#!/usr/bin/env python3
#
# Copyright (C) 2018-2020 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 copy import deepcopy

from vyos.config import Config
from vyos import ConfigError
from vyos.util import call
from vyos.template import render

from vyos import airbag
airbag.enable()

config_file = r'/run/dhcp-relay/dhcpv6.conf'

default_config_data = {
    'listen_addr': [],
    'upstream_addr': [],
    'options': [],
}

def get_config():
    relay = deepcopy(default_config_data)
    conf = Config()
    if not conf.exists('service dhcpv6-relay'):
        return None
    else:
        conf.set_level('service dhcpv6-relay')

    # Network interfaces/address to listen on for DHCPv6 query(s)
    if conf.exists('listen-interface'):
        interfaces = conf.list_nodes('listen-interface')
        for intf in interfaces:
            if conf.exists('listen-interface {0} address'.format(intf)):
                addr = conf.return_value('listen-interface {0} address'.format(intf))
                listen = addr + '%' + intf
                relay['listen_addr'].append(listen)

    # Upstream interface/address for remote DHCPv6 server
    if conf.exists('upstream-interface'):
        interfaces = conf.list_nodes('upstream-interface')
        for intf in interfaces:
            addresses = conf.return_values('upstream-interface {0} address'.format(intf))
            for addr in addresses:
                server = addr + '%' + intf
                relay['upstream_addr'].append(server)

    # Maximum hop count. When forwarding packets, dhcrelay discards packets
    # which have reached a hop count of COUNT. Default is 10. Maximum is 255.
    if conf.exists('max-hop-count'):
        count = '-c ' + conf.return_value('max-hop-count')
        relay['options'].append(count)

    if conf.exists('use-interface-id-option'):
        relay['options'].append('-I')

    return relay

def verify(relay):
    # bail out early - looks like removal from running config
    if relay is None:
        return None

    if len(relay['listen_addr']) == 0 or len(relay['upstream_addr']) == 0:
        raise ConfigError('Must set at least one listen and upstream interface addresses.')

    return None

def generate(relay):
    # bail out early - looks like removal from running config
    if relay is None:
        return None

    render(config_file, 'dhcpv6-relay/config.tmpl', relay)
    return None

def apply(relay):
    if relay is not None:
        call('systemctl restart isc-dhcp-relay6.service')
    else:
        # DHCPv6 relay support is removed in the commit
        call('systemctl stop isc-dhcp-relay6.service')
        if os.path.exists(config_file):
            os.unlink(config_file)

    return None

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