Silverstripe visitor pattern

_config.php

<?php

Object::add_extension('SiteTree', 'ChangeDecorator');

ChangeDecorator.php

<?php

class ChangeDecorator extends DataObjectDecorator {
    
    /**
     * 
     */
    public function onAfterWrite() {
        $publisher = PublisherQueueVisitor::instance();
        $this->getOwner()->accept($publisher);
    }
    
    /**
     *
     * @param $visitor 
     */
    public function accept( $visitor ) {
        $owner = $this->getOwner();
        $methodName = "visit".get_class($owner);
        if( method_exists($visitor, $methodName)) {
            $visitor->$methodName($this->getOwner());
        }
    }
}

PublisherQueueVisitor.php

<?php

class PublisherQueueVisitor {
    
    /**
     *
     * @var array
     */
    protected $urls = array();
    
    /**
     *
     * @var PublisherQueueVisitor 
     */
    static $instance = null;
    
    /**
     *
     * @return Dispatcher 
     */
    public static function instance() {
        if( !self::$instance ) {
            self::$instance = new PublisherQueueVisitor();
        }
        return self::$instance;
    }
    
    public function visitPage(DataObject $object) {
        $this->urls[] = $object->Link();
       
    }
    
    public function visitBlogHolder(DataObject $object) {
        $this->urls[] = $object->Link();
         if( !$object->Children() ) {
            return;
        }
        foreach( $object->Children() as $children ) {
            $this->urls[] = $children->Link();
        }
    }
    
    public function visitIndexPage(DataObject $object) {
        $this->urls[] = $object->Link();
    }
    
    public function __destruct() {
        file_put_contents("/tmp/urls", var_export(array_unique($this->urls), true));
    }
}