#!/usr/bin/env python3
#
# Copyright (C) 2019-2020 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
import re

from copy import deepcopy
from socket import AF_INET, SOCK_STREAM, socket
from sys import exit
from time import sleep

from jinja2 import FileSystemLoader, Environment

from vyos.config import Config
from vyos.defaults import directories as vyos_data_dir
from vyos import ConfigError
from vyos.util import run


pidfile = r'/var/run/accel_l2tp.pid'
l2tp_cnf_dir = r'/etc/accel-ppp/l2tp'
chap_secrets = l2tp_cnf_dir + '/chap-secrets'
l2tp_conf = l2tp_cnf_dir + '/l2tp.config'
# accel-pppd -d -c /etc/accel-ppp/l2tp/l2tp.config -p /var/run/accel_l2tp.pid

# config path creation
if not os.path.exists(l2tp_cnf_dir):
    os.makedirs(l2tp_cnf_dir)


default_config_data = {
    'authentication': {
        'mode': 'local',
        'local-users': {
        },
        'radiussrv': {},
        'radiusopt': {},
        'auth_proto': [],
        'mppe': 'prefer'
    },
    'outside_addr': '',
    'gateway_address': '10.255.255.0',
    'dns': [],
    'dnsv6': [],
    'wins': [],
    'client_ip_pool': None,
    'client_ip_subnets': [],
    'client_ipv6_pool': {},
    'mtu': '1436',
    'ip6_column': '',
    'ip6_dp_column': '',
    'ppp_options': {},
}

###
# inline helper functions
###
# depending on hw and threads, daemon needs a little to start
# if it takes longer than 100 * 0.5 secs, exception is being raised
# not sure if that's the best way to check it, but it worked so far quite well
###


def chk_con():
    cnt = 0
    s = socket(AF_INET, SOCK_STREAM)
    while True:
        try:
            s.connect(("127.0.0.1", 2004))
            break
        except ConnectionRefusedError:
            sleep(0.5)
            cnt += 1
            if cnt == 100:
                raise("failed to start l2tp server")
                break


def _accel_cmd(command):
  return run(f'/usr/bin/accel-cmd -p 2004 {command}')

###
# inline helper functions end
###


def get_config():
    c = Config()
    base = ['vpn', 'l2tp' 'remote-access']
    if not c.exists(base):
        return None

    c.set_level(base)
    config_data = deepcopy(default_config_data)

    ### general options ###
    if c.exists('dns-servers server-1'):
        config_data['dns'].append(c.return_value('dns-servers server-1'))
    if c.exists('dns-servers server-2'):
        config_data['dns'].append(c.return_value('dns-servers server-2'))
    if c.exists('dnsv6-servers'):
        for dns6_server in c.return_values('dnsv6-servers'):
            config_data['dnsv6'].append(dns6_server)
    if c.exists('wins-servers server-1'):
        config_data['wins'].append(c.return_value('wins-servers server-1'))
    if c.exists('wins-servers server-2'):
        config_data['wins'].append(c.return_value('wins-servers server-2'))
    if c.exists('outside-address'):
        config_data['outside_addr'] = c.return_value('outside-address')

    # auth local
    if c.exists('authentication mode local'):
        if c.exists('authentication local-users username'):
            for usr in c.list_nodes('authentication local-users username'):
                config_data['authentication']['local-users'].update(
                    {
                        usr: {
                            'passwd': '',
                            'state': 'enabled',
                            'ip': '*',
                            'upload': None,
                            'download': None
                        }
                    }
                )

                if c.exists('authentication local-users username ' + usr + ' password'):
                    config_data['authentication']['local-users'][usr]['passwd'] = c.return_value(
                        'authentication local-users username ' + usr + ' password')
                if c.exists('authentication local-users username ' + usr + ' disable'):
                    config_data['authentication']['local-users'][usr]['state'] = 'disable'
                if c.exists('authentication local-users username ' + usr + ' static-ip'):
                    config_data['authentication']['local-users'][usr]['ip'] = c.return_value(
                        'authentication local-users username ' + usr + ' static-ip')
                if c.exists('authentication local-users username ' + usr + ' rate-limit download'):
                    config_data['authentication']['local-users'][usr]['download'] = c.return_value(
                        'authentication local-users username ' + usr + ' rate-limit download')
                if c.exists('authentication local-users username ' + usr + ' rate-limit upload'):
                    config_data['authentication']['local-users'][usr]['upload'] = c.return_value(
                        'authentication local-users username ' + usr + ' rate-limit upload')

