#
# Copyright 2016 the original author or authors.
#
# 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.
#

"""
A module that can send and receive raw ethernet frames on a set of interfaces
and it can manage a set of vlan interfaces on top of existing
interfaces. Due to reliance on raw sockets, this module requires
root access. Also, raw sockets are hard to deal with in Twisted (not
directly supported) we need to run the receiver select loop on a dedicated
thread.
"""
import os
import socket
from pcapy import BPFProgram
from threading import Thread, Condition

import fcntl

import select
import structlog

from twisted.internet import reactor

from common.frameio.third_party.oftest import afpacket, netutils

log = structlog.get_logger()


def hexify(buffer):
    """
    Return a hexadecimal string encoding of input buffer
    """
    return ' '.join('%02x' % ord(c) for c in buffer)


class _SelectWakerDescriptor(object):
    """
    A descriptor that can be mixed into a select loop to wake it up.
    """
    def __init__(self):
        self.pipe_read, self.pipe_write = os.pipe()
        fcntl.fcntl(self.pipe_write, fcntl.F_SETFL, os.O_NONBLOCK)

    def __del__(self):
        os.close(self.pipe_read)
        os.close(self.pipe_write)

    def fileno(self):
        return self.pipe_read

    def wait(self):
        os.read(self.pipe_read, 1)

    def notify(self):
        """Trigger a select loop"""
        os.write(self.pipe_write, '\x00')


class BpfProgramFilter(object):
    """
    Convenience packet filter based on the well-tried Berkeley Packet Filter,
    used by many well known open source tools such as pcap and tcpdump.
    """
    def __init__(self, program_string):
        """
        Create a filter using the BPF command syntax. To learn more,
        consult 'man pcap-filter'.
        :param program_string: The textual definition of the filter. Examples:
        'vlan 1000'
        'vlan 1000 and ip src host 10.10.10.10'
        """
        self.bpf = BPFProgram(program_string)

    def __call__(self, frame):
        """
        Return 1 if frame passes filter.
        :param frame: Raw frame provided as Python string
        :return: 1 if frame satisfies filter, 0 otherwise.
        """
        return self.bpf.filter(frame)


class FrameIOPort(object):
    """
    Represents a network interface which we can send/receive raw
    Ethernet frames.
    """

    RCV_SIZE_DEFAULT = 4096
    ETH_P_ALL = 0x03
    RCV_TIMEOUT = 10000

    def __init__(self, iface_name, callback, filter=None):
        self.iface_name = iface_name
        self.callback = callback
        self.filter = filter
        self.socket = socket.socket(socket.AF_PACKET, socket.SOCK_RAW, 0)
        afpacket.enable_auxdata(self.socket)
        self.socket.bind((self.iface_name, self.ETH_P_ALL))
        netutils.set_promisc(self.socket, self.iface_name)
        self.socket.settimeout(self.RCV_TIMEOUT)
        log.debug('socket-opened', fn=self.fileno(), iface=iface_name)

        self.received = 0
        self.discarded = 0

    def __del__(self):
        if self.socket:
            fn = self.fileno()
            self.socket.close()
            self.socket = None
            log.debug('socket-closed', fn=fn, iface=self.iface_name)

    def fileno(self):
        return self.socket.fileno()

    def _dispatch(self, frame):
        log.debug('calling-publisher', frame=hexify(frame))
        self.callback(self, frame)

    def recv(self):
        """Called on the select thread when a packet arrives"""
        try:
            frame = afpacket.recv(self.socket, self.RCV_SIZE_DEFAULT)
        except RuntimeError, e:
            # we observed this happens sometimes right after the socket was
            # attached to a newly created veth interface. So we log it, but
            # allow to continue
            log.warn('afpacket-recv-error', code=-1)
            return

        log.debug('frame-received', iface=self.iface_name, len=len(frame),
                  hex=hexify(frame))
        self.received +=1
        if self.filter is None or self.filter(frame):
            log.debug('frame-dispatched')
            reactor.callFromThread(self._dispatch, frame)
        else:
            self.discarded += 1
            log.debug('frame-discarded')

