protected function getVerticesAdjacent(Vertex $vertex)
{
if ($this->direction === self::DIRECTION_FORWARD) {
return $vertex->getVerticesEdgeTo();
} elseif ($this->direction === self::DIRECTION_REVERSE) {
return $vertex->getVerticesEdgeFrom();
} elseif ($this->direction === self::DIRECTION_BOTH) {
return $vertex->getVerticesEdge();
} else {
throw new DomainException('Should not happen. Invalid direction setting');
}
}