import weakref

from django.dispatch import saferef

WEAKREF_TYPES = (weakref.ReferenceType, saferef.BoundMethodWeakref)

def _make_id(target):

    if hasattr(target, 'im_func'):

        return (id(target.im_self), id(target.im_func))

    return id(target)

class Signal(object):

    """

    Base class for all signals

    Internal attributes:

        receivers

            { receriverkey (id) : weakref(receiver) }

    """

    def __init__(self, providing_args=None):

        """

        Create a new signal.

        providing_args

            A list of the arguments this signal can pass along in a send() call.

        """

        self.receivers = []

        if providing_args is None:

            providing_args = []

        self.providing_args = set(providing_args)

    def connect(self, receiver, sender=None, weak=True, dispatch_uid=None):

        """

        Connect receiver to sender for signal.

        Arguments:

            receiver

                A function or an instance method which is to receive signals.

                Receivers must be hashable objects.

                if weak is True, then receiver must be weak-referencable (more

                precisely saferef.safeRef() must be able to create a reference

                to the receiver).

                Receivers must be able to accept keyword arguments.

                If receivers have a dispatch_uid attribute, the receiver will

                not be added if another receiver already exists with that

                dispatch_uid.

            sender

                The sender to which the receiver should respond Must either be

                of type Signal, or None to receive events from any sender.

            weak

                Whether to use weak references to the receiver By default, the

                module will attempt to use weak references to the receiver

                objects. If this parameter is false, then strong references will

                be used.

            dispatch_uid

                An identifier used to uniquely identify a particular instance of

                a receiver. This will usually be a string, though it may be

                anything hashable.

        """

        from django.conf import settings

        # If DEBUG is on, check that we got a good receiver

        if settings.DEBUG:

            import inspect

            assert callable(receiver), "Signal receivers must be callable."

            # Check for **kwargs

            # Not all callables are inspectable with getargspec, so we'll

            # try a couple different ways but in the end fall back on assuming

            # it is -- we don't want to prevent registration of valid but weird

            # callables.

            try:

                argspec = inspect.getargspec(receiver)

            except TypeError:

                try:

                    argspec = inspect.getargspec(receiver.__call__)

                except (TypeError, AttributeError):

                    argspec = None

            if argspec:

                assert argspec[2] is not None, \

                    "Signal receivers must accept keyword arguments (**kwargs)."

        if dispatch_uid:

            lookup_key = (dispatch_uid, _make_id(sender))

        else:

            lookup_key = (_make_id(receiver), _make_id(sender))

        if weak:

            receiver = saferef.safeRef(receiver, onDelete=self._remove_receiver)

        for r_key, _ in self.receivers:

            if r_key == lookup_key:

                break

        else:

            self.receivers.append((lookup_key, receiver))

    def disconnect(self, receiver=None, sender=None, weak=True, dispatch_uid=None):

        """

        Disconnect receiver from sender for signal.

        If weak references are used, disconnect need not be called. The receiver

        will be remove from dispatch automatically.

        Arguments:

            receiver

                The registered receiver to disconnect. May be none if

                dispatch_uid is specified.

            sender

                The registered sender to disconnect

            weak

                The weakref state to disconnect

            dispatch_uid

                the unique identifier of the receiver to disconnect

        """

        if dispatch_uid:

            lookup_key = (dispatch_uid, _make_id(sender))

        else:

            lookup_key = (_make_id(receiver), _make_id(sender))

        for index in xrange(len(self.receivers)):

            (r_key, _) = self.receivers[index]

            if r_key == lookup_key:

                del self.receivers[index]

                break

    def send(self, sender, **named):

        """

        Send signal from sender to all connected receivers.

        If any receiver raises an error, the error propagates back through send,

        terminating the dispatch loop, so it is quite possible to not have all

        receivers called if a raises an error.

        Arguments:

            sender

                The sender of the signal Either a specific object or None.

            named

                Named arguments which will be passed to receivers.

        Returns a list of tuple pairs [(receiver, response), ... ].

        """

        responses = []

        if not self.receivers:

            return responses

        for receiver in self._live_receivers(_make_id(sender)):

            response = receiver(signal=self, sender=sender, **named)

            responses.append((receiver, response))

        return responses

    def send_robust(self, sender, **named):

        """

        Send signal from sender to all connected receivers catching errors.

        Arguments:

            sender

                The sender of the signal Can be any python object (normally one

                registered with a connect if you actually want something to

                occur).

            named

                Named arguments which will be passed to receivers. These

                arguments must be a subset of the argument names defined in

                providing_args.

        Return a list of tuple pairs [(receiver, response), ... ]. May raise

        DispatcherKeyError.

        if any receiver raises an error (specifically any subclass of

        Exception), the error instance is returned as the result for that

        receiver.

        """

        responses = []

        if not self.receivers:

            return responses

        # Call each receiver with whatever arguments it can accept.

        # Return a list of tuple pairs [(receiver, response), ... ].

        for receiver in self._live_receivers(_make_id(sender)):

            try:

                response = receiver(signal=self, sender=sender, **named)

            except Exception, err:

                responses.append((receiver, err))

            else:

                responses.append((receiver, response))

        return responses

    def _live_receivers(self, senderkey):

        """

        Filter sequence of receivers to get resolved, live receivers.

        This checks for weak references and resolves them, then returning only

        live receivers.

        """

        none_senderkey = _make_id(None)

        receivers = []

        for (receiverkey, r_senderkey), receiver in self.receivers:

            if r_senderkey == none_senderkey or r_senderkey == senderkey:

                if isinstance(receiver, WEAKREF_TYPES):

                    # Dereference the weak reference.

                    receiver = receiver()

                    if receiver is not None:

                        receivers.append(receiver)

                else:

                    receivers.append(receiver)

        return receivers

    def _remove_receiver(self, receiver):

        """

        Remove dead receivers from connections.

        """

        to_remove = []

        for key, connected_receiver in self.receivers:

            if connected_receiver == receiver:

                to_remove.append(key)

        for key in to_remove:

            for idx, (r_key, _) in enumerate(self.receivers):

                if r_key == key:

                    del self.receivers[idx]