#!@PYTHON@

# Copyright (C) 2011  Internet Systems Consortium.
#
# Permission to use, copy, modify, and distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SYSTEMS CONSORTIUM
# DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL
# INTERNET SYSTEMS CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT,
# INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING
# FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
# NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
# WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.


import sys; sys.path.append ('@@PYTHONPATH@@')
import isc
import bind10_config
from isc.dns import *
from isc.config.ccsession import *
from isc.cc import SessionError, SessionTimeout
import isc.util.process
import isc.util.io.socketsession
import select
import errno

from isc.log_messages.ddns_messages import *

from optparse import OptionParser, OptionValueError
import os
import os.path
import signal
import socket

isc.log.init("b10-ddns")
logger = isc.log.Logger("ddns")
TRACE_BASIC = logger.DBGLVL_TRACE_BASIC

DATA_PATH = bind10_config.DATA_PATH
SOCKET_FILE = DATA_PATH + '/ddns_socket'
if "B10_FROM_SOURCE" in os.environ:
    DATA_PATH = os.environ['B10_FROM_SOURCE'] + "/src/bin/ddns"
SPECFILE_LOCATION = DATA_PATH + "/ddns.spec"


isc.util.process.rename()

class DDNSConfigError(Exception):
    '''An exception indicating an error in updating ddns configuration.

    This exception is raised when the ddns process encounters an error in
    handling configuration updates.  Not all syntax error can be caught
    at the module-CC layer, so ddns needs to (explicitly or implicitly)
    validate the given configuration data itself.  When it finds an error
    it raises this exception (either directly or by converting an exception
    from other modules) as a unified error in configuration.
    '''
    pass

class DDNSSessionError(Exception):
    '''An exception raised for some unexpected events during a ddns session.
    '''
    pass

class DDNSSession:
    '''Class to handle one DDNS update'''

    def __init__(self):
        '''Initialize a DDNS Session'''
        pass

def clear_socket():
    '''
    Removes the socket file, if it exists.
    '''
    if os.path.exists(SOCKET_FILE):
        os.remove(SOCKET_FILE)

class DDNSServer:
    def __init__(self, cc_session=None):
        '''
        Initialize the DDNS Server.
        This sets up a ModuleCCSession for the BIND 10 system.
        Parameters:
        cc_session: If None (default), a new ModuleCCSession will be set up.
                    If specified, the given session will be used. This is
                    mainly used for testing.
        '''
        if cc_session is not None:
            self._cc = cc_session
        else:
            self._cc = isc.config.ModuleCCSession(SPECFILE_LOCATION,
                                                  self.config_handler,
                                                  self.command_handler)

        self._config_data = self._cc.get_full_config()
        self._cc.start()
        self._shutdown = False
        # List of the session receivers where we get the requests
        self._socksession_receivers = {}
        clear_socket()
        self._listen_socket = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
        self._listen_socket.bind(SOCKET_FILE)
        self._listen_socket.listen(16)

    def config_handler(self, new_config):
        '''Update config data.'''
        answer = create_answer(0)
        return answer

    def command_handler(self, cmd, args):
        '''
        Handle a CC session command, as sent from bindctl or other
        BIND 10 modules.
        '''
        if cmd == "shutdown":
            logger.info(DDNS_RECEIVED_SHUTDOWN_COMMAND)
            self.trigger_shutdown()
            answer = create_answer(0)
        else:
            answer = create_answer(1, "Unknown command: " + str(cmd))
        return answer

    def trigger_shutdown(self):
        '''Initiate a shutdown sequence.

        This method is expected to be called in various ways including
        in the middle of a signal handler, and is designed to be as simple
        as possible to minimize side effects.  Actual shutdown will take
        place in a normal control flow.

        '''
        logger.info(DDNS_SHUTDOWN)
        self._shutdown = True

    def shutdown_cleanup(self):
        '''
        Perform any cleanup that is necessary when shutting down the server.
        Do NOT call this to initialize shutdown, use trigger_shutdown().

        Currently, it does nothing, but cleanup routines are expected.
        '''
        pass

    def accept(self):
        """
        Accept another connection and create the session receiver.
        """
        socket = self._listen_socket.accept()
        fileno = socket.fileno()
        logger.debug(TRACE_BASIC, DDNS_NEW_CONN, fileno, socket.getpeername())
        receiver = isc.util.io.socketsession.SocketSessionReceiver(socket)
        self._socksession_receivers[fileno] = (socket, receiver)

    def handle_request(self, request):
        """
        This is the place where the actual DDNS processing is done. Other
        methods are either subroutines of this method or methods doing the
        uninteresting "accounting" stuff, like accepting socket,
        initialization, etc.

