export class AnEvent implements Observable {
	private readonly observers: Observer[];
	constructor() {
		this.observers = [];
	}
	subscribe(observer: Observer) {
		const index = this.observers.indexOf(observer);
		if (!~index) {
			this.observers.push(observer);
		}
	}
	unsubscribe(observer: Observer) {
		const index = this.observers.indexOf(observer);
		if (~this.observers.indexOf(observer)) {
			this.observers.splice(index, 1);
		}
	}
	notify() {
		for (const observer of this.observers) {
			observer();
		}
	}
}

interface Observable {
	subscribe(observer: () => void): void;
	unsubscribe(observer: () => void): void;
	notify(): void;
}

type Observer = () => void;