#!/usr/bin/env python3
#
# Copyright (C) 2020-2021 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 jmespath
import json
import os

from sys import exit
from netifaces import interfaces

from vyos.base import Warning
from vyos.config import Config
from vyos.template import render
from vyos.utils.process import cmd
from vyos.utils.kernel import check_kmod
from vyos.utils.dict import dict_search
from vyos.template import is_ipv6
from vyos import ConfigError
from vyos import airbag
airbag.enable()

k_mod = ['nft_nat', 'nft_chain_nat']

nftables_nat66_config = '/run/nftables_nat66.nft'
ndppd_config = '/run/ndppd/ndppd.conf'

def get_handler(json, chain, target):
    """ Get nftable rule handler number of given chain/target combination.
    Handler is required when adding NAT66/Conntrack helper targets """
    for x in json:
        if x['chain'] != chain:
            continue
        if x['target'] != target:
            continue
        return x['handle']

    return None

def get_config(config=None):
    if config:
        conf = config
    else:
        conf = Config()

    base = ['nat66']
    nat = conf.get_config_dict(base, key_mangling=('-', '_'), get_first_key=True)

    # read in current nftable (once) for further processing
    tmp = cmd('nft -j list table ip6 raw')
    nftable_json = json.loads(tmp)

    # condense the full JSON table into a list with only relevand informations
    pattern = 'nftables[?rule].rule[?expr[].jump].{chain: chain, handle: handle, target: expr[].jump.target | [0]}'
    condensed_json = jmespath.search(pattern, nftable_json)

    if not conf.exists(base):
        nat['helper_functions'] = 'remove'
        nat['pre_ct_ignore'] = get_handler(condensed_json, 'PREROUTING', 'VYOS_CT_HELPER')
        nat['pre_ct_conntrack'] = get_handler(condensed_json, 'PREROUTING', 'NAT_CONNTRACK')
        nat['out_ct_ignore'] = get_handler(condensed_json, 'OUTPUT', 'VYOS_CT_HELPER')
        nat['out_ct_conntrack'] = get_handler(condensed_json, 'OUTPUT', 'NAT_CONNTRACK')
        nat['deleted'] = ''
        return nat

    # check if NAT66 connection tracking helpers need to be set up - this has to
    # be done only once
    if not get_handler(condensed_json, 'PREROUTING', 'NAT_CONNTRACK'):
        nat['helper_functions'] = 'add'

        # Retrieve current table handler positions
        nat['pre_ct_ignore'] = get_handler(condensed_json, 'PREROUTING', 'VYOS_CT_IGNORE')
        nat['pre_ct_conntrack'] = get_handler(condensed_json, 'PREROUTING', 'VYOS_CT_PREROUTING_HOOK')
        nat['out_ct_ignore'] = get_handler(condensed_json, 'OUTPUT', 'VYOS_CT_IGNORE')
        nat['out_ct_conntrack'] = get_handler(condensed_json, 'OUTPUT', 'VYOS_CT_OUTPUT_HOOK')
    else:
        nat['helper_functions'] = 'has'

    return nat

def verify(nat):
    if not nat or 'deleted' in nat:
        # no need to verify the CLI as NAT66 is going to be deactivated
        return None

    if 'helper_functions' in nat and nat['helper_functions'] != 'has':
        if not (nat['pre_ct_conntrack'] or nat['out_ct_conntrack']):
            raise Exception('could not determine nftable ruleset handlers')

    if dict_search('source.rule', nat):
        for rule, config in dict_search('source.rule', nat).items():
            err_msg = f'Source NAT66 configuration error in rule {rule}:'
            if 'outbound_interface' not in config:
                raise ConfigError(f'{err_msg} outbound-interface not specified')

            if config['outbound_interface'] not in interfaces():
                raise ConfigError(f'rule "{rule}" interface "{config["outbound_interface"]}" does not exist on this system')

            addr = dict_search('translation.address', config)
            if addr != None:
                if addr != 'masquerade' and not is_ipv6(addr):
                    raise ConfigError(f'IPv6 address {addr} is not a valid address')
            else:
                if 'exclude' not in config:
                    raise ConfigError(f'{err_msg} translation address not specified')

            prefix = dict_search('source.prefix', config)
            if prefix != None:
                if not is_ipv6(prefix):
                    raise ConfigError(f'{err_msg} source-prefix not specified')

    if dict_search('destination.rule', nat):
        for rule, config in dict_search('destination.rule', nat).items():
            err_msg = f'Destination NAT66 configuration error in rule {rule}:'

            if 'inbound_interface' not in config:
                raise ConfigError(f'{err_msg}\n' \
                                  'inbound-interface not specified')
            else:
                if config['inbound_interface'] not in 'any' and config['inbound_interface'] not in interfaces():
                    Warning(f'rule "{rule}" interface "{config["inbound_interface"]}" does not exist on this system')

    return None

def generate(nat):
    if not os.path.exists(nftables_nat66_config):
        nat['first_install'] = True

    render(nftables_nat66_config, 'firewall/nftables-nat66.j2', nat, permission=0o755)
    render(ndppd_config, 'ndppd/ndppd.conf.j2', nat, permission=0o755)
    return None

def apply(nat):
    if not nat:
        return None

    cmd(f'nft -f {nftables_nat66_config}')

    if 'deleted' in nat or not dict_search('source.rule', nat):
        cmd('systemctl stop ndppd')
        if os.path.isfile(ndppd_config):
            os.unlink(ndppd_config)
    else:
        cmd('systemctl restart ndppd')

    return None

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