command.py

"""
	Command
	- a behavioral design pattern that turns a request into a stand-alone object that
	contains all information about the request. This transformation lets you pass requests
	as a method arguments, delay or queue a request’s execution, and support undoable operations.
"""
import abc


class Command(abc.ABC):

	@abc.abstractmethod
	def execute(self):
		pass


class SimpleCommand(Command):
	def __init__(self, payload):
		self._payload = payload

	def execute(self):
		print(f'SimpleCommand: I can do simple things like printing ({self._payload})')


class ComplexCommand(Command):
	def __init__(self, receiver, a, b):
		self._receiver = receiver
		self._a = a
		self._b = b

	def execute(self):
		print('ComplexCommand: Complex stuff should be done a receiver object', end='')
		self._receiver.do_something(self._a)
		self._receiver.do_something_else(self._b)


class Receiver:
	def do_something(self, a):
		print(f'\nReceiver: working on ({a}.)', end="")

	def do_something_else(self, b):
		print(f'\nReceiver: working on ({b}.)', end="")


class Invoker:
	_on_start = None
	_on_finish = None

	def set_on_start(self, command):
		self._on_start = command

	def set_on_finish(self, command):
		self._on_finish = command

	def operation(self):
		self._on_start.execute()
		self._on_finish.execute()


invoker = Invoker()
invoker.set_on_start(SimpleCommand('Say Hi!'))

receiver = Receiver()
invoker.set_on_finish(ComplexCommand(receiver, 'Send email', 'Save report'))

invoker.operation()