Chain of Responsibility in PHP

<?php

namespace RefactoringGuru\ChainOfResponsibility\RealWorld;

/**
 * The classic CoR pattern declares a single role for objects that make up a
 * chain, which is a Handler. In our example, let's differentiate between
 * middleware and a final application's handler, which is executed when a
 * request gets through all the middleware objects.
 *
 * The base Middleware class declares an interface for linking middleware
 * objects into a chain.
 */
abstract class Middleware
{
    /**
     * @var Middleware
     */
    private $next;

    /**
     * This method can be used to build a chain of middleware objects.
     */
    public function linkWith(Middleware $next): Middleware
    {
        $this->next = $next;

        return $next;
    }

    /**
     * Subclasses must override this method to provide their own checks. A
     * subclass can fall back to the parent implementation if it can't process a
     * request.
     */
    public function check(string $email, string $password): bool
    {
        if (!$this->next) {
            return true;
        }

        return $this->next->check($email, $password);
    }
}

/**
 * This Concrete Middleware checks whether a user with given credentials exists.
 */
class UserExistsMiddleware extends Middleware
{
    private $server;

    public function __construct(Server $server)
    {
        $this->server = $server;
    }

    public function check(string $email, string $password): bool
    {
        if (!$this->server->hasEmail($email)) {
            echo "UserExistsMiddleware: This email is not registered!\n";

            return false;
        }

        if (!$this->server->isValidPassword($email, $password)) {
            echo "UserExistsMiddleware: Wrong password!\n";

            return false;
        }

        return parent::check($email, $password);
    }
}

/**
 * This Concrete Middleware checks whether a user associated with the request
 * has sufficient permissions.
 */
class RoleCheckMiddleware extends Middleware
{
    public function check(string $email, string $password): bool
    {
        if ($email === "admin@example.com") {
            echo "RoleCheckMiddleware: Hello, admin!\n";

            return true;
        }
        echo "RoleCheckMiddleware: Hello, user!\n";

        return parent::check($email, $password);
    }
}

/**
 * This Concrete Middleware checks whether there are too many failed login
 * requests.
 */
class ThrottlingMiddleware extends Middleware
{
    private $requestPerMinute;

    private $request;

    private $currentTime;

    public function __construct(int $requestPerMinute)
    {
        $this->requestPerMinute = $requestPerMinute;
        $this->currentTime = time();
    }

    /**
     * Please, note that the parent::check call can be inserted both at the
     * beginning of this method and at the end.
     *
     * This gives much more flexibility than a simple loop over all middleware
     * objects. For instance, a middleware can change the order of checks by
     * running its check after all the others.
     */
    public function check(string $email, string $password): bool
    {
        if (time() > $this->currentTime + 60) {
            $this->request = 0;
            $this->currentTime = time();
        }

        $this->request++;

        if ($this->request > $this->requestPerMinute) {
            echo "ThrottlingMiddleware: Request limit exceeded!\n";
            die();
        }

        return parent::check($email, $password);
    }
}

/**
 * This is an application's class that acts as a real handler. The Server class
 * uses the CoR pattern to execute a set of various authentication middleware
 * before launching some business logic associated with a request.
 */
class Server
{
    private $users = [];

    /**
     * @var Middleware
     */
    private $middleware;

    /**
     * The client can configure the server with a chain of middleware objects.
     */
    public function setMiddleware(Middleware $middleware): void
    {
        $this->middleware = $middleware;
    }

    /**
     * The server gets the email and password from the client and sends the
     * authorization request to the middleware.
     */
    public function logIn(string $email, string $password): bool
    {
        if ($this->middleware->check($email, $password)) {
            echo "Server: Authorization has been successful!\n";

            // Do something useful for authorized users.

            return true;
        }

        return false;
    }

    public function register(string $email, string $password): void
    {
        $this->users[$email] = $password;
    }

    public function hasEmail(string $email): bool
    {
        return isset($this->users[$email]);
    }

    public function isValidPassword(string $email, string $password): bool
    {
        return $this->users[$email] === $password;
    }
}

/**
 * The client code.
 */
$server = new Server();
$server->register("admin@example.com", "admin_pass");
$server->register("user@example.com", "user_pass");

// All middleware are chained. The client can build various configurations of
// chains depending on its needs.
$middleware = new ThrottlingMiddleware(2);
$middleware
    ->linkWith(new UserExistsMiddleware($server))
    ->linkWith(new RoleCheckMiddleware());

// The server gets a chain from the client code.
$server->setMiddleware($middleware);

// ...

do {
    echo "\nEnter your email:\n";
    $email = readline();
    echo "Enter your password:\n";
    $password = readline();
    $success = $server->logIn($email, $password);
} while (!$success);

Enter your email:
asd
Enter your password:
123
UserExistsMiddleware: This email is not registered!

Enter your email:
admin@example.com
Enter your password:
wrong
UserExistsMiddleware: Wrong password!

Enter your email:
admin@example.com
Enter your password:
letmein
ThrottlingMiddleware: Request limit exceeded!



Enter your email:
admin@example.com
Enter your password:
admin_pass
RoleCheckMiddleware: Hello, admin!
Server: Authorization has been successful!