PHP中的事件系统：如何实现观察者模式解耦组件

// 事件接口
interface EventInterface {
    public function getData();
}

// 具体的事件类
class UserRegisteredEvent implements EventInterface {
    private $userId;

    public function __construct(int $userId) {
        $this->userId = $userId;
    }

    public function getData() {
        return ['userId' => $this->userId];
    }
}

// 观察者接口
interface ObserverInterface {
    public function update(EventInterface $event);
}

// 具体的观察者类
class SendWelcomeEmailObserver implements ObserverInterface {
    public function update(EventInterface $event) {
        $data = $event->getData();
        // 实际发送邮件的逻辑
        echo "Sending welcome email to user: " . $data['userId'] . PHP_EOL;
    }
}

// 主题类
class Subject {
    private $observers = [];

    public function attach(ObserverInterface $observer) {
        $this->observers[] = $observer;
    }

    public function detach(ObserverInterface $observer) {
        $key = array_search($observer, $this->observers, true);
        if ($key !== false) {
            unset($this->observers[$key]);
        }
    }

    public function notify(EventInterface $event) {
        foreach ($this->observers as $observer) {
            $observer->update($event);
        }
    }
}

// 使用示例
$subject = new Subject();
$sendWelcomeEmailObserver = new SendWelcomeEmailObserver();
$subject->attach($sendWelcomeEmailObserver);

$userRegisteredEvent = new UserRegisteredEvent(123);
$subject->notify($userRegisteredEvent);