class TimekeeperModel:
    """
    Model of an ideal timekeeper
    """

    def __init__(self):
        self.system_model = None

        self.__tracking = False
        self.__start_time = 0.0
        self.__stop_time = 0.0

    def get_time(self):
        """
        Returns the elapsed time in seconds
        """
        return self.__stop_time - self.__start_time

    def attach_system_model(self, system_model):
        """
        Attaches the system model to the state retention technique
        :param system_model: the system model
        """
        from ScEpTIC.emulator.energy.system_energy_model import SystemEnergyModel

        if not isinstance(system_model, SystemEnergyModel):
            raise ConfigurationException(f"Invalid class {system_model.__class__.__name__} for system_model. SystemEnergyModel required!")

        self.system_model = system_model

    def start_tracking(self):
        """
        Sets the timekeeper to start tracking time
        """
        if not self.__tracking:
            self.__tracking = True
            self.__start_time = self.system_model.get_simulation_time()

    def stop_tracking(self):
        """
        Sets the timekeeper to stop tracking time
        """
        self.__tracking = False
        self.__stop_time = self.system_model.get_simulation_time()