#
# Copyright (C) 2006-2015  Nexedi SA
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 2
# of the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

from functools import wraps
from time import time

from . import attributeTracker, logging
from .connector import ConnectorException, ConnectorTryAgainException, \
        ConnectorInProgressException, ConnectorConnectionRefusedException, \
        ConnectorConnectionClosedException
from .locking import RLock
from .protocol import uuid_str, Errors, \
        PacketMalformedError, Packets, ParserState
from .util import ReadBuffer

CRITICAL_TIMEOUT = 30

connect_limit = 0

class ConnectionClosed(Exception):
    pass

def not_closed(func):
    def decorator(self, *args, **kw):
        if self.connector is None:
            raise ConnectorConnectionClosedException
        return func(self, *args, **kw)
    return wraps(func)(decorator)


def lockCheckWrapper(func):
    """
    This function is to be used as a wrapper around
    MT(Client|Server)Connection class methods.

    It uses a "_" method on RLock class, so it might stop working without
    notice (sadly, RLock does not offer any "acquired" method, but that one
    will do as it checks that current thread holds this lock).

    It requires moniroted class to have an RLock instance in self._lock
    property.
    """
    def wrapper(self, *args, **kw):
        if not self._lock._is_owned():
            import traceback
            logging.warning('%s called on %s instance without being locked.'
                ' Stack:\n%s', func.func_code.co_name,
                self.__class__.__name__, ''.join(traceback.format_stack()))
        # Call anyway
        return func(self, *args, **kw)
    return wraps(func)(wrapper)

class HandlerSwitcher(object):
    _next_timeout = None
    _next_timeout_msg_id = None
    _next_on_timeout = None

    def __init__(self, handler):
        # pending handlers and related requests
        self._pending = []
        self._is_handling = False
        self.setHandler(handler)

    def clear(self):
        self.__init__(self.getLastHandler())
        try:
            del (self._next_timeout,
                 self._next_timeout_msg_id,
                 self._next_on_timeout)
        except AttributeError:
            pass

    def isPending(self):
        return bool(self._pending[0][0])

    def cancelRequests(self, conn, message):
        if self.isPending():
            p = Errors.ProtocolError(message)
            while True:
                request_dict, handler = self._pending[0]
                while request_dict:
                    msg_id, request = request_dict.popitem()
                    p.setId(msg_id)
                    handler.packetReceived(conn, p, request[3])
                if len(self._pending) == 1:
                    break
                del self._pending[0]

    def getHandler(self):
        return self._pending[0][1]

    def getLastHandler(self):
        """ Return the last (may be unapplied) handler registered """
        return self._pending[-1][1]

    def emit(self, request, timeout, on_timeout, kw={}):
        # register the request in the current handler
        _pending = self._pending
        if self._is_handling:
            # If this is called while handling a packet, the response is to
            # be excpected for the current handler...
            (request_dict, _) = _pending[0]
        else:
            # ...otherwise, queue for the latest handler
            assert len(_pending) == 1 or _pending[0][0]
            (request_dict, _) = _pending[-1]
        msg_id = request.getId()
        answer_class = request.getAnswerClass()
        assert answer_class is not None, "Not a request"
        assert msg_id not in request_dict, "Packet id already expected"
        next_timeout = self._next_timeout
        if next_timeout is None or timeout < next_timeout:
            self._next_timeout = timeout
            self._next_timeout_msg_id = msg_id
            self._next_on_timeout = on_timeout
        request_dict[msg_id] = answer_class, timeout, on_timeout, kw

    def getNextTimeout(self):
        return self._next_timeout

    def timeout(self, connection):
        msg_id = self._next_timeout_msg_id
        if self._next_on_timeout is not None:
            self._next_on_timeout(connection, msg_id)
            if self._next_timeout_msg_id != msg_id:
                # on_timeout sent a packet with a smaller timeout
                # so keep the connection open
                return
        # Notify that a timeout occured
        return msg_id

    def handle(self, connection, packet):
        assert not self._is_handling
        self._is_handling = True
        try:
            self._handle(connection, packet)
        finally:
            self._is_handling = False

