# Copyright 2014 OpenStack Foundation
# All Rights Reserved.
#
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

import os
import pwd

from itertools import chain as iter_chain

import jinja2
import netaddr
from neutron_lib import constants
from neutron_lib.utils import file as file_utils
from oslo_log import log as logging
import six

from neutron.agent.linux import external_process
from neutron.agent.linux import utils

RADVD_SERVICE_NAME = 'radvd'
RADVD_SERVICE_CMD = 'radvd'
# We can configure max of 3 DNS servers in radvd RDNSS section.
MAX_RDNSS_ENTRIES = 3

LOG = logging.getLogger(__name__)


CONFIG_TEMPLATE = jinja2.Template("""interface {{ interface_name }}
{
   AdvSendAdvert on;
   MinRtrAdvInterval {{ min_rtr_adv_interval }};
   MaxRtrAdvInterval {{ max_rtr_adv_interval }};

   {% if network_mtu >= constants.IPV6_MIN_MTU %}
   AdvLinkMTU {{network_mtu}};
   {% endif %}

   {% if constants.DHCPV6_STATELESS in ra_modes %}
   AdvOtherConfigFlag on;
   {% endif %}

   {% if constants.DHCPV6_STATEFUL in ra_modes %}
   AdvManagedFlag on;
   {% endif %}

   {% if dns_servers %}
   RDNSS {% for dns in dns_servers %} {{ dns }} {% endfor %} {};
   {% endif %}

   {% for prefix in auto_config_prefixes %}
   prefix {{ prefix }}
   {
        AdvOnLink on;
        AdvAutonomous on;
   };
   {% endfor %}

   {% for prefix in stateful_config_prefixes %}
   prefix {{ prefix }}
   {
        AdvOnLink on;
        AdvAutonomous off;
   };
   {% endfor %}
};
""")


class DaemonMonitor(object):
    """Manage the data and state of an radvd process."""

    def __init__(self, router_id, router_ns, process_monitor, dev_name_helper,
                 agent_conf):
        self._router_id = router_id
        self._router_ns = router_ns
        self._process_monitor = process_monitor
        self._dev_name_helper = dev_name_helper
        self._agent_conf = agent_conf

    def _generate_radvd_conf(self, router_ports):
        radvd_conf = utils.get_conf_file_name(self._agent_conf.ra_confs,
                                              self._router_id,
                                              'radvd.conf',
                                              True)
        buf = six.StringIO()
        for p in router_ports:
            subnets = p.get('subnets', [])
            v6_subnets = [subnet for subnet in subnets if
                          netaddr.IPNetwork(subnet['cidr']).version == 6]
            if not v6_subnets:
                continue
            ra_modes = {subnet['ipv6_ra_mode'] for subnet in v6_subnets}
            auto_config_prefixes = [
                subnet['cidr'] for subnet in v6_subnets
                if (subnet['ipv6_ra_mode'] == constants.IPV6_SLAAC or
                    subnet['ipv6_ra_mode'] == constants.DHCPV6_STATELESS)
            ]
            stateful_config_prefixes = [
                subnet['cidr'] for subnet in v6_subnets
                if subnet['ipv6_ra_mode'] == constants.DHCPV6_STATEFUL
            ]
            interface_name = self._dev_name_helper(p['id'])
            slaac_subnets = [
                subnet for subnet in v6_subnets
                if subnet['ipv6_ra_mode'] == constants.IPV6_SLAAC
            ]
            dns_servers = list(iter_chain(*[
                subnet['dns_nameservers'] for subnet in slaac_subnets
                if subnet.get('dns_nameservers')
            ]))
            network_mtu = p.get('mtu', 0)

            buf.write('%s' % CONFIG_TEMPLATE.render(
                ra_modes=list(ra_modes),
                interface_name=interface_name,
                auto_config_prefixes=auto_config_prefixes,
                stateful_config_prefixes=stateful_config_prefixes,
                dns_servers=dns_servers[0:MAX_RDNSS_ENTRIES],
                n_const=constants,
                constants=constants,
                min_rtr_adv_interval=self._agent_conf.min_rtr_adv_interval,
                max_rtr_adv_interval=self._agent_conf.max_rtr_adv_interval,
                network_mtu=int(network_mtu)))

        contents = buf.getvalue()
        LOG.debug("radvd config = %s", contents)
        # radvd conf file can't be writeable by self/group
        file_utils.replace_file(radvd_conf, contents, file_mode=0o444)
        return radvd_conf

    def _get_radvd_process_manager(self, callback=None):
        return external_process.ProcessManager(
            uuid=self._router_id,
            default_cmd_callback=callback,
            namespace=self._router_ns,
            service=RADVD_SERVICE_NAME,
            conf=self._agent_conf,
            run_as_root=True)

    def _spawn_radvd(self, radvd_conf):
        def callback(pid_file):
            # drop radvd daemon privileges and run as the neutron user
            radvd_user = pwd.getpwuid(os.geteuid()).pw_name
            # we need to use -m syslog and f.e. not -m stderr (the default)
            # or -m stderr_syslog so that radvd 2.0+ will close stderr and
            # exit after daemonization; otherwise, the current thread will
            # be locked waiting for result from radvd that won't ever come
            # until the process dies
            radvd_cmd = [RADVD_SERVICE_CMD,
                         '-C', '%s' % radvd_conf,
                         '-p', '%s' % pid_file,
                         '-u', '%s' % radvd_user,
                         '-m', 'syslog']
            return radvd_cmd

        pm = self._get_radvd_process_manager(callback)
        pm.enable(reload_cfg=True)
        self._process_monitor.register(uuid=self._router_id,
                                       service_name=RADVD_SERVICE_NAME,
                                       monitored_process=pm)
        LOG.debug("radvd enabled for router %s", self._router_id)

    def enable(self, router_ports):
        for p in router_ports:
            for subnet in p['subnets']:
                if netaddr.IPNetwork(subnet['cidr']).version == 6:
                    LOG.debug("Enable IPv6 RA for router %s", self._router_id)
                    radvd_conf = self._generate_radvd_conf(router_ports)
                    self._spawn_radvd(radvd_conf)
                    return

        # Kill the daemon if it's running
        self.disable()

    def disable(self):
        self._process_monitor.unregister(uuid=self._router_id,
                                         service_name=RADVD_SERVICE_NAME)
        pm = self._get_radvd_process_manager()
        pm.disable()
        utils.remove_conf_files(self._agent_conf.ra_confs, self._router_id)
        LOG.debug("radvd disabled for router %s", self._router_id)

    @property
    def enabled(self):
        return self._get_radvd_process_manager().active