from abc import ABC, abstractmethod

from behavioral.observer.observer import Observer


class Subject(ABC):
    """
    The Subject interface declares a set of methods for managing subscribers.
    """

    @property
    @abstractmethod
    def state(self) -> int:
        pass

    @abstractmethod
    def attach(self, observer: Observer) -> None:
        """
        Attach an observer to the subject.
        """
        pass

    @abstractmethod
    def detach(self, observer: Observer) -> None:
        """
        Detach an observer to the subject.
        """
        pass

    @abstractmethod
    def notify(self) -> None:
        """
        Notify all observers about an event.
        """
        pass