#
# Copyright (C) 2006-2017  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 .locking import Lock, Empty
EMPTY = {}
NOBODY = []

def giant_lock(func):
    def wrapped(self, *args, **kw):
        self.lock_acquire()
        try:
            return func(self, *args, **kw)
        finally:
            self.lock_release()
    return wraps(func)(wrapped)

class Dispatcher:
    """Register a packet, connection pair as expecting a response packet."""

    def __init__(self):
        self.message_table = {}
        self.queue_dict = {}
        lock = Lock()
        self.lock_acquire = lock.acquire
        self.lock_release = lock.release

    @giant_lock
    def dispatch(self, conn, msg_id, packet, kw):
        """
        Retrieve register-time provided queue, and put conn and packet in it.
        """
        queue = self.message_table.get(id(conn), EMPTY).pop(msg_id, None)
        if queue is None:
            return False
        elif queue is NOBODY:
            return True
        self._decrefQueue(queue)
        queue.put((conn, packet, kw))
        return True

    def _decrefQueue(self, queue):
        queue_id = id(queue)
        queue_dict = self.queue_dict
        if queue_dict[queue_id] == 1:
            queue_dict.pop(queue_id)
        else:
            queue_dict[queue_id] -= 1

    def _increfQueue(self, queue):
        queue_id = id(queue)
        queue_dict = self.queue_dict
        try:
            queue_dict[queue_id] += 1
        except KeyError:
            queue_dict[queue_id] = 1

    @giant_lock
    def register(self, conn, msg_id, queue):
        """Register an expectation for a reply."""
        self.message_table.setdefault(id(conn), {})[msg_id] = queue
        self._increfQueue(queue)

    def unregister(self, conn):
        """ Unregister a connection and put fake packet in queues to unlock
        threads expecting responses from that connection """
        self.lock_acquire()
        try:
            message_table = self.message_table.pop(id(conn), EMPTY)
        finally:
            self.lock_release()
        notified_set = set()
        _decrefQueue = self._decrefQueue
        for queue in message_table.itervalues():
            if queue is NOBODY:
                continue
            queue_id = id(queue)
            if queue_id not in notified_set:
                queue.put((conn, None, None))
                notified_set.add(queue_id)
            _decrefQueue(queue)

    @giant_lock
    def forget_queue(self, queue, flush_queue=True):
        """
        Forget all pending messages for given queue.
        Actually makes them "expected by nobody", so we know we can ignore
        them, and not detect it as an error.
        flush_queue (boolean, default=True)
            All packets in queue get flushed.
        """
        # XXX: expensive lookup: we iterate over the whole dict
        found = 0
        for message_table in self.message_table.itervalues():
            for msg_id, t_queue in message_table.iteritems():
                if queue is t_queue:
                    found += 1
                    message_table[msg_id] = NOBODY
        refcount = self.queue_dict.pop(id(queue), 0)
        assert refcount == found, (refcount, found)
        if flush_queue:
            get = queue.get
            while True:
                try:
                    get(block=False)
                except Empty:
                    break

    def registered(self, conn):
        """Check if a connection is registered into message table."""
        return len(self.message_table.get(id(conn), EMPTY)) != 0

    @giant_lock
    def pending(self, queue):
        return not queue.empty() or self.queue_dict.get(id(queue), 0) > 0