import weakref

try:

    set

except NameError:

    from sets import Set as set # Python 2.3 fallback

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):

        """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

        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.

        returns None

        """

        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

        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

        disconnect reverses the process of connect.

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

          The receiver will be remove from dispatch automatically.

        returns None

        """

        if dispatch_uid:

            lookup_key = (dispatch_uid, _make_id(sender))

        else:

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

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

            if r_key == lookup_key:

                del self.receivers[idx]

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

        """Send signal from sender to all connected receivers.

        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), ... ].

        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.

        """

        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

        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)

        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:

                        yield receiver

                else:

                    yield receiver

    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]