#!/usr/bin/python3

import sys
import os

import twisted
import twisted.internet
import twisted.internet.endpoints
from twisted.internet import reactor
from twisted.web.server import NOT_DONE_YET
from twisted.logger import LogLevel

import ipaddress
from ipaddress import AddressValueError

#import twisted.web.server import Site
#from twisted.web.resource import Resource

from optparse import OptionParser
from configparser import ConfigParser
from configparser import NoOptionError

import collections

import syslog

clients = { }

def ipaddr(input):
  try:
    r = ipaddress.IPv4Address(input)
  except AddressValueError:
    r = ipaddress.IPv6Address(input)
  return r

def ipnetwork(input):
  try:
    r = ipaddress.IPv4Network(input)
  except NetworkValueError:
    r = ipaddress.IPv6Network(input)
  return r

defcfg = '''
[DEFAULT]
max_batch_down = 65536
max_queue_time = 10
max_request_time = 54

[virtual]
mtu = 1500
# network
# [host]
# [relay]

[server]
ipif = userv root ipif %(host)s,%(relay)s,%(mtu)s,slip %(network)s
addrs = 127.0.0.1 ::1
port = 80

[limits]
max_batch_down = 262144
max_queue_time = 121
max_request_time = 121
'''

#---------- "router" ----------

def route(packet, daddr):
  try: client = clients[daddr]
  except KeyError: dclient = None
  if dclient is not None:
    dclient.queue_outbound(packet)
  elif daddr == host or daddr not in network:
    queue_inbound(packet)
  elif daddr == relay:
    log_discard(packet, saddr, daddr, 'relay')
  else:
    log_discard(packet, saddr, daddr, 'no client')

def log_discard(packet, saddr, daddr, why):
  syslog.syslog(syslog.LOG_DEBUG,
                'discarded packet %s -> %s (%s)' % (saddr, daddr, why))

#---------- ipif (slip subprocess) ----------

class IpifProcessProtocol(twisted.internet.protocol.ProcessProtocol):
  def __init__(self):
    self._buffer = b''
  def connectionMade(self): pass
  def outReceived(self, data):
    self._buffer += data
    packets = slip_decode(self._buffer)
    self._buffer = packets.pop()
    for packet in packets:
      (saddr, daddr) = packet_addrs(packet)
      route(packet, daddr)
  def processEnded(self, status):
    status.raiseException()

def start_ipif():
  global ipif
  ipif = IpifProcessProtocol()
  reactor.spawnProcess(ipif,
                       '/bin/sh',['sh','-c', ipif_command],
                       childFDs={0:'w', 1:'r', 2:2})

def queue_inbound(packet):
  ipif.transport.write(slip_delimiter)
  ipif.transport.write(slip_encode(packet))
  ipif.transport.write(slip_delimiter)

#---------- client ----------

class Client():
  def __init__(self, ip, cs):
    # instance data members
    self._ip = ip
    self._cs = cs
    self.pw = cfg.get(cs, 'password')
    self._rq = collections.deque() # requests
    self._pq = collections.deque() # packets
    # plus from config:
    #  .max_batch_down
    #  .max_queue_time
    #  .max_request_time
    for k in ('max_batch_down','max_queue_time','max_request_time'):
      req = cfg.getint(cs, k)
      limit = cfg.getint('limits',k)
      self.__dict__[k] = min(req, limit)

    def process_arriving_data(self, d):
      for packet in slip_decode(d):
        (saddr, daddr) = packet_addrs(packet)
        if saddr != self._ip:
          raise ValueError('wrong source address %s' % saddr)
        route(packet, daddr)

    def _req_cancel(self, request):
      request.finish()

    def _req_error(self, err, request):
      self._req_cancel(request)

    def queue_outbound(self, packet):
      self._pq.append((time.monotonic(), packet))

    def http_request(self, request):
      request.setHeader('Content-Type','application/octet-stream')
      reactor.callLater(self.max_request_time, self._req_cancel, request)
      request.notifyFinish().addErrback(self._req_error, request)
      self._rq.append(request)
      self._check_outbound()

    def _check_outbound(self):
      while True:
        try: request = self._rq[0]
        except IndexError: request = None
        if request and request.finished:
          self._rq.popleft()
          continue

