class EntityRouteEnhancer

class EntityRouteEnhancer implements EnhancerInterface {
    
    /**
     * {@inheritdoc}
     */
    public function enhance(array $defaults, Request $request) {
        $route = $defaults[RouteObjectInterface::ROUTE_OBJECT];
        if (!$this->applies($route)) {
            return $defaults;
        }
        if (empty($defaults['_controller'])) {
            if (!empty($defaults['_entity_form'])) {
                $defaults = $this->enhanceEntityForm($defaults, $request);
            }
            elseif (!empty($defaults['_entity_list'])) {
                $defaults = $this->enhanceEntityList($defaults, $request);
            }
            elseif (!empty($defaults['_entity_view'])) {
                $defaults = $this->enhanceEntityView($defaults, $request);
            }
        }
        return $defaults;
    }
    
    /**
     * Returns whether the enhancer runs on the current route.
     *
     * @param \Symfony\Component\Routing\Route $route
     *   The current route.
     *
     * @return bool
     */
    protected function applies(Route $route) {
        return !$route->hasDefault('_controller') && ($route->hasDefault('_entity_form') || $route->hasDefault('_entity_list') || $route->hasDefault('_entity_view'));
    }
    
    /**
     * Update defaults for entity forms.
     *
     * @param array $defaults
     *   The defaults to modify.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The Request instance.
     *
     * @return array
     *   The modified defaults.
     */
    protected function enhanceEntityForm(array $defaults, Request $request) {
        $defaults['_controller'] = 'controller.entity_form:getContentResult';
        return $defaults;
    }
    
    /**
     * Update defaults for an entity list.
     *
     * @param array $defaults
     *   The defaults to modify.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The Request instance.
     *
     * @return array
     *   The modified defaults.
     */
    protected function enhanceEntityList(array $defaults, Request $request) {
        $defaults['_controller'] = '\\Drupal\\Core\\Entity\\Controller\\EntityListController::listing';
        $defaults['entity_type'] = $defaults['_entity_list'];
        unset($defaults['_entity_list']);
        return $defaults;
    }
    
    /**
     * Update defaults for an entity view.
     *
     * @param array $defaults
     *   The defaults to modify.
     * @param \Symfony\Component\HttpFoundation\Request $request
     *   The Request instance.
     *
     * @return array
     *   The modified defaults.
     *
     * @throws \RuntimeException
     *   Thrown when an entity of a type cannot be found in a route.
     */
    protected function enhanceEntityView(array $defaults, Request $request) {
        $defaults['_controller'] = '\\Drupal\\Core\\Entity\\Controller\\EntityViewController::view';
        if (strpos($defaults['_entity_view'], '.') !== FALSE) {
            // The _entity_view entry is of the form entity_type.view_mode.
            [
                $entity_type,
                $view_mode,
            ] = explode('.', $defaults['_entity_view']);
            $defaults['view_mode'] = $view_mode;
        }
        else {
            // Only the entity type is nominated, the view mode will use the
            // default.
            $entity_type = $defaults['_entity_view'];
        }
        // Set by reference so that we get the upcast value.
        if (!empty($defaults[$entity_type])) {
            $defaults['_entity'] =& $defaults[$entity_type];
        }
        else {
            // The entity is not keyed by its entity_type. Attempt to find it
            // using a converter.
            $route = $defaults[RouteObjectInterface::ROUTE_OBJECT];
            if ($route && is_object($route)) {
                $options = $route->getOptions();
                if (isset($options['parameters'])) {
                    foreach ($options['parameters'] as $name => $details) {
                        if (!empty($details['type'])) {
                            $type = $details['type'];
                            // Type is of the form entity:{entity_type}.
                            $parameter_entity_type = substr($type, strlen('entity:'));
                            if ($entity_type == $parameter_entity_type) {
                                // We have the matching entity type. Set the '_entity' key
                                // to point to this named placeholder. The entity in this
                                // position is the one being rendered.
                                $defaults['_entity'] =& $defaults[$name];
                            }
                        }
                    }
                }
                else {
                    throw new \RuntimeException(sprintf('Failed to find entity of type %s in route named %s', $entity_type, $defaults[RouteObjectInterface::ROUTE_NAME]));
                }
            }
            else {
                throw new \RuntimeException(sprintf('Failed to find entity of type %s in route named %s', $entity_type, $defaults[RouteObjectInterface::ROUTE_NAME]));
            }
        }
        unset($defaults['_entity_view']);
        return $defaults;
    }

}