# @author Bob Ippolito
#
# Copyright (c) 2005-2006, Bob Ippolito
# Copyright (c) 2007, Linden Research, Inc.
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

import collections

from eventlib import api
from eventlib.support import greenlets as greenlet

__all__ = ['channel']

class channel(object):
    """A channel is a control flow primitive for co-routines. It is a
    "thread-like" queue for controlling flow between two (or more) co-routines.
    The state model is:

    * If one co-routine calls send(), it is unscheduled until another
      co-routine calls receive().
    * If one co-rounte calls receive(), it is unscheduled until another
      co-routine calls send().
    * Once a paired send()/receive() have been called, both co-routeines
      are rescheduled.

    This is similar to: http://stackless.com/wiki/Channels
    """
    balance = 0

    def _tasklet_loop(self):
        deque = self.deque = collections.deque()
        hub = api.get_hub()
        current = greenlet.getcurrent()
        def switch(g, value=None, exc=None):
            if exc is None:
                return g.switch(value)
            else:
                return g.throw(exc)
        direction, caller, args = switch(current.parent or current)
        try:
            while True:
                if direction == -1:
                    # waiting to receive
                    if self.balance > 0:
                        sender, args = deque.popleft()
                        hub.schedule_call(0, switch, sender)
                        hub.schedule_call(0, switch, caller, *args)
                    else:
                        deque.append(caller)
                else:
                    # waiting to send
                    if self.balance < 0:
                        receiver = deque.popleft()
                        hub.schedule_call(0, switch, receiver, *args)
                        hub.schedule_call(0, switch, caller)
                    else:
                        deque.append((caller, args))
                self.balance += direction
                direction, caller, args = hub.switch()
        finally:
            deque.clear()
            del self.deque
            self.balance = 0

    def _send_tasklet(self, *args):
        try:
            t = self._tasklet
        except AttributeError:
            t = self._tasklet = greenlet.greenlet(self._tasklet_loop)
            t.switch()
        if args:
            return t.switch((1, greenlet.getcurrent(), args))
        else:
            return t.switch((-1, greenlet.getcurrent(), args))

    def receive(self):
        return self._send_tasklet()

    def send(self, value):
        return self._send_tasklet(value)

    def send_exception(self, exc):
        return self._send_tasklet(None, exc)

import warnings
warnings.warn("channel is deprecated; use coros.queue(0) which behaves the same", DeprecationWarning, stacklevel=2)