import { isMainThread, SynStart, SynEnd, Syc } from "@kit.ArkTS";

interface Observer {

update(message: string): void;

}

interface Subject {

registerObserver(observer: Observer): void;

removeObserver(observer: Observer): void;

notifyObservers(message: string): void;

}

class ConcreteSubject implements Subject {

private readonly lock = new Syc();

private readonly observers: Observer[] = [];

private size = 0;

registerObserver(observer: Observer): void {

SynStart(this.lock);

this.synchronizeMethod1(observer);

SynEnd(this.lock);

}

removeObserver(observer: Observer): void {

SynStart(this.lock);

this.synchronizeMethod2(observer);

SynEnd(this.lock);

}

notifyObservers(message: string): void {

let snapshot: Observer[];

SynStart(this.lock);

snapshot = [...this.observers];

SynEnd(this.lock);

for (const observer of snapshot) {

if (observer) {

setTimeout(() => observer.update(message), 0);

}

}

}

stateChanged(newState: string): void {

console.log(`Subject state changed to: ${newState}`);

this.notifyObservers(newState);

}

private synchronizeMethod1(observer: Observer): void {

this.observers.push(observer);

this.size++;

}

private synchronizeMethod2(observer: Observer): void {

const index = this.observers.indexOf(observer);

if (index !== -1) {

this.observers.splice(index, 1);

this.size--;

}

}

}

class ConcreteObserver implements Observer {

private readonly observerName: string;

constructor(name: string) {

this.observerName = name;

}

update(message: string): void {

console.log(`${this.observerName} received message: ${message}`);

}

}

class ObserverPatternExample {

static main(): void {

const subject = new ConcreteSubject();

const observer1 = new ConcreteObserver("Observer 1");

const observer2 = new ConcreteObserver("Observer 2");

subject.registerObserver(observer1);

subject.registerObserver(observer2);

subject.stateChanged("New state!");

subject.removeObserver(observer1);

subject.stateChanged("Another new state!");

}

}

ObserverPatternExample.main();

if (isMainThread()) {

// You can put the entry of your code here to test.

}