from weakref import ref

__all__ = ['EventHub', 'Signal']

class EventHub(object):

    def __init__(self):
        self._events = {}

    def copy(self):
        new = self.__class__()
        new._events = self._events.copy()
        return new

    def listen(self, signal, listener, attr=None, weak=True):
        if weak:
            listener = ref(listener)
        else:
            listener = lambda l=listener: l
        self._events.setdefault(signal, []).append((listener, attr))

    def send(self, signal, **kw):
        for listener, attr in self._events.get(signal, ()):
            l = listener()
            if l is not None:
                if attr is not None:
                    l = getattr(l, attr)
                l(**kw)
    
class _Signal(object):
    """
    Base event for all SQLObject events.

    In general the sender for these methods is the class, not the
    instance.
    """

    def __init__(self, class_name, bases, attrs):
        self.name = self.__name__ = class_name
        for name, value in attrs.items():
            setattr(self, name, value)

    def __repr__(self):
        return '<Signal:%s>' % (self.name)

Signal = _Signal('Signal', (), {})