import traceback
from Delegator import Delegator

class NamedDelegator(Delegator):
    "A bit of infrastructure..."
    def __init__(self, name):
        Delegator.__init__(self)
        self.name = name

    def _forward(self, to):
        return self.name + ' -> ' + to

    def _catch(self):
        return self.name


class Catcher(NamedDelegator):
    "Just catches everything"
    forwarded = intercepted = quietly_forwarded = quietly_intercepted = \
                __call__ = NamedDelegator._catch

class Passer(NamedDelegator):
    "Just forwards everything"
    def forwarded(self):
        return self._forward(self.delegate.forwarded())

    def intercepted(self):
        return self._forward(self.delegate.intercepted())

    # forwarding quietly means letting Delegator take care of it

class Interceptor(NamedDelegator):
    "Forwards or intercepts, according to method names"
    def forwarded(self):
        return self._forward(self.delegate.forwarded())

    quietly_intercepted = NamedDelegator._catch
    intercepted = NamedDelegator._catch
    __call__ = NamedDelegator._catch

class CallableDelegator(Delegator):
    def __call__(self, *args, **kwargs):
        return self.delegate.__call__(*args, **kwargs)

# Set up a chain
bottom = b0 = Catcher("Catcher")
b1 = Passer("Passer 1")
b1.setdelegate(b0)
b2 = Interceptor("Interceptor 2")
b2.setdelegate(b1)
top = b3 = Passer("Passer 3")
b3.setdelegate(b2)

# See what happens

print '"forwarded" is only implemented by the bottom ("Catcher"):'
print 'top.forwarded() =', top.forwarded()
print
print 'but "intercepted" is also implemented by b2 ("Interceptor 2"):'
print 'top.intercepted() =', top.intercepted()
print

print 'this is how it looks without printing the chains:'
print 'top.quietly_forwarded() =', top.quietly_forwarded()
print 'top.quietly_intercepted() =', top.quietly_intercepted()
print

print "now let's try something similar with __call__:"
Callable = CallableDelegator()
Callable.setdelegate(top)
print 'Callable() =', Callable()
NonCallable = Delegator()
NonCallable.setdelegate(top)
try:
    print 'NonCallable() =', NonCallable()
except:
    print
    traceback.print_exc()
print

print 'But this works!'
print 'NonCallable.delegate.__call__() =', NonCallable.delegate.__call__()