        # now request is an unfinished request, or None
        try: (queuetime, packet) = self._pq[0]
        except IndexError:
          # no packets, oh well
          break

        age = time.monotonic() - queuetime
        if age > self.max_queue_time:
          self._pq.popleft()
          continue

        if request is None:
          # no request
          break

        # request, and also some non-expired packets
        while True:
          try: (dummy, packet) = self._pq[0]
          except IndexError: break

          encoded = slip_encode(packet)
          
          if request.sentLength > 0:
            if (request.sentLength + len(slip_delimiter)
                + len(encoded) > self.max_batch_down):
              break
            request.write(slip_delimiter)

          request.write(encoded)
          self._pq.popLeft()

        assert(request.sentLength)
        self._rq.popLeft()
        request.finish()
        # round again, looking for more to do

class IphttpResource(twisted.web.resource.Resource):
  def render_POST(self, request):
    # find client, update config, etc.
    ci = ipaddr(request.args['i'])
    c = clients[ci]
    pw = request.args['pw']
    if pw != c.pw: raise ValueError('bad password')

    # update config
    for r, w in (('mbd', 'max_batch_down'),
                 ('mqt', 'max_queue_time'),
                 ('mrt', 'max_request_time')):
      try: v = request.args[r]
      except KeyError: continue
      v = int(v)
      c.__dict__[w] = v

    try: d = request.args['d']
    except KeyError: d = ''

    c.process_arriving_data(d)
    c.new_request(request)

def start_http():
  resource = IphttpResource()
  sitefactory = twisted.web.server.Site(resource)
  for addrspec in cfg.get('server','addrs').split():
    try:
      addr = ipaddress.IPv4Address(addrspec)
      endpointfactory = twisted.internet.endpoints.TCP4ServerEndpoint
    except AddressValueError:
      addr = ipaddress.IPv6Address(addrspec)
      endpointfactory = twisted.internet.endpoints.TCP6ServerEndpoint
    ep = endpointfactory(reactor, cfg.getint('server','port'), addr)
    ep.listen(sitefactory)

#---------- config and setup ----------
        
def process_cfg():
  global network
  global host
  global relay
  global ipif_command

  network = ipnetwork(cfg.get('virtual','network'))
  if network.num_addresses < 3 + 2:
    raise ValueError('network needs at least 2^3 addresses')

  try:
    host = cfg.get('virtual','host')
  except NoOptionError:
    host = next(network.hosts())

  try:
    relay = cfg.get('virtual','relay')
  except NoOptionError:
    for search in network.hosts():
      if search == host: continue
      relay = search
      break

  for cs in cfg.sections():
    if not (':' in cs or '.' in cs): continue
    ci = ipaddr(cs)
    if ci not in network:
      raise ValueError('client %s not in network' % ci)
    if ci in clients:
      raise ValueError('multiple client cfg sections for %s' % ci)
    clients[ci] = Client(ci, cs)

  global mtu
  mtu = cfg.get('virtual','mtu')

  iic_vars = { }
  for k in ('host','relay','mtu','network'):
    iic_vars[k] = globals()[k]

  ipif_command = cfg.get('server','ipif', vars=iic_vars)

def crash_on_critical(event):
  if event.get('log_level') >= LogLevel.critical:
    print('crashing: ', twisted.logger.formatEvent(event), file=sys.stderr)
    #print('crashing!', file=sys.stderr)
    #os._exit(1)
    try: reactor.stop()
    except twisted.internet.error.ReactorNotRunning: pass

def startup():
  global cfg

  op = OptionParser()
  op.add_option('-c', '--config', dest='configfile',
                default='/etc/hippottd/server.conf')
  global opts
  (opts, args) = op.parse_args()
  if len(args): op.error('no non-option arguments please')

  twisted.logger.globalLogPublisher.addObserver(crash_on_critical)

  cfg = ConfigParser()
  cfg.read_string(defcfg)
  cfg.read(opts.configfile)
  process_cfg()

  start_ipif()
  start_http()

startup()
reactor.run()