from random import randrange
from typing import List, Optional

from behavioral.observer.observer import Observer
from behavioral.observer.subject import Subject


class ConcreteSubject(Subject):
    """
    The Subject owns some important state and notifies observers when the state
    changes.
    """

    """
    For the sake of simplicity, the Subject's state, essential to all
    subscribers, is stored in this variable.
    """
    _state: Optional[int] = None

    """
    List of subscribers. In real life, the list of subscribers can be stored
    more comprehensively (categorized by event type, etc.).
    """
    _observers: List[Observer] = []

    @property
    def state(self) -> int:
        return self._state

    def attach(self, observer: Observer) -> None:
        print("Subject: Attached an observer.")
        self._observers.append(observer)

    def detach(self, observer: Observer) -> None:
        self._observers.remove(observer)

    """
    The subscription management methods.
    """

    def notify(self) -> None:
        """
        Trigger an update in each subscriber.
        """
        print("Subject: Notifying observers...")
        for observer in self._observers:
            observer.update(self)

    def some_business_logic(self) -> None:
        """
        Usually, the subscription logic is only a fraction of what a Subject can
        really do. Subjects commonly hold some important business logic, that
        triggers a notification method whenever something important is about to
        happen (or after it).
        """

        print("\nSubject: I'm doing something important.")
        self._state = randrange(0, 10)

        print(f"Subject: My state has just changed to: {self._state}")
        self.notify()