Run ReactPHP Event Loop with database query and return Promise

LookupService.php

<?php

namespace Acme\FooApplication\OfferLetter;

use React\EventLoop\Timer\Timer;
use React\Promise\Deferred;
use Acme\Foo\Domain\Model\Offer\OfferId;
use React\EventLoop\Factory;
use Acme\Foo\Infrastructure\Projection\Mongo\OfferOverviewFinder;

class OfferLetterLookup
{
    /** @var OfferOverviewFinder */
    private $offerOverviewFinder;

    /**
     * OfferLetterLookup constructor.
     * @param OfferOverviewFinder $offerOverviewFinder
     */
    public function __construct(OfferOverviewFinder $offerOverviewFinder)
    {
        $this->offerOverviewFinder = $offerOverviewFinder;
    }

    public function lookup(OfferId $offerId, Deferred $deferred)
    {
        $i = 0;
        
        $loop = Factory::create();
        $loop->addPeriodicTimer(2, function(Timer $timer) use (&$i, $deferred, $offerId) {
            $deferred->notify($i++);
            
            $offer = $this->offerOverviewFinder->ofOfferId($offerId);

            if (isset($offer['offerLetterId'])) {
                $deferred->resolve($offer['offerLetterId']);
                $timer->cancel();
            }            

            if ($i >= 10) {
                $timer->cancel();
                $deferred->reject();
            }
        });

        $loop->run();

        return $deferred;
    }
}

OfferController.php

<?php

namespace Acme\Intranet\Infrastructure\Symfony\IntranetBundle\Controller;

class OfferController extends Controller
{
    public function lookupOfferLetterAction(string $offerId)
    {
        $data = ['offerLetterId' => null];
        
        $query = LookupOfferLetterQuery::with(OfferId::fromString($offerId));

        $offerList = $this->get('prooph_service_bus.intranet_query_bus')->dispatch($query);
        $offerList
            ->then(
                function($offerLetterId) use (&$data) {
                    $data['offerLetterId'] = (string)$offerLetterId;
                }
            );

        return new JsonResponse($data);
    }
}

view.html.twig

{% block content %}

    <script type="text/javascript">
        $(document).ready(function() {
            {% if details.offerLetterId is null %}
            function isUUID(string){
                return RegExp("^[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{4}-[0-9a-fA-F]{12}$").test(string);
            }

            $.ajax({
                type: "POST",
                dataType: "json",
                url: '{{ path('sps_intranet_offer_lookup_offer_letter', {'offerId': details.offerId }) }}',
                timeout: 60000,
                success: function(data) {

                    $('#lookup-offer-letter').hide();

                    if (data.hasOwnProperty('offerLetterId')) {
                        if (isUUID(data['offerLetterId'])) {
                            $('#advanced-offer-options').show();

                            return true;
                        }
                    }

                    alert('{{ 'lookup_offer_letter_error'|trans }}');
                },
                error: function(jqXHR, textStatus) {
                    $('#lookup-offer-letter').hide();

                    if (textStatus === 'timeout') {
                        alert('{{ 'lookup_offer_letter_error'|trans }}');
                    }
                }
            });
            {% endif %}
    </script>

{% endblock %}

And by the way, you should use array by reference in closure:

function($offerLetterId) use ($data) {
    $data['offerLetterId'] = (string)$offerLetterId;
}

This code doesn't change an array outside the closure, only the copy inside of it.

Thank you very much @seregazhuk, @rpkamp. I added your changes!

When running the EventLoop locally on Apache the process will block all other HTTP processes.
Is this an expected behaviour? Do I need sockets? Is "multi threading" possible with Docker instead?

Forgive my ignorance on this topic.