil={int(validuntil)}',
        ip and f'cip={ip}',
        tokens and f'tokens={tokens}',
        graceperiod and f'graceperiod={int(graceperiod)}',
        udata and f'udata={udata}',
        extra_fields
        and ';'.join(['{}={}'.format(k, v) for k, v in extra_fields]),
    ]
    data = ';'.join(filter(None, fields))
    signature = 'sig={}'.format(sign(pkey, data))
    return ';'.join([data, signature])


def sign(pkey, data):
    """Calculates and returns ticket's signature."""
    sig = crypto.sign(pkey, data.encode(), 'sha512')
    return base64.b64encode(sig).decode()


def subcommand_generate_ticket(arguments):
    """Generate a mod_auth_pubtkt ticket using login credentials."""
    uid = arguments.uid
    private_key_file = arguments.private_key_file
    tokens = arguments.tokens
    with open(private_key_file, 'r') as fil:
        pkey = crypto.load_privatekey(crypto.FILETYPE_PEM, fil.read().encode())
    valid_until = minutes_from_now(12 * 60)
    grace_period = minutes_from_now(11 * 60)
    print(
        create_ticket(pkey, uid, valid_until, tokens=tokens,
                      graceperiod=grace_period))


def minutes_from_now(minutes):
    """Return a timestamp at the given number of minutes from now."""
    return seconds_from_now(minutes * 60)


def seconds_from_now(seconds):
    """Return a timestamp at the given number of seconds from now."""
    return (datetime.datetime.now() +
            datetime.timedelta(0, seconds)).timestamp()


def main():
    """Parse arguments and perform all duties."""
    arguments = parse_arguments()

    subcommand = arguments.subcommand.replace('-', '_')
    subcommand_method = globals()['subcommand_' + subcommand]
    subcommand_method(arguments)


if __name__ == '__main__':
    main()