"""
File:    signal.py
Author:  Thiago Marcos P. Santos
Created: August 28, 2008

Purpose: A signal/slot implementation
"""

from weakref import WeakValueDictionary


class Signal(object):
    def __init__(self):
        self.__slots = WeakValueDictionary()

    def __call__(self, *args, **kargs):
        for key in self.__slots:
            func, _ = key
            func(self.__slots[key], *args, **kargs)

    def connect(self, slot):
        key = (slot.im_func, id(slot.im_self))
        self.__slots[key] = slot.im_self

    def disconnect(self, slot):
        key = (slot.im_func, id(slot.im_self))
        if key in self.__slots:
            self.__slots.pop(key)

    def clear(self):
        self.__slots.clear()


# Sample usage:
class Model(object):
    def __init__(self, value):
        self.__value = value
        self.changed = Signal()

    def set_value(self, value):
        self.__value = value
        self.changed() # Emit signal

    def get_value(self):
        return self.__value


class View(object):
    def __init__(self, model):
        self.model = model
        model.changed.connect(self.model_changed)

    def model_changed(self):
        print "New value:", self.model.get_value()


model = Model(10)
view1 = View(model)
view2 = View(model)
view3 = View(model)

model.set_value(20)

del view1
model.set_value(30)

model.changed.clear()
model.set_value(40)