#!/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/>.

import os

from sys import exit
from copy import deepcopy

from vyos.config import Config
from vyos.ifconfig import L2TPv3If, Interface
from vyos import ConfigError
from netifaces import interfaces

default_config_data = {
    'address': [],
    'deleted': False,
    'description': '',
    'disable': False,
    'encapsulation': 'udp',
    'local_address': '',
    'local_port': 5000,
    'intf': '',
    'mtu': 1488,
    'peer_session_id': '',
    'peer_tunnel_id': '',
    'remote_address': '',
    'remote_port': 5000,
    'session_id': '',
    'tunnel_id': ''
}

def check_kmod():
    modules = ['l2tp_eth', 'l2tp_netlink', 'l2tp_ip', 'l2tp_ip6']
    for module in modules:
        if not os.path.exists(f'/sys/module/{module}'):
            if os.system(f'modprobe {module}') != 0:
                raise ConfigError(f'Loading Kernel module {module} failed')

def get_config():
    l2tpv3 = deepcopy(default_config_data)
    conf = Config()

    # determine tagNode instance
    if 'VYOS_TAGNODE_VALUE' not in os.environ:
        raise ConfigError('Interface (VYOS_TAGNODE_VALUE) not specified')

    l2tpv3['intf'] = os.environ['VYOS_TAGNODE_VALUE']

    # Check if interface has been removed
    if not conf.exists('interfaces l2tpv3 ' + l2tpv3['intf']):
        l2tpv3['deleted'] = True
        # to delete the l2tpv3 interface we need to current
        # tunnel_id and session_id
        if conf.exists_effective('interfaces l2tpv3 {} tunnel-id'.format(l2tpv3['intf'])):
            l2tpv3['tunnel_id'] = conf.return_effective_value(
                'interfaces l2tpv3 {} tunnel-id'.format(l2tpv3['intf']))

        if conf.exists_effective('interfaces l2tpv3 {} session-id'.format(l2tpv3['intf'])):
            l2tpv3['session_id'] = conf.return_effective_value(
                'interfaces l2tpv3 {} session-id'.format(l2tpv3['intf']))

        return l2tpv3

    # set new configuration level
    conf.set_level('interfaces l2tpv3 ' + l2tpv3['intf'])

    # retrieve configured interface addresses
    if conf.exists('address'):
        l2tpv3['address'] = conf.return_values('address')

    # retrieve interface description
    if conf.exists('description'):
        l2tpv3['description'] = conf.return_value('description')

    # get tunnel destination port
    if conf.exists('destination-port'):
        l2tpv3['remote_port'] = int(conf.return_value('destination-port'))

    # Disable this interface
    if conf.exists('disable'):
        l2tpv3['disable'] = True

    # get tunnel encapsulation type
    if conf.exists('encapsulation'):
        l2tpv3['encapsulation'] = conf.return_value('encapsulation')

    # get tunnel local ip address
    if conf.exists('local-ip'):
        l2tpv3['local_address'] = conf.return_value('local-ip')

    # Maximum Transmission Unit (MTU)
    if conf.exists('mtu'):
        l2tpv3['mtu'] = int(conf.return_value('mtu'))

    # Remote session id
    if conf.exists('peer-session-id'):
        l2tpv3['peer_session_id'] = conf.return_value('peer-session-id')

    # Remote tunnel id
    if conf.exists('peer-tunnel-id'):
        l2tpv3['peer_tunnel_id'] = conf.return_value('peer-tunnel-id')

    # Remote address of L2TPv3 tunnel
    if conf.exists('remote-ip'):
        l2tpv3['remote_address'] = conf.return_value('remote-ip')

    # Local session id
    if conf.exists('session-id'):
        l2tpv3['session_id'] = conf.return_value('session-id')

    # get local tunnel port
    if conf.exists('source-port'):
        l2tpv3['local_port'] = conf.return_value('source-port')

    # get local tunnel id
    if conf.exists('tunnel-id'):
        l2tpv3['tunnel_id'] = conf.return_value('tunnel-id')

    return l2tpv3


def verify(l2tpv3):
    if l2tpv3['deleted']:
        # bail out early
        return None

    if not l2tpv3['local_address']:
        raise ConfigError('Must configure the l2tpv3 local-ip for {}'.format(l2tpv3['intf']))

    if not l2tpv3['remote_address']:
        raise ConfigError('Must configure the l2tpv3 remote-ip for {}'.format(l2tpv3['intf']))

    if not l2tpv3['tunnel_id']:
        raise ConfigError('Must configure the l2tpv3 tunnel-id for {}'.format(l2tpv3['intf']))

    if not l2tpv3['peer_tunnel_id']:
        raise ConfigError('Must configure the l2tpv3 peer-tunnel-id for {}'.format(l2tpv3['intf']))

    if not l2tpv3['session_id']:
        raise ConfigError('Must configure the l2tpv3 session-id for {}'.format(l2tpv3['intf']))

    if not l2tpv3['peer_session_id']:
        raise ConfigError('Must configure the l2tpv3 peer-session-id for {}'.format(l2tpv3['intf']))

    return None


def generate(l2tpv3):
    return None

def apply(l2tpv3):
    # L2TPv3 interface needs to be created/deleted on-block, instead of
    # passing a ton of arguments, I just use a dict that is managed by
    # vyos.ifconfig
    conf = deepcopy(L2TPv3If.get_config())

    # Check if L2TPv3 interface already exists
    if l2tpv3['intf'] in interfaces():
        # L2TPv3 is picky when changing tunnels/sessions, thus we can simply
        # always delete it first.
        conf['session_id'] = l2tpv3['session_id']
        conf['tunnel_id'] = l2tpv3['tunnel_id']
        l = L2TPv3If(l2tpv3['intf'], **conf)
        l.remove()

    if not l2tpv3['deleted']:
        conf['peer_tunnel_id'] = l2tpv3['peer_tunnel_id']
        conf['local_port'] = l2tpv3['local_port']
        conf['remote_port'] = l2tpv3['remote_port']
        conf['encapsulation'] = l2tpv3['encapsulation']
        conf['local_address'] = l2tpv3['local_address']
        conf['remote_address'] = l2tpv3['remote_address']
        conf['session_id'] = l2tpv3['session_id']
        conf['tunnel_id'] = l2tpv3['tunnel_id']
        conf['peer_session_id'] = l2tpv3['peer_session_id']

        # Finally create the new interface
        l = L2TPv3If(l2tpv3['intf'], **conf)
        # update interface description used e.g. by SNMP
        l.set_alias(l2tpv3['description'])
        # Maximum Transfer Unit (MTU)
        l.set_mtu(l2tpv3['mtu'])

        # Configure interface address(es) - no need to implicitly delete the
        # old addresses as they have already been removed by deleting the
        # interface above
        for addr in l2tpv3['address']:
            l.add_addr(addr)

        # As the interface is always disabled first when changing parameters
        # we will only re-enable the interface if it is not  administratively
        # disabled
        if not l2tpv3['disable']:
            l.set_state('up')

    return None

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