class Subject {
  constructor() {
    this.observers = [];
  }

  subscribe(observer) {
    if (!observer || typeof observer.update !== 'function') return;
    this.observers.push(observer);
  }

  unsubscribe(observer) {
    this.observers = this.observers.filter(o => o !== observer);
  }

  unsubscribeAll() {
    this.observers = [];
  }

  notifySubscribers(source, ...others) {
    for (let observer of this.observers) {
      observer.update(source, ...others);
    }
  }
}


export { Subject };