3.4. Mediator

All components (called Colleague) are only coupled to theMediatorInterface and it is a good thing because in OOP, one good friendis better than many. This is the key-feature of this pattern.

MediatorInterface.php

Mediator.php

<?php
 
namespace DesignPatterns\Behavioral\Mediator;
 
/**
 * Mediator is the concrete Mediator for this design pattern
 *
 * In this example, I have made a "Hello World" with the Mediator Pattern
 */
class Mediator implements MediatorInterface
{
    /**
     * @var Subsystem\Server
     */
    private $server;
 
    /**
     * @var Subsystem\Database
     */
    private $database;
 
    /**
     * @var Subsystem\Client
     */
    private $client;
 
    /**
     * @param Subsystem\Database $database
     * @param Subsystem\Server $server
     */
    public function __construct(Subsystem\Database $database, Subsystem\Client $client, Subsystem\Server $server)
    {
        $this->database = $database;
        $this->server = $server;
        $this->client = $client;
 
        $this->database->setMediator($this);
        $this->server->setMediator($this);
        $this->client->setMediator($this);
    }
 
    public function makeRequest()
    {
        $this->server->process();
    }
 
    public function queryDb(): string
    {
        return $this->database->getData();
    }
 
    /**
     * @param string $content
     */
    public function sendResponse($content)
    {
        $this->client->output($content);
    }
}

Subsystem/Client.php

<?php
namespace DesignPatterns\Behavioral\Mediator\Subsystem;
 
use DesignPatterns\Behavioral\Mediator\Colleague;
 
/**
 * Client is a client that makes requests and gets the response.
 */
class Client extends Colleague
{
    public function request()
    {
        $this->mediator->makeRequest();
    }
 
    public function output(string $content)
    {
        echo $content;
    }
}

Subsystem/Database.php

<?php
 
namespace DesignPatterns\Behavioral\Mediator\Subsystem;
 
use DesignPatterns\Behavioral\Mediator\Colleague;
 
class Server extends Colleague
{
    public function process()
    {
        $data = $this->mediator->queryDb();
        $this->mediator->sendResponse(sprintf("Hello %s", $data));
    }

Tests/MediatorTest.php