# vim: tabstop=4 shiftwidth=4 softtabstop=4

# Copyright 2012 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 abc
import os
import re
import shutil
import socket
import StringIO
import sys

import netaddr
from oslo.config import cfg

from neutron.agent.linux import ip_lib
from neutron.agent.linux import utils
from neutron.openstack.common import jsonutils
from neutron.openstack.common import log as logging
from neutron.openstack.common import uuidutils

LOG = logging.getLogger(__name__)

OPTS = [
    cfg.StrOpt('dhcp_confs',
               default='$state_path/dhcp',
               help=_('Location to store DHCP server config files')),
    cfg.StrOpt('dhcp_domain',
               default='openstacklocal',
               help=_('Domain to use for building the hostnames')),
    cfg.StrOpt('dnsmasq_config_file',
               default='',
               help=_('Override the default dnsmasq settings with this file')),
    cfg.StrOpt('dnsmasq_dns_server',
               help=_('Use another DNS server before any in '
                      '/etc/resolv.conf.')),
]

IPV4 = 4
IPV6 = 6
UDP = 'udp'
TCP = 'tcp'
DNS_PORT = 53
DHCPV4_PORT = 67
DHCPV6_PORT = 547
METADATA_DEFAULT_IP = '169.254.169.254'
WIN2k3_STATIC_DNS = 249


class DhcpBase(object):
    __metaclass__ = abc.ABCMeta

    def __init__(self, conf, network, root_helper='sudo',
                 device_delegate=None, namespace=None, version=None):
        self.conf = conf
        self.network = network
        self.root_helper = root_helper
        self.device_delegate = device_delegate
        self.namespace = namespace
        self.version = version

    @abc.abstractmethod
    def enable(self):
        """Enables DHCP for this network."""

    @abc.abstractmethod
    def disable(self, retain_port=False):
        """Disable dhcp for this network."""

    def restart(self):
        """Restart the dhcp service for the network."""
        self.disable(retain_port=True)
        self.enable()

    @abc.abstractproperty
    def active(self):
        """Boolean representing the running state of the DHCP server."""

    @abc.abstractmethod
    def release_lease(self, mac_address, removed_ips):
        """Release a DHCP lease."""

    @abc.abstractmethod
    def reload_allocations(self):
        """Force the DHCP server to reload the assignment database."""

    @classmethod
    def existing_dhcp_networks(cls, conf, root_helper):
        """Return a list of existing networks ids that we have configs for."""

        raise NotImplementedError

    @classmethod
    def check_version(cls):
        """Execute version checks on DHCP server."""

        raise NotImplementedError


class DhcpLocalProcess(DhcpBase):
    PORTS = []

    def _enable_dhcp(self):
        """check if there is a subnet within the network with dhcp enabled."""
        for subnet in self.network.subnets:
            if subnet.enable_dhcp:
                return True
        return False

    def enable(self):
        """Enables DHCP for this network by spawning a local process."""
        interface_name = self.device_delegate.setup(self.network,
                                                    reuse_existing=True)
        if self.active:
            self.restart()
        elif self._enable_dhcp():
            self.interface_name = interface_name
            self.spawn_process()

    def disable(self, retain_port=False):
        """Disable DHCP for this network by killing the local process."""
        pid = self.pid

        if self.active:
            cmd = ['kill', '-9', pid]
            utils.execute(cmd, self.root_helper)
            if not retain_port:
                self.device_delegate.destroy(self.network, self.interface_name)

        elif pid:
            LOG.debug(_('DHCP for %(net_id)s pid %(pid)d is stale, ignoring '
                        'command'), {'net_id': self.network.id, 'pid': pid})
        else:
            LOG.debug(_('No DHCP started for %s'), self.network.id)

        self._remove_config_files()

    def _remove_config_files(self):
        confs_dir = os.path.abspath(os.path.normpath(self.conf.dhcp_confs))
        conf_dir = os.path.join(confs_dir, self.network.id)
        shutil.rmtree(conf_dir, ignore_errors=True)

    def get_conf_file_name(self, kind, ensure_conf_dir=False):
        """Returns the file name for a given kind of config file."""
        confs_dir = os.path.abspath(os.path.normpath(self.conf.dhcp_confs))
        conf_dir = os.path.join(confs_dir, self.network.id)
        if ensure_conf_dir:
            if not os.path.isdir(conf_dir):
                os.makedirs(conf_dir, 0o755)

        return os.path.join(conf_dir, kind)

    def _get_value_from_conf_file(self, kind, converter=None):
        """A helper function to read a value from one of the state files."""
        file_name = self.get_conf_file_name(kind)
        msg = _('Error while reading %s')

        try:
            with open(file_name, 'r') as f:
                try:
                    return converter and converter(f.read()) or f.read()
                except ValueError:
                    msg = _('Unable to convert value in %s')
        except IOError:
            msg = _('Unable to access %s')

        LOG.debug(msg % file_name)
        return None

    @property
    def pid(self):
        """Last known pid for the DHCP process spawned for this network."""
        return self._get_value_from_conf_file('pid', int)

