import typing


class StateBase:
    def __init__(self, owner: "FileSender", state_mgr: "StateManager"):
        self.owner = owner
        self.state_mgr = state_mgr


class StateManager:
    def __init__(self, owner, base_state_type):
        self.__owner = owner
        self.__base_state_type = base_state_type
        self.current_state: "FileSender_BaseState" = base_state_type(self.__owner, self)

    def transition_to(self, next_state_type: typing.Type["FileSender_BaseState"]):
        next_state = next_state_type(self.__owner, self)
        self.current_state = next_state


class FileSender_BaseState(StateBase):
    def on_event(self, msg):
        pass


class FileSender_Idle(FileSender_BaseState):
    def on_event(self, msg):
        self.owner.foo()


class FileSender_Sending(FileSender_BaseState):
    def on_event(self, msg):
        pass


class FileSender:
    def __init__(self):
        self._state_mgr = StateManager(self, FileSender_BaseState)
        self._state_mgr.transition_to(FileSender_Idle)

        self._state_mgr.current_state.on_event(None)

    def foo(self):
        pass