#!/usr/bin/env python3
#
# Copyright (C) 2018 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 time
import socket
import ipaddress

from vyos.config import Config
from vyos.util import ConfigError

config_file = r'/etc/ntp.conf'

def get_config():
    ntp = {}
    conf = Config()
    conf.set_level('system ntp')
    if not conf.exists(''):
        return ntp

    if conf.exists('allow-clients address'):
        ntp.setdefault('allow-networks', [])
        networks = []
        networks = conf.return_values('allow-clients address')
        for network in networks:
            ntp['allow-networks'].append(network)

    if conf.exists('server'):
        ntp.setdefault('servers', [])
        for node in conf.list_nodes('server'):
            server = {
                "name": node,
                "dynamic": False,
                "noselect": False,
                "preempt": False,
                "prefer": False,
            }
            if conf.exists('server {0} dynamic'.format(node)):
                server['dynamic'] = True
            if conf.exists('server {0} noselect'.format(node)):
                server['noselect'] = True
            if conf.exists('server {0} preempt'.format(node)):
                server['preempt'] = True
            if conf.exists('server {0} prefer'.format(node)):
                server['prefer'] = True

            ntp['servers'].append(server)

    return ntp

def verify(ntp):
    if 'allow-networks' in ntp.keys():
        for network in ntp['allow-networks']:
            try:
                addr = ipaddress.ip_network(network)
            except ValueError:
                raise ConfigError("{0} does not appear to be a valid IPv4 or IPv6 network, check host bits.".format(network))

    return None

def generate(ntp):
    config_header = '### Autogenerated by vyos-config-ntp.py on {tm} ###\n'.format(tm=time.strftime("%a, %d %b %Y %H:%M:%S", time.localtime()))

    # write new configuration file
    f = open(config_file, 'w')
    f.write(config_header)
    f.write('driftfile /var/lib/ntp/ntp.drift\n')
    f.write('# By default, only allow ntpd to query time sources, ignore any\n')
    f.write('# incoming requests.\n')
    f.write('restrict default ignore\n')
    f.write('\n')
    f.write('# Local users have unrestricted access, allowing reconfiguration\n')
    f.write('# via ntpdc\n')
    f.write('restrict 127.0.0.1\n')
    f.write('restrict -6 ::1\n')
    f.write('\n')

    if 'servers' in ntp.keys():
        for server in ntp['servers']:
            addr = socket.gethostbyname(server['name'])
            opt = ['dynamic', 'noselect', 'preempt', 'prefer']
            f.write('# Server configuration {0}\n'.format(server['name']))
            f.write('server {0} iburst {1}\n'.format(addr, '{0}'.format(' '.join(str(o) for o in opt if server[o]))))
            f.write('restrict {0} nomodify notrap nopeer noquery\n'.format(addr))
            f.write('\n')

    if 'allow-networks' in ntp.keys():
        for network in ntp['allow-networks']:
            addr = ipaddress.ip_network(network)
            f.write('# Client configuration: {0}\n'.format(network))
            f.write('restrict {0} mask {1} nomodify notrap nopeer\n'.format(addr.network_address, addr.netmask))
            f.write('\n')

    f.close()
    return None

def apply(ntp):
    if len(ntp) == 0:
        cmd = "sudo /usr/sbin/invoke-rc.d ntp stop"
    else:
        cmd = "sudo /usr/sbin/invoke-rc.d ntp force-reload"

    os.system(cmd)
    return None

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