    def _handle(self, connection, packet):
        assert len(self._pending) == 1 or self._pending[0][0]
        logging.packet(connection, packet, False)
        if connection.isClosed() and packet.ignoreOnClosedConnection():
            logging.debug('Ignoring packet %r on closed connection %r',
                packet, connection)
            return
        msg_id = packet.getId()
        (request_dict, handler) = self._pending[0]
        # notifications are not expected
        if not packet.isResponse():
            handler.packetReceived(connection, packet)
            return
        # checkout the expected answer class
        try:
            klass, _, _, kw = request_dict.pop(msg_id)
        except KeyError:
            klass = None
            kw = {}
        if klass and isinstance(packet, klass) or packet.isError():
            handler.packetReceived(connection, packet, kw)
        else:
            logging.error('Unexpected answer %r in %r', packet, connection)
            if not connection.isClosed():
                notification = Packets.Notify('Unexpected answer: %r' % packet)
                connection.notify(notification)
                connection.abort()
            # handler.peerBroken(connection)
        # apply a pending handler if no more answers are pending
        while len(self._pending) > 1 and not self._pending[0][0]:
            del self._pending[0]
            logging.debug('Apply handler %r on %r', self._pending[0][1],
                    connection)
        if msg_id == self._next_timeout_msg_id:
            self._updateNextTimeout()

    def _updateNextTimeout(self):
        # Find next timeout and its msg_id
        next_timeout = None
        for pending in self._pending:
            for msg_id, (_, timeout, on_timeout, _) in pending[0].iteritems():
                if not next_timeout or timeout < next_timeout[0]:
                    next_timeout = timeout, msg_id, on_timeout
        self._next_timeout, self._next_timeout_msg_id, self._next_on_timeout = \
            next_timeout or (None, None, None)

    def setHandler(self, handler):
        can_apply = len(self._pending) == 1 and not self._pending[0][0]
        if can_apply:
            # nothing is pending, change immediately
            self._pending[0][1] = handler
        else:
            # put the next handler in queue
            self._pending.append([{}, handler])
        return can_apply


class BaseConnection(object):
    """A base connection

    About timeouts:

        Timeout are mainly per-connection instead of per-packet.
        The idea is that most of time, packets are received and processed
        sequentially, so if it takes a long for a peer to process a packet,
        following packets would just be enqueued.
        What really matters is that the peer makes progress in its work.
        As long as we receive an answer, we consider it's still alive and
        it may just have started to process the following request. So we reset
        timeouts.
        There is anyway nothing more we could do, because processing of a packet
        may be delayed in a very unpredictable way depending of previously
        received packets on peer side.
        Even ourself may be slow to receive a packet. We must not timeout for
        an answer that is already in our incoming buffer (read_buf or _queue).
        Timeouts in HandlerSwitcher are only there to prioritize some packets.
    """

    KEEP_ALIVE = 60

    def __init__(self, event_manager, handler, connector, addr=None):
        assert connector is not None, "Need a low-level connector"
        self.em = event_manager
        self.connector = connector
        self.addr = addr
        self._handlers = HandlerSwitcher(handler)
        event_manager.register(self)
        event_manager.addReader(self)

    # XXX: do not use getHandler
    getHandler      = property(lambda self: self._handlers.getHandler)
    getLastHandler  = property(lambda self: self._handlers.getLastHandler)
    isPending       = property(lambda self: self._handlers.isPending)

    def cancelRequests(self, *args, **kw):
        return self._handlers.cancelRequests(self, *args, **kw)

    def checkTimeout(self, t):
        pass

    def lock(self):
        return 1

    def unlock(self):
        return None

    def getConnector(self):
        return self.connector

    def getAddress(self):
        return self.addr

    def readable(self):
        raise NotImplementedError

    def writable(self):
        raise NotImplementedError

    def close(self):
        """Close the connection."""
        if self.connector is not None:
            em = self.em
            em.removeReader(self)
            em.removeWriter(self)
            em.unregister(self)
            self.connector.shutdown()
            self.connector.close()
            self.connector = None
            self.aborted = False

    def _getReprInfo(self):
        return [
            ('uuid', uuid_str(self.getUUID())),
            ('address', self.addr and '%s:%d' % self.addr or '?'),
            ('handler', self.getHandler()),
        ], ['closed'] if self.isClosed() else []

    def __repr__(self):
        address = self.addr and '%s:%d' % self.addr or '?'
        r, flags = self._getReprInfo()
        r = map('%s=%s'.__mod__, r)
        r += flags
        return '<%s(%s) at %x>' % (
            self.__class__.__name__,
            ', '.join(r),
            id(self),
        )

