# Copyright (C) 2012 Nippon Telegraph and Telephone Corporation.
#
# 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 struct

from . import packet_base
from . import packet_utils
from os_ken.lib import stringify


ICMP_ECHO_REPLY = 0
ICMP_DEST_UNREACH = 3
ICMP_SRC_QUENCH = 4
ICMP_REDIRECT = 5
ICMP_ECHO_REQUEST = 8
ICMP_TIME_EXCEEDED = 11

ICMP_ECHO_REPLY_CODE = 0
ICMP_HOST_UNREACH_CODE = 1
ICMP_PORT_UNREACH_CODE = 3
ICMP_TTL_EXPIRED_CODE = 0


class icmp(packet_base.PacketBase):
    """ICMP (RFC 792) header encoder/decoder class.

    An instance has the following attributes at least.
    Most of them are same to the on-wire counterparts but in host byte order.
    __init__ takes the corresponding args in this order.

    .. tabularcolumns:: |l|L|

    ============== ====================
    Attribute      Description
    ============== ====================
    type           Type
    code           Code
    csum           CheckSum \
                   (0 means automatically-calculate when encoding)
    data           Payload. \
                   Either a bytearray, or \
                   os_ken.lib.packet.icmp.echo or \
                   os_ken.lib.packet.icmp.dest_unreach or \
                   os_ken.lib.packet.icmp.TimeExceeded object \
                   NOTE for icmp.echo: \
                   This includes "unused" 16 bits and the following \
                   "Internet Header + 64 bits of Original Data Datagram" of \
                   the ICMP header. \
                   NOTE for icmp.dest_unreach and icmp.TimeExceeded: \
                   This includes "unused" 8 or 24 bits and the following \
                   "Internet Header + leading octets of original datagram" \
                   of the original packet.
    ============== ====================
    """

    _PACK_STR = '!BBH'
    _MIN_LEN = struct.calcsize(_PACK_STR)
    _ICMP_TYPES = {}

    @staticmethod
    def register_icmp_type(*args):
        def _register_icmp_type(cls):
            for type_ in args:
                icmp._ICMP_TYPES[type_] = cls
            return cls
        return _register_icmp_type

    def __init__(self, type_=ICMP_ECHO_REQUEST, code=0, csum=0, data=b''):
        super(icmp, self).__init__()
        self.type = type_
        self.code = code
        self.csum = csum
        self.data = data

    @classmethod
    def parser(cls, buf):
        (type_, code, csum) = struct.unpack_from(cls._PACK_STR, buf)
        msg = cls(type_, code, csum)
        offset = cls._MIN_LEN

        if len(buf) > offset:
            cls_ = cls._ICMP_TYPES.get(type_, None)
            if cls_:
                msg.data = cls_.parser(buf, offset)
            else:
                msg.data = buf[offset:]

        return msg, None, None

    def serialize(self, payload, prev):
        hdr = bytearray(struct.pack(icmp._PACK_STR, self.type,
                                    self.code, self.csum))

        if self.data:
            if self.type in icmp._ICMP_TYPES:
                assert isinstance(self.data, _ICMPv4Payload)
                hdr += self.data.serialize()
            else:
                hdr += self.data
        else:
            self.data = echo()
            hdr += self.data.serialize()

        if self.csum == 0:
            self.csum = packet_utils.checksum(hdr)
            struct.pack_into('!H', hdr, 2, self.csum)

        return hdr

    def __len__(self):
        return self._MIN_LEN + len(self.data)


class _ICMPv4Payload(stringify.StringifyMixin, metaclass=abc.ABCMeta):
    """
    Base class for the payload of ICMPv4 packet.
    """


@icmp.register_icmp_type(ICMP_ECHO_REPLY, ICMP_ECHO_REQUEST)
class echo(_ICMPv4Payload):
    """ICMP sub encoder/decoder class for Echo and Echo Reply messages.

    This is used with os_ken.lib.packet.icmp.icmp for
    ICMP Echo and Echo Reply messages.

    An instance has the following attributes at least.
    Most of them are same to the on-wire counterparts but in host byte order.
    __init__ takes the corresponding args in this order.

