#!/usr/bin/env python3
#
# Copyright (C) 2023 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 shutil import rmtree

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

load_balancing_dir = '/run/load-balance'
load_balancing_conf_file = f'{load_balancing_dir}/wlb.conf'
systemd_service = 'vyos-wan-load-balance.service'


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

    base = ['load-balancing', 'wan']
    lb = conf.get_config_dict(base, key_mangling=('-', '_'),
                              no_tag_node_value_mangle=True,
                              get_first_key=True,
                              with_recursive_defaults=True)

    # prune limit key if not set by user
    for rule in lb.get('rule', []):
        if lb.from_defaults(['rule', rule, 'limit']):
            del lb['rule'][rule]['limit']

    return lb


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

    if 'interface_health' not in lb:
        raise ConfigError(
            'A valid WAN load-balance configuration requires an interface with a nexthop!'
        )

    for interface, interface_config in lb['interface_health'].items():
        if 'nexthop' not in interface_config:
            raise ConfigError(
                f'interface-health {interface} nexthop must be specified!')

        if 'test' in interface_config:
            for test_rule, test_config in interface_config['test'].items():
                if 'type' in test_config:
                    if test_config['type'] == 'user-defined' and 'test_script' not in test_config:
                        raise ConfigError(
                            f'test {test_rule} script must be defined for test-script!'
                        )

    if 'rule' not in lb:
        Warning(
            'At least one rule with an (outbound) interface must be defined for WAN load balancing to be active!'
        )
    else:
        for rule, rule_config in lb['rule'].items():
            if 'inbound_interface' not in rule_config:
                raise ConfigError(f'rule {rule} inbound-interface must be specified!')
            if {'failover', 'exclude'} <= set(rule_config):
                raise ConfigError(f'rule {rule} failover cannot be configured with exclude!')
            if {'limit', 'exclude'} <= set(rule_config):
                raise ConfigError(f'rule {rule} limit cannot be used with exclude!')
            if 'interface' not in rule_config:
                if 'exclude' not in rule_config:
                    Warning(
                        f'rule {rule} will be inactive because no (outbound) interfaces have been defined for this rule'
                    )
            for direction in {'source', 'destination'}:
                if direction in rule_config:
                    if 'protocol' in rule_config and 'port' in rule_config[
                            direction]:
                        if rule_config['protocol'] not in {'tcp', 'udp'}:
                            raise ConfigError('ports can only be specified when protocol is "tcp" or "udp"')


def generate(lb):
    if not lb:
        # Delete /run/load-balance/wlb.conf
        if os.path.isfile(load_balancing_conf_file):
            os.unlink(load_balancing_conf_file)
        # Delete old directories
        if os.path.isdir(load_balancing_dir):
            rmtree(load_balancing_dir, ignore_errors=True)
        if os.path.exists('/var/run/load-balance/wlb.out'):
            os.unlink('/var/run/load-balance/wlb.out')

        return None

    # Create load-balance dir
    if not os.path.isdir(load_balancing_dir):
        os.mkdir(load_balancing_dir)

    render(load_balancing_conf_file, 'load-balancing/wlb.conf.j2', lb)

    return None


def apply(lb):
    if not lb:
        try:
            cmd(f'systemctl stop {systemd_service}')
        except Exception as e:
            print(f"Error message: {e}")

    else:
        cmd('sudo sysctl -w net.netfilter.nf_conntrack_acct=1')
        cmd(f'systemctl 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)