Card.php

<?php

namespace Hp\Patterns\Observer;

use SplObjectStorage;
use SplSubject;
use SplObserver;

class Card implements SplSubject
{
    private SplObjectStorage $observers;

    private float $money = 0;

    public function __construct()
    {
        $this->observers = new SplObjectStorage();
    }

    public function attach(SplObserver $observer): void
    {
        $this->observers->attach($observer);
    }

    public function detach(SplObserver $observer): void
    {
        $this->observers->detach($observer);
    }

    public function deposit(float $money): void
    {
        $this->money += $money;
        $this->notify();
    }

    public function getAmount(): float
    {
        return $this->money;
    }

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