"""Implements twisted-based generic DGRAM transport"""
import sys
from twisted.internet.protocol import DatagramProtocol
from twisted.internet import reactor
from pysnmp.carrier.twisted.base import AbstractTwistedTransport
from pysnmp.carrier import error
from pysnmp import debug

class DgramTwistedTransport(DatagramProtocol, AbstractTwistedTransport):
    """Base Twisted datagram Transport, to be used with TwistedDispatcher"""

    # Twisted Datagram API
    
    def datagramReceived(self, datagram, address):
        if self._cbFun is None:
            raise error.CarrierError('Unable to call cbFun')
        else:
            # Callback fun is called through callLater() in attempt
            # to make Twisted timed calls work under high load.
            reactor.callLater(0, self._cbFun, self, address, datagram)

    def startProtocol(self):
        debug.logger & debug.flagIO and debug.logger('startProtocol: invoked')
        while self._writeQ:
            outgoingMessage, transportAddress = self._writeQ.pop(0)
            debug.logger & debug.flagIO and debug.logger('startProtocol: transportAddress %s outgoingMessage %s' % (transportAddress, repr(outgoingMessage)))
            try:
                self.transport.write(outgoingMessage, transportAddress)
            except Exception:
                raise error.CarrierError('Twisted exception: %s' % (sys.exc_info()[1],))

    def stopProtocol(self):
        debug.logger & debug.flagIO and debug.logger('stopProtocol: invoked')
        self.closeTransport()

    def sendMessage(self, outgoingMessage, transportAddress):
        debug.logger & debug.flagIO and debug.logger('startProtocol: %s transportAddress %s outgoingMessage %s' % ((self.transport is None and "queuing" or "sending"), transportAddress, repr(outgoingMessage)))        
        if self.transport is None:
            self._writeQ.append((outgoingMessage, transportAddress))
        else:
            try:
                self.transport.write(outgoingMessage, transportAddress)
            except Exception:
                raise error.CarrierError('Twisted exception: %s' % (sys.exc_info()[1],))