        It is called with the request being session as received from
        SocketSessionReceiver, i.e. tuple
        (socket, local_address, remote_address, data).
        """
        # TODO: Implement the magic
        pass

    def handle_session(self, fileno):
        """
        Handle incoming session on the socket with given fileno.
        """
        logger.debug(TRACE_BASIC, DDNS_SESSION, fileno)
        (socket, receiver) = self._socksession_receivers[fileno]
        try:
            self.handle_request(receiver.pop())
        except isc.util.io.socketsession.SocketSessionError as se:
            # No matter why this failed, the connection is in unknown, possibly
            # broken state. So, we close the socket and remove the receiver.
            del self._socksession_receivers[fileno]
            socket.close()
            logger.warn(DDNS_DROP_CONN, fileno, se)

    def run(self):
        '''
        Get and process all commands sent from cfgmgr or other modules.
        This loops waiting for events until self.shutdown() has been called.
        '''
        logger.info(DDNS_RUNNING)
        cc_fileno = self._cc.get_socket().fileno()
        listen_fileno = self._listen_socket.fileno()
        while not self._shutdown:
            # In this event loop we propage most of exceptions, which will
            # subsequently kill the b10-ddns process, but ideally it would be
            # better to catch any exceptions that b10-ddns can recover from.
            # We currently have no exception hierarchy to make such a
            # distinction easily, but once we do, we should catch and handle
            # non fatal exceptions here and continue the process.

            try:
                (reads, writes, exceptions) = \
                    select.select([cc_fileno, listen_fileno] +
                                  list(self._socksession_receivers.keys()), [],
                                  [])
            except select.error as se:
                # In case it is just interrupted, we continue like nothing
                # happened
                if se.args[0] == errno.EINTR:
                    (reads, writes, exceptions) = ([], [], [])
                else:
                    raise
            for fileno in reads:
                if fileno == cc_fileno:
                    self._cc.check_command(True)
                elif fileno == listen_fileno:
                    self.accept()
                else:
                    self.handle_session(fileno)
        self.shutdown_cleanup()
        logger.info(DDNS_STOPPED)

def create_signal_handler(ddns_server):
    '''
    This creates a signal_handler for use in set_signal_handler, which
    shuts down the given DDNSServer (or any object that has a shutdown()
    method)
    '''
    def signal_handler(signal, frame):
        '''
        Handler for process signals. Since only signals to shut down are sent
        here, the actual signal is not checked and the server is simply shut
        down.
        '''
        ddns_server.trigger_shutdown()
    return signal_handler

def set_signal_handler(signal_handler):
    '''
    Sets the signal handler(s).
    '''
    signal.signal(signal.SIGTERM, signal_handler)
    signal.signal(signal.SIGINT, signal_handler)

def set_cmd_options(parser):
    '''
    Helper function to set command-line options
    '''
    parser.add_option("-v", "--verbose", dest="verbose", action="store_true",
            help="display more about what is going on")

def main(ddns_server=None):
    '''
    The main function.
    Parameters:
    ddns_server: If None (default), a DDNSServer object is initialized.
                 If specified, the given DDNSServer will be used. This is
                 mainly used for testing.
    cc_session: If None (default), a new ModuleCCSession will be set up.
                If specified, the given session will be used. This is
                mainly used for testing.
    '''
    try:
        parser = OptionParser()
        set_cmd_options(parser)
        (options, args) = parser.parse_args()
        if options.verbose:
            print("[b10-ddns] Warning: -v verbose option is ignored at this point.")

        if ddns_server is None:
            ddns_server = DDNSServer()
        set_signal_handler(create_signal_handler(ddns_server))
        ddns_server.run()
    except KeyboardInterrupt:
        logger.info(DDNS_STOPPED_BY_KEYBOARD)
    except SessionError as e:
        logger.error(DDNS_CC_SESSION_ERROR, str(e))
    except ModuleCCSessionError as e:
        logger.error(DDNS_MODULECC_SESSION_ERROR, str(e))
    except DDNSConfigError as e:
        logger.error(DDNS_CONFIG_ERROR, str(e))
    except SessionTimeout as e:
        logger.error(DDNS_CC_SESSION_TIMEOUT_ERROR)
    except Exception as e:
        logger.error(DDNS_UNCAUGHT_EXCEPTION, type(e).__name__, str(e))
    clear_socket()

if '__main__' == __name__:
    main()