#!/usr/bin/env python3
#
# Copyright (C) 2018-2024 VyOS maintainers and contributors
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License version 2 or later as
# published by the Free Software Foundation.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

import os

from sys import exit
from ipaddress import IPv6Network

from vyos.base import Warning
from vyos.config import Config
from vyos.template import render
from vyos.utils.process import call
from vyos import ConfigError
from vyos import airbag
airbag.enable()

config_file = r'/run/radvd/radvd.conf'

def get_config(config=None):
    if config:
        conf = config
    else:
        conf = Config()
    base = ['service', 'router-advert']
    rtradv = conf.get_config_dict(base, key_mangling=('-', '_'),
                                  get_first_key=True,
                                  with_recursive_defaults=True)

    return rtradv

def verify(rtradv):
    if not rtradv:
        return None

    if 'interface' not in rtradv:
        return None

    for interface, interface_config in rtradv['interface'].items():
        interval_max = int(interface_config['interval']['max'])

        if 'prefix' in interface_config:
            for prefix, prefix_config in interface_config['prefix'].items():
                valid_lifetime = prefix_config['valid_lifetime']
                if valid_lifetime == 'infinity':
                    valid_lifetime = 4294967295

                preferred_lifetime = prefix_config['preferred_lifetime']
                if preferred_lifetime == 'infinity':
                    preferred_lifetime = 4294967295

                if not (int(valid_lifetime) >= int(preferred_lifetime)):
                    raise ConfigError('Prefix valid-lifetime must be greater then or equal to preferred-lifetime')

        if 'nat64prefix' in interface_config:
            nat64_supported_lengths = [32, 40, 48, 56, 64, 96]
            for prefix, prefix_config in interface_config['nat64prefix'].items():
                if IPv6Network(prefix).prefixlen not in nat64_supported_lengths:
                    raise ConfigError(f'Invalid NAT64 prefix length for "{prefix}", can only be one of: /' + ', /'.join(nat64_supported_lengths))

                if int(prefix_config['valid_lifetime']) < interval_max:
                    raise ConfigError(f'NAT64 valid-lifetime must not be smaller then "interval max" which is "{interval_max}"!')

        if 'name_server' in interface_config:
            if len(interface_config['name_server']) > 3:
                raise ConfigError('No more then 3 IPv6 name-servers supported!')

        if 'name_server_lifetime' in interface_config:
            # man page states:
            # The maximum duration how long the RDNSS entries are used for name
            # resolution. A value of 0 means the nameserver must no longer be
            # used. The value, if not 0, must be at least MaxRtrAdvInterval. To
            # ensure stale RDNSS info gets removed in a timely fashion, this
            # should not be greater than 2*MaxRtrAdvInterval.
            lifetime = int(interface_config['name_server_lifetime'])
            if lifetime > 0:
                if lifetime < int(interval_max):
                    raise ConfigError(f'RDNSS lifetime must be at least "{interval_max}" seconds!')
                if lifetime > 2* interval_max:
                    Warning(f'RDNSS lifetime should not exceed "{2 * interval_max}" which is two times "interval max"!')

    return None

def generate(rtradv):
    if not rtradv:
        return None

    render(config_file, 'router-advert/radvd.conf.j2', rtradv, permission=0o644)
    return None

def apply(rtradv):
    systemd_service = 'radvd.service'
    if not rtradv:
        # bail out early - looks like removal from running config
        call(f'systemctl stop {systemd_service}')
        if os.path.exists(config_file):
            os.unlink(config_file)

        return None

    call(f'systemctl reload-or-restart {systemd_service}')

    return None

if __name__ == '__main__':
    try:
        c = get_config()
        verify(c)
        generate(c)
        apply(c)
    except ConfigError as e:
        print(e)
        exit(1)