TermRouteContext.php

<?php

namespace Drupal\taxonomy\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\Core\StringTranslation\StringTranslationTrait;
use Drupal\taxonomy\Entity\Term;

/**
 * Sets the current taxonomy term as a context on taxonomy term routes.
 */
class TermRouteContext implements ContextProviderInterface {
    use StringTranslationTrait;
    
    /**
     * The route match object.
     *
     * @var \Drupal\Core\Routing\RouteMatchInterface
     */
    protected $routeMatch;
    
    /**
     * Constructs a new TermRouteContext.
     *
     * @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('taxonomy_term')->setRequired(FALSE);
        $value = NULL;
        if ($route_object = $this->routeMatch
            ->getRouteObject()) {
            $route_parameters = $route_object->getOption('parameters');
            if (isset($route_parameters['taxonomy_term']) && ($term = $this->routeMatch
                ->getParameter('taxonomy_term'))) {
                $value = $term;
            }
            elseif ($this->routeMatch
                ->getRouteName() == 'entity.taxonomy_term.add_form') {
                $vocabulary = $this->routeMatch
                    ->getParameter('taxonomy_vocabulary');
                $value = Term::create([
                    'vid' => $vocabulary->id(),
                ]);
            }
        }
        $cacheability = new CacheableMetadata();
        $cacheability->setCacheContexts([
            'route',
        ]);
        $context = new Context($context_definition, $value);
        $context->addCacheableDependency($cacheability);
        $result['taxonomy_term'] = $context;
        return $result;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getAvailableContexts() {
        $context = EntityContext::fromEntityTypeId('taxonomy_term', $this->t('Term from URL'));
        return [
            'taxonomy_term' => $context,
        ];
    }

}