    @property
    def active(self):
        pid = self.pid
        if pid is None:
            return False

        cmd = ['cat', '/proc/%s/cmdline' % pid]
        try:
            return self.network.id in utils.execute(cmd, self.root_helper)
        except RuntimeError:
            return False

    @property
    def interface_name(self):
        return self._get_value_from_conf_file('interface')

    @interface_name.setter
    def interface_name(self, value):
        interface_file_path = self.get_conf_file_name('interface',
                                                      ensure_conf_dir=True)
        utils.replace_file(interface_file_path, value)

    @abc.abstractmethod
    def spawn_process(self):
        pass


class Dnsmasq(DhcpLocalProcess):
    # The ports that need to be opened when security policies are active
    # on the Neutron port used for DHCP.  These are provided as a convenience
    # for users of this class.
    PORTS = {IPV4: [(UDP, DNS_PORT), (TCP, DNS_PORT), (UDP, DHCPV4_PORT)],
             IPV6: [(UDP, DNS_PORT), (TCP, DNS_PORT), (UDP, DHCPV6_PORT)],
             }

    _TAG_PREFIX = 'tag%d'

    NEUTRON_NETWORK_ID_KEY = 'NEUTRON_NETWORK_ID'
    NEUTRON_RELAY_SOCKET_PATH_KEY = 'NEUTRON_RELAY_SOCKET_PATH'
    MINIMUM_VERSION = 2.59

    @classmethod
    def check_version(cls):
        ver = 0
        try:
            cmd = ['dnsmasq', '--version']
            out = utils.execute(cmd)
            ver = re.findall("\d+.\d+", out)[0]
            is_valid_version = float(ver) >= cls.MINIMUM_VERSION
            if not is_valid_version:
                LOG.warning(_('FAILED VERSION REQUIREMENT FOR DNSMASQ. '
                              'DHCP AGENT MAY NOT RUN CORRECTLY! '
                              'Please ensure that its version is %s '
                              'or above!'), cls.MINIMUM_VERSION)
        except (OSError, RuntimeError, IndexError, ValueError):
            LOG.warning(_('Unable to determine dnsmasq version. '
                          'Please ensure that its version is %s '
                          'or above!'), cls.MINIMUM_VERSION)
        return float(ver)

    @classmethod
    def existing_dhcp_networks(cls, conf, root_helper):
        """Return a list of existing networks ids that we have configs for."""

        confs_dir = os.path.abspath(os.path.normpath(conf.dhcp_confs))

        class FakeNetwork:
            def __init__(self, net_id):
                self.id = net_id

        return [
            c for c in os.listdir(confs_dir)
            if (uuidutils.is_uuid_like(c) and
                cls(conf, FakeNetwork(c), root_helper).active)
        ]

    def spawn_process(self):
        """Spawns a Dnsmasq process for the network."""
        env = {
            self.NEUTRON_NETWORK_ID_KEY: self.network.id,
        }

        cmd = [
            'dnsmasq',
            '--no-hosts',
            '--no-resolv',
            '--strict-order',
            '--bind-interfaces',
            '--interface=%s' % self.interface_name,
            '--except-interface=lo',
            '--pid-file=%s' % self.get_conf_file_name(
                'pid', ensure_conf_dir=True),
            #TODO (mark): calculate value from cidr (defaults to 150)
            #'--dhcp-lease-max=%s' % ?,
            '--dhcp-hostsfile=%s' % self._output_hosts_file(),
            '--dhcp-optsfile=%s' % self._output_opts_file(),
            '--leasefile-ro',
        ]

        for i, subnet in enumerate(self.network.subnets):
            # if a subnet is specified to have dhcp disabled
            if not subnet.enable_dhcp:
                continue
            if subnet.ip_version == 4:
                mode = 'static'
            else:
                # TODO(mark): how do we indicate other options
                # ra-only, slaac, ra-nameservers, and ra-stateless.
                mode = 'static'
            if self.version >= self.MINIMUM_VERSION:
                set_tag = 'set:'
            else:
                set_tag = ''
            cmd.append('--dhcp-range=%s%s,%s,%s,%ss' %
                       (set_tag, self._TAG_PREFIX % i,
                        netaddr.IPNetwork(subnet.cidr).network,
                        mode,
                        self.conf.dhcp_lease_duration))

        cmd.append('--conf-file=%s' % self.conf.dnsmasq_config_file)
        if self.conf.dnsmasq_dns_server:
            cmd.append('--server=%s' % self.conf.dnsmasq_dns_server)

        if self.conf.dhcp_domain:
            cmd.append('--domain=%s' % self.conf.dhcp_domain)

        if self.namespace:
            ip_wrapper = ip_lib.IPWrapper(self.root_helper, self.namespace)
            ip_wrapper.netns.execute(cmd, addl_env=env)
        else:
            # For normal sudo prepend the env vars before command
            cmd = ['%s=%s' % pair for pair in env.items()] + cmd
            utils.execute(cmd, self.root_helper)

    def release_lease(self, mac_address, removed_ips):
        """Release a DHCP lease."""
        for ip in removed_ips or []:
            cmd = ['dhcp_release', self.interface_name, ip, mac_address]
            if self.namespace:
                ip_wrapper = ip_lib.IPWrapper(self.root_helper, self.namespace)
                ip_wrapper.netns.execute(cmd)
            else:
                utils.execute(cmd, self.root_helper)

    def reload_allocations(self):
        """Rebuild the dnsmasq config and signal the dnsmasq to reload."""