    __del__ = close

    def setHandler(self, handler):
        if self._handlers.setHandler(handler):
            logging.debug('Set handler %r on %r', handler, self)
        else:
            logging.debug('Delay handler %r on %r', handler, self)

    def getEventManager(self):
        return self.em

    def getUUID(self):
        return None

    def isClosed(self):
        return self.connector is None or self.isAborted()

    def isAborted(self):
        return False

    def isListening(self):
        return False

    def isServer(self):
        return False

    def isClient(self):
        return False

    def hasPendingMessages(self):
        return False

    def whoSetConnector(self):
        """
          Debugging method: call this method to know who set the current
          connector value.
        """
        return attributeTracker.whoSet(self, 'connector')

    def idle(self):
        pass


attributeTracker.track(BaseConnection)

class ListeningConnection(BaseConnection):
    """A listen connection."""

    def __init__(self, event_manager, handler, addr, connector, **kw):
        logging.debug('listening to %s:%d', *addr)
        BaseConnection.__init__(self, event_manager, handler,
                                addr=addr, connector=connector)
        self.connector.makeListeningConnection(addr)

    def readable(self):
        try:
            new_s, addr = self.connector.getNewConnection()
            logging.debug('accepted a connection from %s:%d', *addr)
            handler = self.getHandler()
            new_conn = ServerConnection(self.getEventManager(), handler,
                connector=new_s, addr=addr)
            handler.connectionAccepted(new_conn)
        except ConnectorTryAgainException:
            pass

    def getAddress(self):
        return self.connector.getAddress()

    def writable(self):
        return False

    def isListening(self):
        return True


class Connection(BaseConnection):
    """A connection."""

    # XXX: rename isPending, hasPendingMessages & pending methods

    connecting = False
    client = False
    server = False
    peer_id = None
    _base_timeout = None

    def __init__(self, event_manager, *args, **kw):
        BaseConnection.__init__(self, event_manager, *args, **kw)
        self.read_buf = ReadBuffer()
        self.write_buf = []
        self.cur_id = 0
        self.aborted = False
        self.uuid = None
        self._queue = []
        self._on_close = None
        self._parser_state = ParserState()

    def _getReprInfo(self):
        r, flags = super(Connection, self)._getReprInfo()
        if self._queue:
            r.append(('len(queue)', len(self._queue)))
        if self._on_close is not None:
            r.append(('on_close', getattr(self._on_close, '__name__', '?')))
        flags.extend(x for x in ('aborted', 'connecting', 'client', 'server')
                       if getattr(self, x))
        return r, flags

    def setOnClose(self, callback):
        self._on_close = callback

    def isClient(self):
        return self.client

    def isServer(self):
        return self.server

    def asClient(self):
        try:
            del self.idle
            assert self.client
        except AttributeError:
            self.client = True

    def asServer(self):
        self.server = True

    def _closeClient(self):
        if self.server:
            del self.idle
            self.client = False
            self.notify(Packets.CloseClient())
        else:
            self.close()

    def closeClient(self):
        if self.connector is not None and self.client:
            self.idle = self._closeClient

    def isAborted(self):
        return self.aborted

    def getUUID(self):
        return self.uuid

    def setUUID(self, uuid):
        self.uuid = uuid

    def setPeerId(self, peer_id):
        assert peer_id is not None
        self.peer_id = peer_id

    def getPeerId(self):
        return self.peer_id

    def _getNextId(self):
        next_id = self.cur_id
        self.cur_id = (next_id + 1) & 0xffffffff
        return next_id

    def updateTimeout(self, t=None):
        if not self._queue:
            if t:
                self._base_timeout = t
            self._timeout = self._handlers.getNextTimeout() or self.KEEP_ALIVE

    def checkTimeout(self, t):
        # first make sure we don't timeout on answers we already received
        if self._base_timeout and not self._queue:
            timeout = t - self._base_timeout
            if self._timeout <= timeout:
                handlers = self._handlers
                if handlers.isPending():
                    msg_id = handlers.timeout(self)
                    if msg_id is None:
                        self._base_timeout = t
                    else:
                        logging.info('timeout for #0x%08x with %r',
                                     msg_id, self)
                        self.close()
                else:
                    self.idle()

