#!/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 sys
import os
import re
import subprocess
import socket
import time

from jinja2 import FileSystemLoader, Environment

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

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)

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

def accel_cmd(cmd=''):
  if not cmd:
    return None
  try:
    ret = subprocess.check_output(['/usr/bin/accel-cmd','-p','2004',cmd]).decode().strip()
    return ret
  except:
    return 1

###
# inline helper functions end
###

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

  c.set_level('vpn l2tp remote-access')
  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'         : {},
  }

  ### 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)

  ### 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 = subprocess.call(['/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)
    sys.exit(1)