    # authentication mode radius servers and settings

    if c.exists('authentication mode radius'):
        config_data['authentication']['mode'] = 'radius'
        rsrvs = c.list_nodes('authentication radius server')
        for rsrv in rsrvs:
            if c.return_value('authentication radius server ' + rsrv + ' fail-time') == None:
                ftime = '0'
            else:
                ftime = str(c.return_value(
                    'authentication radius server ' + rsrv + ' fail-time'))
            if c.return_value('authentication radius-server ' + rsrv + ' req-limit') == None:
                reql = '0'
            else:
                reql = str(c.return_value(
                    'authentication radius server ' + rsrv + ' req-limit'))

            config_data['authentication']['radiussrv'].update(
                {
                    rsrv: {
                        'secret': c.return_value('authentication radius server ' + rsrv + ' key'),
                        'fail-time': ftime,
                        'req-limit': reql
                    }
                }
            )
        # Source ip address feature
        if c.exists('authentication radius source-address'):
            config_data['authentication']['radius_source_address'] = c.return_value(
                'authentication radius source-address')

        # advanced radius-setting
        if c.exists('authentication radius acct-timeout'):
            config_data['authentication']['radiusopt']['acct-timeout'] = c.return_value(
                'authentication radius acct-timeout')
        if c.exists('authentication radius max-try'):
            config_data['authentication']['radiusopt']['max-try'] = c.return_value(
                'authentication radius max-try')
        if c.exists('authentication radius timeout'):
            config_data['authentication']['radiusopt']['timeout'] = c.return_value(
                'authentication radius timeout')
        if c.exists('authentication radius nas-identifier'):
            config_data['authentication']['radiusopt']['nas-id'] = c.return_value(
                'authentication radius nas-identifier')
        if c.exists('authentication radius dae-server'):
            # Set default dae-server port if not defined
            if c.exists('authentication radius dae-server port'):
                dae_server_port = c.return_value(
                    'authentication radius dae-server port')
            else:
                dae_server_port = "3799"
            config_data['authentication']['radiusopt'].update(
                {
                    'dae-srv': {
                        'ip-addr': c.return_value('authentication radius dae-server ip-address'),
                        'port': dae_server_port,
                        'secret': str(c.return_value('authentication radius dae-server secret'))
                    }
                }
            )
        # filter-id is the internal accel default if attribute is empty
        # set here as default for visibility which may change in the future
        if c.exists('authentication radius rate-limit enable'):
            if not c.exists('authentication radius rate-limit attribute'):
                config_data['authentication']['radiusopt']['shaper'] = {
                    'attr': 'Filter-Id'
                }
            else:
                config_data['authentication']['radiusopt']['shaper'] = {
                    'attr': c.return_value('authentication radius rate-limit attribute')
                }
            if c.exists('authentication radius rate-limit vendor'):
                config_data['authentication']['radiusopt']['shaper']['vendor'] = c.return_value(
                    'authentication radius rate-limit vendor')

    if c.exists('client-ip-pool'):
        if c.exists('client-ip-pool start') and c.exists('client-ip-pool stop'):
            config_data['client_ip_pool'] = c.return_value(
                'client-ip-pool start') + '-' + re.search('[0-9]+$', c.return_value('client-ip-pool stop')).group(0)

    if c.exists('client-ip-pool subnet'):
        config_data['client_ip_subnets'] = c.return_values(
            'client-ip-pool subnet')

    if c.exists('client-ipv6-pool prefix'):
        config_data['client_ipv6_pool']['prefix'] = c.return_values(
            'client-ipv6-pool prefix')
        config_data['ip6_column'] = 'ip6,'
    if c.exists('client-ipv6-pool delegate-prefix'):
        config_data['client_ipv6_pool']['delegate_prefix'] = c.return_values(
            'client-ipv6-pool delegate-prefix')
        config_data['ip6_dp_column'] = 'ip6-dp,'

    if c.exists('mtu'):
        config_data['mtu'] = c.return_value('mtu')