    def abort(self):
        """Abort dealing with this connection."""
        logging.debug('aborting a connector for %r', self)
        self.aborted = True
        assert self.write_buf
        if self._on_close is not None:
            self._on_close()
            self._on_close = None

    def writable(self):
        """Called when self is writable."""
        self._send()
        if not self.write_buf and self.connector is not None:
            if self.aborted:
                self.close()
            else:
                self.em.removeWriter(self)

    def readable(self):
        """Called when self is readable."""
        self._recv()
        self.analyse()
        if self.aborted:
            self.em.removeReader(self)

    def analyse(self):
        """Analyse received data."""
        try:
            while True:
                packet = Packets.parse(self.read_buf, self._parser_state)
                if packet is None:
                    break
                self._queue.append(packet)
        except PacketMalformedError, e:
            logging.error('malformed packet from %r: %s', self, e)
            self._closure()

    def hasPendingMessages(self):
        """
          Returns True if there are messages queued and awaiting processing.
        """
        return len(self._queue) != 0

    def process(self):
        """
          Process a pending packet.
        """
        # check out packet and process it with current handler
        packet = self._queue.pop(0)
        self._handlers.handle(self, packet)
        self.updateTimeout()

    def pending(self):
        return self.connector is not None and self.write_buf

    def close(self):
        if self.connector is None:
            assert self._on_close is None
            assert not self.read_buf
            assert not self.write_buf
            assert not self.isPending()
            return
        # process the network events with the last registered handler to
        # solve issues where a node is lost with pending handlers and
        # create unexpected side effects.
        handler = self._handlers.getLastHandler()
        super(Connection, self).close()
        if self._on_close is not None:
            self._on_close()
            self._on_close = None
        del self.write_buf[:]
        self.read_buf.clear()
        try:
            if self.connecting:
                handler.connectionFailed(self)
                self.connecting = False
            else:
                handler.connectionClosed(self)
        finally:
            self._handlers.clear()

    def _closure(self):
        assert self.connector is not None, self.whoSetConnector()
        while self._queue:
            self._handlers.handle(self, self._queue.pop(0))
        self.close()

    def _delayed_closure(self):
        # Wait at least 1 second between connection failures.
        global connect_limit
        t = time()
        if t < connect_limit:
            self.checkTimeout = lambda t: t < connect_limit or \
                self._delayed_closure()
            self.readable = self.writable = lambda: None
        else:
            connect_limit = t + 1
            self._closure()

    def _recv(self):
        """Receive data from a connector."""
        try:
            data = self.connector.receive()
        except ConnectorTryAgainException:
            pass
        except ConnectorConnectionRefusedException:
            assert self.connecting
            self._delayed_closure()
        except ConnectorConnectionClosedException:
            # connection resetted by peer, according to the man, this error
            # should not occurs but it seems it's false
            logging.debug('Connection reset by peer: %r', self.connector)
            self._closure()
        except:
            logging.debug('Unknown connection error: %r', self.connector)
            self._closure()
            # unhandled connector exception
            raise
        else:
            if not data:
                logging.debug('Connection %r closed in recv', self.connector)
                self._closure()
                return
            self._base_timeout = time() # last known remote activity
            self.read_buf.append(data)

    def _send(self):
        """Send data to a connector."""
        if not self.write_buf:
            return
        msg = ''.join(self.write_buf)
        try:
            n = self.connector.send(msg)
        except ConnectorTryAgainException:
            pass
        except ConnectorConnectionClosedException:
            # connection resetted by peer
            logging.debug('Connection reset by peer: %r', self.connector)
            self._closure()
        except:
            logging.debug('Unknown connection error: %r', self.connector)
            # unhandled connector exception
            self._closure()
            raise
        else:
            if not n:
                logging.debug('Connection %r closed in send', self.connector)
                self._closure()
                return
            if n == len(msg):
                del self.write_buf[:]
            else:
                self.write_buf = [msg[n:]]

    def _addPacket(self, packet):
        """Add a packet into the write buffer."""
        if self.connector is None:
            return

        was_empty = not self.write_buf

        self.write_buf.extend(packet.encode())

        if was_empty:
            # enable polling for writing.
            self.em.addWriter(self)
        logging.packet(self, packet, True)

    @not_closed
    def notify(self, packet):
        """ Then a packet with a new ID """
        msg_id = self._getNextId()
        packet.setId(msg_id)
        self._addPacket(packet)
        return msg_id

