public function find($index)
    {
        $result = array();
        foreach ($this->events as $event) {
            if ($index instanceof PeriodInterface && $index->containsEvent($event)) {
                $result[] = $event;
            } elseif ($index instanceof \DateTime && $event->contains($index)) {
                $result[] = $event;
            }
        }

        return $result;
    }