        # If all subnets turn off dhcp, kill the process.
        if not self._enable_dhcp():
            self.disable()
            LOG.debug(_('Killing dhcpmasq for network since all subnets have '
                        'turned off DHCP: %s'), self.network.id)
            return

        self._output_hosts_file()
        self._output_opts_file()
        if self.active:
            cmd = ['kill', '-HUP', self.pid]
            utils.execute(cmd, self.root_helper)
        else:
            LOG.debug(_('Pid %d is stale, relaunching dnsmasq'), self.pid)
        LOG.debug(_('Reloading allocations for network: %s'), self.network.id)

    def _output_hosts_file(self):
        """Writes a dnsmasq compatible hosts file."""
        r = re.compile('[:.]')
        buf = StringIO.StringIO()

        for port in self.network.ports:
            for alloc in port.fixed_ips:
                name = 'host-%s.%s' % (r.sub('-', alloc.ip_address),
                                       self.conf.dhcp_domain)
                buf.write('%s,%s,%s\n' %
                          (port.mac_address, name, alloc.ip_address))

        name = self.get_conf_file_name('host')
        utils.replace_file(name, buf.getvalue())
        return name

    def _output_opts_file(self):
        """Write a dnsmasq compatible options file."""

        if self.conf.enable_isolated_metadata:
            subnet_to_interface_ip = self._make_subnet_interface_ip_map()

        options = []
        for i, subnet in enumerate(self.network.subnets):
            if not subnet.enable_dhcp:
                continue
            if subnet.dns_nameservers:
                options.append(
                    self._format_option(i, 'dns-server',
                                        ','.join(subnet.dns_nameservers)))

            gateway = subnet.gateway_ip
            host_routes = []
            for hr in subnet.host_routes:
                if hr.destination == "0.0.0.0/0":
                    gateway = hr.nexthop
                else:
                    host_routes.append("%s,%s" % (hr.destination, hr.nexthop))

            # Add host routes for isolated network segments
            enable_metadata = (
                self.conf.enable_isolated_metadata
                and not subnet.gateway_ip
                and subnet.ip_version == 4)

            if enable_metadata:
                subnet_dhcp_ip = subnet_to_interface_ip[subnet.id]
                host_routes.append(
                    '%s/32,%s' % (METADATA_DEFAULT_IP, subnet_dhcp_ip)
                )

            if host_routes:
                options.append(
                    self._format_option(i, 'classless-static-route',
                                        ','.join(host_routes)))
                options.append(
                    self._format_option(i, WIN2k3_STATIC_DNS,
                                        ','.join(host_routes)))

            if subnet.ip_version == 4:
                if gateway:
                    options.append(self._format_option(i, 'router', gateway))
                else:
                    options.append(self._format_option(i, 'router'))

        name = self.get_conf_file_name('opts')
        utils.replace_file(name, '\n'.join(options))
        return name

    def _make_subnet_interface_ip_map(self):
        ip_dev = ip_lib.IPDevice(
            self.interface_name,
            self.root_helper,
            self.namespace
        )

        subnet_lookup = dict(
            (netaddr.IPNetwork(subnet.cidr), subnet.id)
            for subnet in self.network.subnets
        )

        retval = {}

        for addr in ip_dev.addr.list():
            ip_net = netaddr.IPNetwork(addr['cidr'])

            if ip_net in subnet_lookup:
                retval[subnet_lookup[ip_net]] = addr['cidr'].split('/')[0]

        return retval

    def _format_option(self, index, option, *args):
        """Format DHCP option by option name or code."""
        if self.version >= self.MINIMUM_VERSION:
            set_tag = 'tag:'
        else:
            set_tag = ''
        option = str(option)
        if not option.isdigit():
            option = 'option:%s' % option
        return ','.join((set_tag + self._TAG_PREFIX % index,
                         option) + args)

    @classmethod
    def lease_update(cls):
        network_id = os.environ.get(cls.NEUTRON_NETWORK_ID_KEY)
        dhcp_relay_socket = os.environ.get(cls.NEUTRON_RELAY_SOCKET_PATH_KEY)

        action = sys.argv[1]
        if action not in ('add', 'del', 'old'):
            sys.exit()

        mac_address = sys.argv[2]
        ip_address = sys.argv[3]

        if action == 'del':
            lease_remaining = 0
        else:
            lease_remaining = int(os.environ.get('DNSMASQ_TIME_REMAINING', 0))

        data = dict(network_id=network_id, mac_address=mac_address,
                    ip_address=ip_address, lease_remaining=lease_remaining)

        if os.path.exists(dhcp_relay_socket):
            sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
            sock.connect(dhcp_relay_socket)
            sock.send(jsonutils.dumps(data))
            sock.close()