NodeRouteContext.php

<?php

namespace Drupal\node\ContextProvider;

use Drupal\Core\Cache\CacheableMetadata;
use Drupal\Core\Plugin\Context\Context;
use Drupal\Core\Plugin\Context\ContextProviderInterface;
use Drupal\Core\Plugin\Context\EntityContext;
use Drupal\Core\Plugin\Context\EntityContextDefinition;
use Drupal\Core\Routing\RouteMatchInterface;
use Drupal\node\Entity\Node;
use Drupal\Core\StringTranslation\StringTranslationTrait;

/**
 * Sets the current node as a context on node routes.
 */
class NodeRouteContext implements ContextProviderInterface {
    use StringTranslationTrait;
    
    /**
     * The route match object.
     *
     * @var \Drupal\Core\Routing\RouteMatchInterface
     */
    protected $routeMatch;
    
    /**
     * Constructs a new NodeRouteContext.
     *
     * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
     *   The route match object.
     */
    public function __construct(RouteMatchInterface $route_match) {
        $this->routeMatch = $route_match;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getRuntimeContexts(array $unqualified_context_ids) {
        $result = [];
        $context_definition = EntityContextDefinition::create('node')->setRequired(FALSE);
        $value = NULL;
        if (($route_object = $this->routeMatch
            ->getRouteObject()) && ($route_contexts = $route_object->getOption('parameters')) && isset($route_contexts['node'])) {
            if ($node = $this->routeMatch
                ->getParameter('node')) {
                $value = $node;
            }
        }
        elseif ($this->routeMatch
            ->getRouteName() == 'node.add') {
            $node_type = $this->routeMatch
                ->getParameter('node_type');
            $value = Node::create([
                'type' => $node_type->id(),
            ]);
        }
        $cacheability = new CacheableMetadata();
        $cacheability->setCacheContexts([
            'route',
        ]);
        $context = new Context($context_definition, $value);
        $context->addCacheableDependency($cacheability);
        $result['node'] = $context;
        return $result;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getAvailableContexts() {
        $context = EntityContext::fromEntityTypeId('node', $this->t('Node from URL'));
        return [
            'node' => $context,
        ];
    }

}