    def send(self, frame):
        log.debug('sending', len=len(frame), iface=self.iface_name)
        sent_bytes = self.socket.send(frame)
        if sent_bytes != len(frame):
            log.error('send-error', iface=self.iface_name,
                      wanted_to_send=len(frame), actually_sent=sent_bytes)
        return sent_bytes

    def up(self):
        os.system('ip link set {} up'.format(self.iface_name))
        return self

    def down(self):
        os.system('ip link set {] down'.format(self.iface_name))
        return self

    def statistics(self):
        return self.received, self.discarded


class FrameIOManager(Thread):
    """
    Packet/Frame IO manager that can be used to send/receive raw frames
    on a set of network interfaces.
    """
    def __init__(self):
        super(FrameIOManager, self).__init__()

        self.ports = {}  # iface_name -> ActiveFrameReceiver
        self.queue = {}  # iface_name -> TODO

        self.cvar = Condition()
        self.waker = _SelectWakerDescriptor()
        self.stopped = False
        self.ports_changed = False

    #~~~~~~~~~~~ exposed methods callable from main thread ~~~~~~~~~~~~~~~~~~~~~

    def start(self):
        """
        Start the IO manager and its select loop thread
        """
        log.debug('starting')
        super(FrameIOManager, self).start()
        log.info('started')
        return self

    def stop(self):
        """
        Stop the IO manager and its thread with the select loop
        """
        log.debug('stopping')
        self.stopped = True
        self.waker.notify()
        self.join()
        del self.ports
        log.info('stopped')

    def list_interfaces(self):
        """
        Return list of interfaces listened on
        :return: List of FrameIOPort objects
        """
        return self.ports

    def add_interface(self, iface_name, callback, filter=None):
        """
        Add a new interface and start receiving on it.
        :param iface_name: Name of the interface. Must be an existing Unix
        interface (eth0, en0, etc.)
        :param callback: Called on each received frame;
        signature: def callback(port, frame) where port is the FrameIOPort
        instance at which the frame was received, frame is the actual frame
        received (as binay string)
        :param filter: An optional filter (predicate), with signature:
        def filter(frame). If provided, only frames for which filter evaluates
        to True will be forwarded to callback.
        :return: FrmaeIOPort instance.
        """
        """Add a new interface"""
        assert iface_name not in self.ports
        port = FrameIOPort(iface_name, callback, filter)
        self.ports[iface_name] = port
        # need to exit select loop to reconstruct select fd lists
        self.ports_changed = True
        self.waker.notify()
        return port

    def del_interface(self, iface_name):
        """
        Stop and remove named interface
        :param iface_name: Name of previoysly registered interface
        :return: None
        """
        assert iface_name in self.ports
        port = self.ports[iface_name]
        port.stop()
        del self.ports[iface_name]
        # need to exit select loop to reconstruct select fd lists
        self.ports_changed = True
        self.waker.notify()

    def send(self, iface_name, frame):
        """
        Send frame on given interface
        :param iface_name: Name of previously registered interface
        :param frame: frame as string
        :return: number of bytes sent
        """
        return self.ports[iface_name].send(frame)

    #~~~~~~~~~~~~~~ Thread methods (running on non-main thread ~~~~~~~~~~~~~~~~

    def run(self):
        """
        Called on the alien thread, this is the core multi-port receive loop
        """

        log.debug('select-loop-started')

        # outer loop constructs sockets list for select
        while not self.stopped:
            sockets = [self.waker] + self.ports.values()
            self.ports_changed = False
            empty = []
            # inner select loop

            while not self.stopped:
                try:
                    _in, _out, _err = select.select(sockets, empty, empty, 1)
                except Exception, e:
                    log.exception('frame-io-select-error', e=e)
                    break
                with self.cvar:
                    for port in _in:
                        if port is self.waker:
                            self.waker.wait()
                            continue
                        else:
                            port.recv()
                    self.cvar.notify_all()
                if self.ports_changed:
                    break  # break inner loop so we reconstruct sockets list

        log.debug('select-loop-exited')