#!/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/>.
#
#

"""
conf-mode script for 'system host-name' and 'system domain-name'.
"""

import os
import re
import sys
import subprocess
import copy
import jinja2
import glob

from vyos.config import Config
from vyos import ConfigError

config_file_hosts = '/etc/hosts'
config_file_resolv = '/etc/resolv.conf'

config_tmpl_hosts = """
### Autogenerated by host_name.py ###
127.0.0.1       localhost {{ hostname }}{% if domain_name %}.{{ domain_name }}{% endif %}

# The following lines are desirable for IPv6 capable hosts
::1             localhost ip6-localhost ip6-loopback
fe00::0         ip6-localnet
ff00::0         ip6-mcastprefix
ff02::1         ip6-allnodes
ff02::2         ip6-allrouters

### modifications from other scripts should be added below


"""

config_tmpl_resolv = """
### Autogenerated by host_name.py ###
{% for ns in nameserver -%}
nameserver {{ ns }}
{% endfor -%}

{%- if domain_name %}
domain {{ domain_name }}
{%- endif %}

{%- if domain_search %}
search {{ domain_search | join(" ") }}
{%- endif %}

"""

# borrowed from: https://github.com/donjajo/py-world/blob/master/resolvconfReader.py, THX!
def get_resolvers(file):
    resolvers = []
    try:
        with open(file, 'r') as resolvconf:
            for line in resolvconf.readlines():
                line = line.split('#',1)[0];
                line = line.rstrip();
                if 'nameserver' in line:
                    resolvers.append(line.split()[1])
        return resolvers
    except IOError:
        return []

default_config_data = {
    'hostname': 'vyos',
    'domain_name': '',
    'domain_search': [],
    'nameserver': [],
    'no_dhcp_ns': False
}

def get_config():
    conf = Config()
    hosts = copy.deepcopy(default_config_data)

    hosts['hostname'] = conf.return_value("system host-name")
    hosts['domain_name'] = conf.return_value("system domain-name")

    if hosts['domain_name']:
        hosts['domain_search'].append(hosts['domain_name'])

    for search in conf.return_values("system domain-search domain"):
        hosts['domain_search'].append(search)

    hosts['nameserver'] = conf.return_values("system name-server")
    hosts['no_dhcp_ns'] = conf.exists('system disable-dhcp-nameservers')

    return hosts

def verify(config):
    if config is None:
        return None

    # pattern $VAR(@) "^[[:alnum:]][-.[:alnum:]]*[[:alnum:]]$" ; "invalid host name $VAR(@)"
    hostname_regex = re.compile("^[A-Za-z0-9][-.A-Za-z0-9]*[A-Za-z0-9]$")
    if not hostname_regex.match(config['hostname']):
        raise ConfigError('Invalid host name ' + config["hostname"])

    # pattern $VAR(@) "^.{1,63}$" ; "invalid host-name length"
    length = len(config['hostname'])
    if length < 1 or length > 63:
        raise ConfigError(
            'Invalid host-name length, must be less than 63 characters')

    # The search list is currently limited to six domains with a total of 256 characters.
    # https://linux.die.net/man/5/resolv.conf
    if len(config['domain_search']) > 6:
        raise ConfigError('The search list is currently limited to six domains')

    tmp = ' '.join(config['domain_search'])
    if len(tmp) > 256:
        raise ConfigError('The search list is currently limited to 256 characters')

    return None

def generate(config):
    if config is None:
        return None

    # If "system disable-dhcp-nameservers" is __configured__ all DNS resolvers
    # received via dhclient should not be added into the final 'resolv.conf'.
    #
    # We iterate over every resolver file and retrieve the received nameservers
    # for later adjustment of the system nameservers
    dhcp_ns = []
    for file in glob.glob('/etc/resolv.conf.dhclient-new*'):
        for r in get_resolvers(file):
            dhcp_ns.append(r)

    if not config['no_dhcp_ns']:
        config['nameserver'] += dhcp_ns

    # We have third party scripts altering /etc/hosts, too.
    # One example are the DHCP hostname update scripts thus we need to cache in
    # every modification first - so changing domain-name, domain-search or hostname
    # during runtime works
    old_hosts = ""
    with open(config_file_hosts, 'r') as f:
        # Skips text before the beginning of our marker.
        # NOTE: Marker __MUST__ match the one specified in config_tmpl_hosts
        for line in f:
            if line.strip() == '### modifications from other scripts should be added below':
                break

        for line in f:
            # This additional line.strip() filters empty lines
            if line.strip():
                old_hosts += line

    # Add an additional newline
    old_hosts += '\n'

    tmpl = jinja2.Template(config_tmpl_hosts)
    config_text = tmpl.render(config)
    with open(config_file_hosts, 'w') as f:
        f.write(config_text)
        f.write(old_hosts)

    tmpl = jinja2.Template(config_tmpl_resolv)
    config_text = tmpl.render(config)
    with open(config_file_resolv, 'w') as f:
        f.write(config_text)

    return None

def apply(config):
    if config is None:
        return None

    fqdn = config['hostname']
    if config['domain_name']:
        fqdn += '.' + config['domain_name']

    os.system("hostnamectl set-hostname --static {0}".format(fqdn))

    # Restart services that use the hostname
    os.system("systemctl restart rsyslog.service")

    # If SNMP is running, restart it too
    if os.system("pgrep snmpd > /dev/null") == 0:
        os.system("systemctl restart snmpd.service")

    return None

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