Middleware Pipeline Designs

0.mutable.php

<?php

declare(strict_types=1);

interface Context {}

interface Handler
{
    public function handle(object $message, Context $context): void;
}

interface Middleware
{
    public function process(object $message, Context $context, Handler $next): void;
}

final class Pipeline implements Handler
{
    private int $offset = 0;

    /**
     * @param non-empty-list<Middleware> $middlewareList
     */
    public function __construct(
        private readonly Handler $handler,
        private readonly array $middlewareList,
    ) {}

    public function handle(object $message, Context $context): void
    {
        $middleware = $this->middlewareList[$this->offset] ?? null;

        if ($middleware === null) {
            $this->handler->handle($message, $context);

            return;
        }

        ++$this->offset; // мутация

        $middleware->process($message, $context, $this);
    }
}

1.immutable.php

<?php

interface Context {}

interface Handler
{
    public function handle(object $message, Context $context): void;
}

interface Middleware
{
    public function process(object $message, Context $context, Handler $next): void;
}

final readonly class MiddlewareHandler implements Handler
{
    public function __construct(
        private Middleware $middleware,
        private Handler $handler,
    ) {}

    public function handle(object $message, Context $context): void
    {
        $this->middleware->process($message, $context, $this->handler);
    }
}

function stackMiddleware(Handler $handler, Middleware ...$middlewareList): Handler
{
    foreach (array_reverse($middlewareList) as $middleware) {
        $handler = new MiddlewareHandler($middleware, $handler);
    }

    return $handler;
}