#!/usr/bin/env python3
#
# Copyright (C) 2018-2020 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

from netifaces import interfaces
from sys import exit

from vyos.config import Config
from vyos import ConfigError
from vyos.util import call
from vyos.template import render

from vyos import airbag
airbag.enable()

config_file = r'/etc/ssh/sshd_config'
systemd_override = r'/etc/systemd/system/ssh.service.d/override.conf'

default_config_data = {
    'port' : '22',
    'log_level': 'INFO',
    'password_authentication': 'yes',
    'host_validation': 'yes',
    'vrf': ''
}

def get_config():
    ssh = default_config_data
    conf = Config()
    base = ['service', 'ssh']
    if not conf.exists(base):
        return None
    else:
        conf.set_level(base)

    tmp = ['access-control', 'allow', 'user']
    if conf.exists(tmp):
        ssh['allow_users'] = conf.return_values(tmp)

    tmp = ['access-control', 'allow', 'group']
    if conf.exists(tmp):
        ssh['allow_groups'] = conf.return_values(tmp)

    tmp = ['access-control', 'deny' 'user']
    if conf.exists(tmp):
        ssh['deny_users'] = conf.return_values(tmp)

    tmp = ['access-control', 'deny', 'group']
    if conf.exists(tmp):
        ssh['deny_groups'] = conf.return_values(tmp)

    tmp = ['ciphers']
    if conf.exists(tmp):
        ssh['ciphers'] = conf.return_values(tmp)

    tmp = ['key-exchange']
    if conf.exists(tmp):
        ssh['key_exchange'] = conf.return_values(tmp)

    if conf.exists(['disable-host-validation']):
        ssh['host_validation'] = 'no'

    if conf.exists(['disable-password-authentication']):
        ssh['password_authentication'] = 'no'

    tmp = ['listen-address']
    if conf.exists(tmp):
        # We can listen on both IPv4 and IPv6 addresses
        # Maybe there could be a check in the future if the configured IP address
        # is configured on this system at all?
        ssh['listen_on'] = conf.return_values(tmp)

    tmp = ['loglevel']
    if conf.exists(tmp):
        ssh['log_level'] = conf.return_value(tmp)

    tmp = ['mac']
    if conf.exists(tmp):
        ssh['mac'] = conf.return_values(tmp)

    tmp = ['port']
    if conf.exists(tmp):
        ssh['port'] = conf.return_values(tmp)

    tmp = ['client-keepalive-interval']
    if conf.exists(tmp):
        ssh['client_keepalive'] = conf.return_value(tmp)

    tmp = ['vrf']
    if conf.exists(tmp):
        ssh['vrf'] = conf.return_value(tmp)

    return ssh

def verify(ssh):
    if not ssh:
        return None

    if 'loglevel' in ssh.keys():
        allowed_loglevel = 'QUIET, FATAL, ERROR, INFO, VERBOSE'
        if not ssh['loglevel'] in allowed_loglevel:
            raise ConfigError('loglevel must be one of "{0}"\n'.format(allowed_loglevel))

    if ssh['vrf'] and ssh['vrf'] not in interfaces():
        raise ConfigError('VRF "{vrf}" does not exist'.format(**ssh))

    return None

def generate(ssh):
    if not ssh:
        return None

    render(config_file, 'ssh/sshd_config.tmpl', ssh, trim_blocks=True)
    render(systemd_override, 'ssh/override.conf.tmpl', ssh, trim_blocks=True)

    return None

def apply(ssh):
    if not ssh:
        # SSH access is removed in the commit
        call('systemctl stop ssh.service')
        if os.path.isfile(config_file):
            os.unlink(config_file)
        if os.path.isfile(systemd_override):
            os.unlink(systemd_override)
    else:
        # Reload systemd manager configuration
        call('systemctl daemon-reload')
        call('systemctl restart ssh.service')

    return None

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