    .. tabularcolumns:: |l|L|

    ============== ====================
    Attribute      Description
    ============== ====================
    id             Identifier
    seq            Sequence Number
    data           Internet Header + 64 bits of Original Data Datagram
    ============== ====================
    """

    _PACK_STR = '!HH'
    _MIN_LEN = struct.calcsize(_PACK_STR)

    def __init__(self, id_=0, seq=0, data=None):
        super(echo, self).__init__()
        self.id = id_
        self.seq = seq
        self.data = data

    @classmethod
    def parser(cls, buf, offset):
        (id_, seq) = struct.unpack_from(cls._PACK_STR, buf, offset)
        msg = cls(id_, seq)
        offset += cls._MIN_LEN

        if len(buf) > offset:
            msg.data = buf[offset:]

        return msg

    def serialize(self):
        hdr = bytearray(struct.pack(echo._PACK_STR, self.id,
                                    self.seq))

        if self.data is not None:
            hdr += self.data

        return hdr

    def __len__(self):
        length = self._MIN_LEN
        if self.data is not None:
            length += len(self.data)
        return length


@icmp.register_icmp_type(ICMP_DEST_UNREACH)
class dest_unreach(_ICMPv4Payload):
    """ICMP sub encoder/decoder class for Destination Unreachable Message.

    This is used with os_ken.lib.packet.icmp.icmp for
    ICMP Destination Unreachable Message.

    An instance has the following attributes at least.
    Most of them are same to the on-wire counterparts but in host byte order.
    __init__ takes the corresponding args in this order.

    [RFC1191] reserves bits for the "Next-Hop MTU" field.
    [RFC4884] introduced 8-bit data length attribute.

    .. tabularcolumns:: |l|p{35em}|

    ============== =====================================================
    Attribute      Description
    ============== =====================================================
    data_len       data length
    mtu            Next-Hop MTU

                   NOTE: This field is required when icmp code is 4

                   code 4 = fragmentation needed and DF set
    data           Internet Header + leading octets of original datagram
    ============== =====================================================
    """

    _PACK_STR = '!xBH'
    _MIN_LEN = struct.calcsize(_PACK_STR)

    def __init__(self, data_len=0, mtu=0, data=None):
        super(dest_unreach, self).__init__()

        if ((data_len >= 0) and (data_len <= 255)):
            self.data_len = data_len
        else:
            raise ValueError('Specified data length (%d) is invalid.' % data_len)

        self.mtu = mtu
        self.data = data

    @classmethod
    def parser(cls, buf, offset):
        (data_len, mtu) = struct.unpack_from(cls._PACK_STR,
                                             buf, offset)
        msg = cls(data_len, mtu)
        offset += cls._MIN_LEN

        if len(buf) > offset:
            msg.data = buf[offset:]

        return msg

    def serialize(self):
        hdr = bytearray(struct.pack(dest_unreach._PACK_STR,
                                    self.data_len, self.mtu))

        if self.data is not None:
            hdr += self.data

        return hdr

    def __len__(self):
        length = self._MIN_LEN
        if self.data is not None:
            length += len(self.data)
        return length


@icmp.register_icmp_type(ICMP_TIME_EXCEEDED)
class TimeExceeded(_ICMPv4Payload):
    """ICMP sub encoder/decoder class for Time Exceeded Message.

    This is used with os_ken.lib.packet.icmp.icmp for
    ICMP Time Exceeded Message.

    An instance has the following attributes at least.
    Most of them are same to the on-wire counterparts but in host byte order.
    __init__ takes the corresponding args in this order.

    [RFC4884] introduced 8-bit data length attribute.

    .. tabularcolumns:: |l|L|

    ============== ====================
    Attribute      Description
    ============== ====================
    data_len       data length
    data           Internet Header + leading octets of original datagram
    ============== ====================
    """

    _PACK_STR = '!xBxx'
    _MIN_LEN = struct.calcsize(_PACK_STR)

    def __init__(self, data_len=0, data=None):
        if (data_len >= 0) and (data_len <= 255):
            self.data_len = data_len
        else:
            raise ValueError('Specified data length (%d) is invalid.' % data_len)

        self.data = data

    @classmethod
    def parser(cls, buf, offset):
        (data_len, ) = struct.unpack_from(cls._PACK_STR, buf, offset)
        msg = cls(data_len)
        offset += cls._MIN_LEN

        if len(buf) > offset:
            msg.data = buf[offset:]

        return msg

    def serialize(self):
        hdr = bytearray(struct.pack(TimeExceeded._PACK_STR, self.data_len))

        if self.data is not None:
            hdr += self.data

        return hdr

    def __len__(self):
        length = self._MIN_LEN
        if self.data is not None:
            length += len(self.data)
        return length


icmp.set_classes(icmp._ICMP_TYPES)