import asyncio

from itertools import count

class BaseSignal(list):

@asyncio.coroutine

def _send(self, *args, **kwargs):

for receiver in self:

res = receiver(*args, **kwargs)

if asyncio.iscoroutine(res) or isinstance(res, asyncio.Future):

yield from res

def copy(self):

raise NotImplementedError("copy() is forbidden")

def sort(self):

raise NotImplementedError("sort() is forbidden")

class Signal(BaseSignal):

"""Coroutine-based signal implementation.

To connect a callback to a signal, use any list method.

Signals are fired using the :meth:`send` coroutine, which takes named

arguments.

"""

def __init__(self, app):

super().__init__()

self._app = app

klass = self.__class__

self._name = klass.__module__ + ':' + klass.__qualname__

self._pre = app.on_pre_signal

self._post = app.on_post_signal

@asyncio.coroutine

def send(self, *args, **kwargs):

"""

Sends data to all registered receivers.

"""

ordinal = None

debug = self._app._debug

if debug:

ordinal = self._pre.ordinal()

yield from self._pre.send(ordinal, self._name, *args, **kwargs)

yield from self._send(*args, **kwargs)

if debug:

yield from self._post.send(ordinal, self._name, *args, **kwargs)

class DebugSignal(BaseSignal):

@asyncio.coroutine

def send(self, ordinal, name, *args, **kwargs):

yield from self._send(ordinal, name, *args, **kwargs)

class PreSignal(DebugSignal):

def __init__(self):

super().__init__()

self._counter = count(1)

def ordinal(self):

return next(self._counter)

class PostSignal(DebugSignal):

pass