#!/usr/bin/env python3
#
# Copyright (C) 2019 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/>.
#

# This migration script will remove the deprecated 'listen-on' statement
# from the dns forwarding service and will add the corresponding 
# listen-address nodes instead. This is required as PowerDNS can only listen
# on interface addresses and not on interface names.

from ipaddress import ip_interface
from sys import argv, exit
from vyos.ifconfig import Interface
from vyos.configtree import ConfigTree

if (len(argv) < 1):
    print("Must specify file name!")
    exit(1)

file_name = argv[1]

with open(file_name, 'r') as f:
    config_file = f.read()

config = ConfigTree(config_file)

base = ['service', 'dns', 'forwarding']
if not config.exists(base):
    # Nothing to do
    exit(0)

if config.exists(base + ['listen-on']):
    listen_intf = config.return_values(base + ['listen-on'])
    # Delete node with abandoned command
    config.delete(base + ['listen-on'])

    # retrieve interface addresses for every configured listen-on interface
    listen_addr = []
    for intf in listen_intf:
        # we need to evaluate the interface section before manipulating the 'intf' variable
        section = Interface.section(intf)
        if not section:
            raise ValueError(f'Invalid interface name {intf}')

        # we need to treat vif and vif-s interfaces differently,
        # both "real interfaces" use dots for vlan identifiers - those
        # need to be exchanged with vif and vif-s identifiers
        if intf.count('.') == 1:
            # this is a regular VLAN interface
            intf = intf.split('.')[0] + ' vif ' + intf.split('.')[1]
        elif intf.count('.') == 2:
            # this is a QinQ VLAN interface
            intf = intf.split('.')[0] + ' vif-s ' + intf.split('.')[1] + ' vif-c ' +  intf.split('.')[2]

        # retrieve corresponding interface addresses in CIDR format
        # those need to be converted in pure IP addresses without network information
        path = ['interfaces', section, intf, 'address']
        try:
            for addr in config.return_values(path):
                listen_addr.append( ip_interface(addr).ip )
        except:
            # Some interface types do not use "address" option (e.g. OpenVPN)
            # and may not even have a fixed address
            print("Could not retrieve the address of the interface {} from the config".format(intf))
            print("You will need to update your DNS forwarding configuration manually")

    for addr in listen_addr:
        config.set(base + ['listen-address'], value=addr, replace=False)

    try:
        with open(file_name, 'w') as f:
            f.write(config.to_string())
    except OSError as e:
        print("Failed to save the modified config: {}".format(e))
        exit(1)

exit(0)