Fluent Router in PHP

demo.php

engine()
    ->if(2)->then(function () { echo 'then'; })
    ->elif(0)->then()
    ->else()
;

engine.php

function engine() {
    $engine = new FluentRouter;

    $then = function ($callable) use ($engine) {
        $callable();
        return $engine;
    };

    $if = function ($condition) use (&$if, $then) {
        $router = new FluentRouter;
        if ($condition) {
            $router->addCallback('then', $then);
        } else {
            $router->addCallback('elif', $if);
            $router->addCallback('else', $then);
        }
        return $router;
    };

    $engine->addCallback('if', $if);
    return $engine;
}

FluentRouter.php

<?php

class FluentRouter
{
    const DEADEND_EXCEPTION = 1;
    const DEADEND_RETRY     = 2;
    const DEADEND_BLACKHOLE = 3;

    public function __construct(array $callbacks = [], $deadend = null)
    {
        $this->callbacks = $callbacks;
        $this->deadend   = $deadend;
    }

    public function addCallback($method, callable $callback)
    {
        $this->callbacks[$method] = $callback;
    }

    public function removeCallback($method)
    {
        unset($this->callbacks[$method]);
    }

    public function __call($method, $arguments)
    {
        if (array_key_exists($method, $this->callbacks)) {
            $callback = $this->callbacks[$method];
            return $callback(...$arguments);
        } else {
            switch ($this->deadend) {
            case static::DEADEND_EXCEPTION:
                throw new \BadMethodException($method);
            case static::DEADEND_BLACKHOLE:
                return new static;
            case static::DEADEND_RETRY:
            default:
                return $this;
            }
        }
        }
    }

    // PROTECTED API

    protected $callbacks;
    protected $deadend;
}