from typing import Optional

from behavioral.command.command import Command


class Invoker:
    """
    The Invoker is associated with one or several commands. It sends a request
    to the command.
    """

    _on_start: Optional[Command] = None
    _on_finish: Optional[Command] = None

    """Initialize commands."""

    def set_on_start(self, command: Command) -> None:
        self._on_start = command

    def set_on_finish(self, command: Command) -> None:
        self._on_finish = command

    def do_something_important(self) -> None:
        """
        The Invoker does not depend on concrete command or receiver classes. The
        Invoker passes a request to a receiver indirectly, by executing a
        command.
        """

        print("Invoker: Does anybody want something done before I begin?")
        if self._on_start:
            self._on_start.execute()

        print("Invoker: ...doing something really important...")

        print("Invoker: Does anybody want something done after I finish?")
        if self._on_finish:
            self._on_finish.execute()