"""
Mediator Design Pattern
Intent: Lets you reduce chaotic dependencies between objects. The pattern
restricts direct communications between the objects and forces them to
collaborate only via a mediator object.
"""
from __future__ import annotations
from abc import ABC
class Mediator(ABC):
"""
The Mediator interface declares a method used by components to notify the
mediator about various events. The Mediator may react to these events and
pass the execution to other components.
"""
def notify(self, sender: object, event: str) -> None:
pass
class ConcreteMediator(Mediator):
def __init__(self, component1: Component1, component2: Component2) -> None:
self._component1 = component1
self._component1.mediator = self
self._component2 = component2
self._component2.mediator = self
def notify(self, sender: object, event: str) -> None:
if event == "A":
print("Mediator reacts on A and triggers following operations:")
self._component2.do_c()
elif event == "D":
print("Mediator reacts on D and triggers following operations:")
self._component1.do_b()
self._component2.do_c()
class BaseComponent:
"""
The Base Component provides the basic functionality of storing a mediator's
instance inside component objects.
"""
def __init__(self, mediator: Mediator = None) -> None:
self._mediator = mediator
@property
def mediator(self) -> Mediator:
return self._mediator
@mediator.setter
def mediator(self, mediator: Mediator) -> None:
self._mediator = mediator
"""
Concrete Components implement various functionality. They don't depend on other
components. They also don't depend on any concrete mediator classes.
"""
class Component1(BaseComponent):
def do_a(self) -> None:
print("Component 1 does A.")
self.mediator.notify(self, "A")
def do_b(self) -> None:
print("Component 1 does B.")
self.mediator.notify(self, "B")
class Component2(BaseComponent):
def do_c(self) -> None:
print("Component 2 does C.")
self.mediator.notify(self, "C")
def do_d(self) -> None:
print("Component 2 does D.")
self.mediator.notify(self, "D")
if __name__ == "__main__":
c1 = Component1()
c2 = Component2()
mediator = ConcreteMediator(c1, c2)
print("Client triggers operation A.")
c1.do_a()
print("\n", end="")
print("Client triggers operation D.")
c2.do_d()