public function getDistance(int $point1 = null, int $point2 = null)
{
    if (! $this->existsPoints($point1, $point2)) {
        throw new UnknownPointsSpecifiedException();
    }

    return $this->getSquareForPoints($point1, $point2);
}

protected function getSquareForPoints(int $point1, int $point2): float
{
    $p1 = $this->points[$point1];
    $p2 = $this->points[$point2];

    return sqrt((float) (
        pow(($p2[0] - $p1[0]), 2) +
        pow(($p2[1] - $p1[1]), 2)
    ));
}

protected function existsPoints(int $point1 = null, int $point2 = null): bool
{
  return isset($this->points[$point1]) && isset($this->points[$point2]);
}