PHP observer design pattern example

index.php

<?php


/**
 *
 */
interface HandleInterface
{
    /**
     * @param Content $content
     * @return mixed
     */
    public function handle(Content $content);
}

/**
 *
 */
interface Content
{
    /**
     * @return string
     */
    public function getContent(): string;

    /**
     * @return string
     */
    public function getUser(): string;
}

/**
 *
 */
interface Notification
{
    /**
     * @param HandleInterface $handle
     * @return $this
     */
    public function attach(HandleInterface $handle): self;

    /**
     * @param HandleInterface $handle
     * @return $this
     */
    public function detach(HandleInterface $handle): self;

    /**
     * @return void
     */
    public function notify(): void;
}

/**
 *
 */
class Post implements HandleInterface
{

    /**
     * @param Content $content
     * @return void
     */
    public function handle(Content $content): void
    {

        echo sprintf('post =>user: %s,content: %s',
            $content->getUser(),
            $content->getContent()
        );

    }
}

/**
 *
 */
class Comment implements HandleInterface
{

    /**
     * @param Content $content
     * @return mixed
     */
    public function handle(Content $content)
    {

        echo sprintf('comment =>user: %s,content: %s',
            $content->getUser(),
            $content->getContent()
        );
    }
}

/**
 *
 */
class Notify implements Notification, Content
{

    /**
     * @var SplObjectStorage|HandleInterface[] $notifications
     */
    private SplObjectStorage $notifications;

    /**
     *
     */
    public function __construct()
    {

        $this->notifications = new SplObjectStorage();
    }

    /**
     * @return string
     */
    public function getContent(): string
    {
        return 'user has notification';
    }

    /**
     * @return string
     */
    public function getUser(): string
    {
        return 'admin';
    }

    /**
     * @return $this
     */
    public function attach(HandleInterface $handle): Notification
    {
        $this->notifications->attach($handle);
        return $this;
    }

    /**
     * @return $this
     */
    public function detach(HandleInterface $handle): Notification
    {
        $this->notifications->detach($handle);
        return $this;
    }

    /**
     * @return void
     */
    public function notify(): void
    {
        foreach ($this->notifications as $notification) {
            $notification->handle($this);
        }
    }
}


$notify = new Notify();

$notify
    ->attach(new Post())
    ->attach(new Comment());

$notify->notify();