    @not_closed
    def ask(self, packet, timeout=CRITICAL_TIMEOUT, on_timeout=None, **kw):
        """
        Send a packet with a new ID and register the expectation of an answer
        """
        msg_id = self._getNextId()
        packet.setId(msg_id)
        self._addPacket(packet)
        handlers = self._handlers
        t = not handlers.isPending() and time() or None
        handlers.emit(packet, timeout, on_timeout, kw)
        self.updateTimeout(t)
        return msg_id

    @not_closed
    def answer(self, packet, msg_id=None):
        """ Answer to a packet by re-using its ID for the packet answer """
        if msg_id is None:
            msg_id = self.getPeerId()
        packet.setId(msg_id)
        assert packet.isResponse(), packet
        self._addPacket(packet)

    def idle(self):
        self.ask(Packets.Ping())


class ClientConnection(Connection):
    """A connection from this node to a remote node."""

    connecting = True
    client = True

    def __init__(self, event_manager, handler, node, connector):
        addr = node.getAddress()
        Connection.__init__(self, event_manager, handler, connector, addr)
        node.setConnection(self)
        handler.connectionStarted(self)
        try:
            try:
                self.connector.makeClientConnection(addr)
            except ConnectorInProgressException:
                event_manager.addWriter(self)
            else:
                self._connectionCompleted()
        except ConnectorConnectionRefusedException:
            self._delayed_closure()
        except ConnectorException:
            # unhandled connector exception
            self._closure()
            raise

    def writable(self):
        """Called when self is writable."""
        if self.connector.getError():
            self._delayed_closure()
        else:
            self._connectionCompleted()
            self.writable()

    def _connectionCompleted(self):
        self.writable = super(ClientConnection, self).writable
        self.connecting = False
        self.updateTimeout(time())
        self.getHandler().connectionCompleted(self)

class ServerConnection(Connection):
    """A connection from a remote node to this node."""

    # Both server and client must check the connection, in case:
    # - the remote crashed brutally (i.e. without closing TCP connections)
    # - or packets sent by the remote are dropped (network failure)
    # Use different timeout so that in normal condition, server never has to
    # ping the client. Otherwise, it would do it about half of the time.
    KEEP_ALIVE = Connection.KEEP_ALIVE + 5

    server = True

    def __init__(self, *args, **kw):
        Connection.__init__(self, *args, **kw)
        self.updateTimeout(time())


class MTClientConnection(ClientConnection):
    """A Multithread-safe version of ClientConnection."""

    def __metaclass__(name, base, d):
        for k in ('analyse', 'answer', 'checkTimeout',
                  'process', 'readable', 'writable'):
            d[k] = lockCheckWrapper(getattr(base[0], k).im_func)
        return type(name, base, d)

    def __init__(self, *args, **kwargs):
        # _lock is only here for lock debugging purposes. Do not use.
        self._lock = lock = RLock()
        self.lock = lock.acquire
        self.unlock = lock.release
        self.dispatcher = kwargs.pop('dispatcher')
        self.dispatcher.needPollThread()
        with lock:
            super(MTClientConnection, self).__init__(*args, **kwargs)

    def notify(self, *args, **kw):
        self.lock()
        try:
            return super(MTClientConnection, self).notify(*args, **kw)
        finally:
            self.unlock()

    def ask(self, packet, timeout=CRITICAL_TIMEOUT, on_timeout=None,
            queue=None, **kw):
        self.lock()
        try:
            if self.isClosed():
                raise ConnectionClosed
            # XXX: Here, we duplicate Connection.ask because we need to call
            # self.dispatcher.register after setId is called and before
            # _addPacket is called.
            msg_id = self._getNextId()
            packet.setId(msg_id)
            if queue is None:
                if type(packet) is not Packets.Ping:
                    raise TypeError, 'Only Ping packet can be asked ' \
                        'without a queue, got a %r.' % (packet, )
            else:
                self.dispatcher.register(self, msg_id, queue)
            self._addPacket(packet)
            handlers = self._handlers
            t = not handlers.isPending() and time() or None
            handlers.emit(packet, timeout, on_timeout, kw)
            self.updateTimeout(t)
            return msg_id
        finally:
            self.unlock()

    def close(self):
        self.lock()
        try:
            super(MTClientConnection, self).close()
        finally:
            self.unlock()
