workflow.php

<?php
require 'vendor/autoload.php';

use Psr\Log\LoggerInterface;
use Symfony\Component\EventDispatcher\EventDispatcher;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\Workflow\DefinitionBuilder;
use Symfony\Component\Workflow\Event\Event;
use Symfony\Component\Workflow\Event\GuardEvent;
use Symfony\Component\Workflow\EventListener\AuditTrailListener;
use Symfony\Component\Workflow\Exception\NotEnabledTransitionException;
use Symfony\Component\Workflow\MarkingStore\MethodMarkingStore;
use Symfony\Component\Workflow\StateMachine;
use Symfony\Component\Workflow\SupportStrategy\InstanceOfSupportStrategy;
use Symfony\Component\Workflow\Tests\EventListener\Logger;
use Symfony\Component\Workflow\Transition;
use Symfony\Component\Workflow\TransitionBlocker;

class BlogPost
{
    protected $id;
    protected $subject;
    protected $title;

    /**
     * @return mixed
     */
    public function getTitle()
    {
        return $this->title;
    }

    /**
     * @param mixed $title
     */
    public function setTitle($title): void
    {
        $this->title = $title;
    }
    protected $currentState = 'draft';

    /**
     * @return mixed
     */
    public function getSubject()
    {
        return $this->subject;
    }

    /**
     * @param mixed $subject
     */
    public function setSubject($subject): void
    {
        $this->subject = $subject;
    }

    /**
     * BlogPost constructor.
     * @param $id
     */
    public function __construct($id)
    {
        $this->id = $id;
    }

    /**
     * @return mixed
     */
    public function getId()
    {
        return $this->id;
    }

    /**
     * @param mixed $id
     */
    public function setId($id): void
    {
        $this->id = $id;
    }

    /**
     * @return string
     */
    public function getCurrentState(): string
    {
        return $this->currentState;
    }

    /**
     * @param string $currentState
     */
    public function setCurrentState(string $currentState): void
    {
        var_dump('setting: '.$currentState);
        $this->currentState = $currentState;
    }
}

class WorkflowLogger implements EventSubscriberInterface
{
    private $logger;

    public function __construct(LoggerInterface $logger)
    {
        $this->logger = $logger;
    }

    public function guardPublish(GuardEvent $event)
    {
        var_dump('attempting transition', [
            'current' => $event->getSubject()->getCurrentState(),
            'transition' => $event->getTransition()->getName(),
        ]);

        /** @var BlogPost $post */
        $post = $event->getSubject();
        $title = $post->getTitle();

        if (empty($title)) {
            $event->addTransitionBlocker(new TransitionBlocker('Blocked', 0, ['bob' => 'hello']));
            $event->setBlocked(true);
            return;
        }
    }

    public static function getSubscribedEvents()
    {
        return [
            'workflow.blog_publishing.guard.publish' => ['guardPublish'],
        ];
    }
}

$definitionBuilder = new DefinitionBuilder();
$definition = $definitionBuilder->addPlaces(['draft', 'reviewed', 'rejected', 'published'])
    // Transitions are defined with a unique name, an origin place and a destination place
    ->addTransition(new Transition('to_review', 'draft', 'reviewed'))
    ->addTransition(new Transition('publish', 'reviewed', 'published'))
    ->addTransition(new Transition('reject', 'reviewed', 'rejected'))
    ->build()
;

$singleState = true; // true if the subject can be in only one state at a given time
$property = 'currentState'; // subject property name where the state is stored
$marking = new MethodMarkingStore($singleState, $property);

$logger = new Logger();

$ed = new EventDispatcher();
$ed->addSubscriber(new AuditTrailListener($logger));
$ed->addSubscriber(new WorkflowLogger($logger));

$workflow = new StateMachine($definition, $marking, $ed, 'blog_publishing');

$registry = new \Symfony\Component\Workflow\Registry();
$registry->addWorkflow($workflow, new InstanceOfSupportStrategy(BlogPost::class));

$blogPost = new BlogPost(19);
$workflow = $registry->get($blogPost);

$workflow->apply($blogPost, 'to_review'); // $blogPost is now in place "reviewed"

try{
//    $workflow->apply($blogPost, 'publish'); // $blogPost is now in place "reviewed"
} catch(NotEnabledTransitionException $e) {
    foreach($e->getTransitionBlockerList() as $blocker) {
        var_dump($blocker);
    }
}

var_dump($logger->logs);