    # gateway address
    if c.exists('gateway-address'):
        config_data['gateway_address'] = c.return_value('gateway-address')
    else:
        # calculate gw-ip-address
        if c.exists('client-ip-pool start'):
            # use start ip as gw-ip-address
            config_data['gateway_address'] = c.return_value(
                'client-ip-pool start')
        elif c.exists('client-ip-pool subnet'):
            # use first ip address from first defined pool
            lst_ip = re.findall("\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}", c.return_values(
                'client-ip-pool subnet')[0])
            config_data['gateway_address'] = lst_ip[0]

    if c.exists('authentication require'):
        auth_mods = {'pap': 'pap', 'chap': 'auth_chap_md5',
                     'mschap': 'auth_mschap_v1', 'mschap-v2': 'auth_mschap_v2'}
        for proto in c.return_values('authentication require'):
            config_data['authentication']['auth_proto'].append(
                auth_mods[proto])
    else:
        config_data['authentication']['auth_proto'] = ['auth_mschap_v2']

    if c.exists('authentication mppe'):
        config_data['authentication']['mppe'] = c.return_value(
            'authentication mppe')

    if c.exists('idle'):
        config_data['idle_timeout'] = c.return_value('idle')

    # LNS secret
    if c.exists('lns shared-secret'):
        config_data['lns_shared_secret'] = c.return_value('lns shared-secret')

    if c.exists('ccp-disable'):
        config_data['ccp_disable'] = True

    # ppp_options
    ppp_options = {}
    if c.exists('ppp-options'):
        if c.exists('ppp-options lcp-echo-failure'):
            ppp_options['lcp-echo-failure'] = c.return_value(
                'ppp-options lcp-echo-failure')
        if c.exists('ppp-options lcp-echo-interval'):
            ppp_options['lcp-echo-interval'] = c.return_value(
                'ppp-options lcp-echo-interval')

    if len(ppp_options) != 0:
        config_data['ppp_options'] = ppp_options

    return config_data


def verify(c):
    if c == None:
        return None

    if c['authentication']['mode'] == 'local':
        if not c['authentication']['local-users']:
            raise ConfigError(
                'l2tp-server authentication local-users required')
        for usr in c['authentication']['local-users']:
            if not c['authentication']['local-users'][usr]['passwd']:
                raise ConfigError('user ' + usr + ' requires a password')

    if c['authentication']['mode'] == 'radius':
        if len(c['authentication']['radiussrv']) == 0:
            raise ConfigError('radius server required')
        for rsrv in c['authentication']['radiussrv']:
            if c['authentication']['radiussrv'][rsrv]['secret'] == None:
                raise ConfigError('radius server ' + rsrv +
                                  ' needs a secret configured')

    # check for the existence of a client ip pool
    if not c['client_ip_pool'] and not c['client_ip_subnets']:
        raise ConfigError(
            "set vpn l2tp remote-access client-ip-pool requires subnet or start/stop IP pool")

    # check ipv6
    if 'delegate_prefix' in c['client_ipv6_pool'] and not 'prefix' in c['client_ipv6_pool']:
        raise ConfigError(
            "\"set vpn l2tp remote-access client-ipv6-pool prefix\" required for delegate-prefix ")

    if len(c['dnsv6']) > 3:
        raise ConfigError("Maximum allowed dnsv6-servers addresses is 3")


def generate(c):
    if c == None:
        return None

    # Prepare Jinja2 template loader from files
    tmpl_path = os.path.join(vyos_data_dir['data'], 'templates', 'l2tp')
    fs_loader = FileSystemLoader(tmpl_path)
    env = Environment(loader=fs_loader, trim_blocks=True)

    # accel-cmd reload doesn't work so any change results in a restart of the daemon
    try:
        if os.cpu_count() == 1:
            c['thread_cnt'] = 1
        else:
            c['thread_cnt'] = int(os.cpu_count()/2)
    except KeyError:
        if os.cpu_count() == 1:
            c['thread_cnt'] = 1
        else:
            c['thread_cnt'] = int(os.cpu_count()/2)

    tmpl = env.get_template('l2tp.config.tmpl')
    config_text = tmpl.render(c)
    open(l2tp_conf, 'w').write(config_text)

    if c['authentication']['local-users']:
        tmpl = env.get_template('chap-secrets.tmpl')
        chap_secrets_txt = tmpl.render(c)
        old_umask = os.umask(0o077)
        open(chap_secrets, 'w').write(chap_secrets_txt)
        os.umask(old_umask)

    return c


def apply(c):
    if c == None:
        if os.path.exists(pidfile):
            _accel_cmd('shutdown hard')
            if os.path.exists(pidfile):
                os.remove(pidfile)
        return None

    if not os.path.exists(pidfile):
        ret = run(f'/usr/sbin/accel-pppd -c {l2tp_conf} -p {pidfile} -d')
        chk_con()
        if ret != 0 and os.path.exists(pidfile):
            os.remove(pidfile)
            raise ConfigError('accel-pppd failed to start')
    else:
        # if gw ip changes, only restart doesn't work
        _accel_cmd('restart')


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