#!/usr/bin/env python
# Copyright (c) 2016 Cisco and/or its affiliates.
# 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.

"""Router advertisement check script."""

import sys
import ipaddress

from resources.libraries.python.PacketVerifier import RxQueue
from resources.libraries.python.TrafficScriptArg import TrafficScriptArg


def mac_to_ipv6_linklocal(mac):
    """Transfer MAC address into specific link-local IPv6 address.

    :param mac: MAC address to be transferred.
    :type mac: str
    :return: IPv6 link-local address.
    :rtype: str
    """
    # Remove the most common delimiters: dots, dashes, etc.
    mac_value = int(mac.translate(None, ' .:-'), 16)

    # Split out the bytes that slot into the IPv6 address
    # XOR the most significant byte with 0x02, inverting the
    # Universal / Local bit
    high2 = mac_value >> 32 & 0xffff ^ 0x0200
    high1 = mac_value >> 24 & 0xff
    low1 = mac_value >> 16 & 0xff
    low2 = mac_value & 0xffff

    return 'fe80::{:04x}:{:02x}ff:fe{:02x}:{:04x}'.format(
        high2, high1, low1, low2)


def main():
    """Check packets on specific port and look for the Router Advertisement
     part.
    """

    args = TrafficScriptArg(['src_mac', 'interval'])

    rx_if = args.get_arg('rx_if')
    src_mac = args.get_arg('src_mac')
    interval = int(args.get_arg('interval'))
    rxq = RxQueue(rx_if)

    ether = rxq.recv(max(5, interval))

    # Check whether received packet contains layer RA and check other values
    if ether is None:
        raise RuntimeError('ICMP echo Rx timeout')

    if not ether.haslayer('ICMPv6ND_RA'):
        raise RuntimeError('Not an RA packet received {0}'
                           .format(ether.__repr__()))

    src_address = ipaddress.IPv6Address(unicode(ether['IPv6'].src))
    dst_address = ipaddress.IPv6Address(unicode(ether['IPv6'].dst))
    link_local = ipaddress.IPv6Address(unicode(mac_to_ipv6_linklocal(src_mac)))
    all_nodes_multicast = ipaddress.IPv6Address(u'ff02::1')

    if src_address != link_local:
        raise RuntimeError(
            'Source address ({0}) not matching link local address({1})'.format(
                src_address, link_local))
    if dst_address != all_nodes_multicast:
        raise RuntimeError('Packet destination address ({0}) is not the all '
                           'nodes multicast address ({1}).'.format(
                            dst_address, all_nodes_multicast))
    if ether['IPv6'].hlim != 255:
        raise RuntimeError('Hop limit not correct: {0}!=255'.format(
            ether['IPv6'].hlim))

    ra_code = ether['ICMPv6 Neighbor Discovery - Router Advertisement'].code
    if ra_code != 0:
        raise RuntimeError('ICMP code: {0} not correct. '.format(ra_code))

    sys.exit(0)

if __name__ == "__main__":
    main()