$nbProducts = (int)ProductSale::getNbSales();

$category = new Category(3, $this->context->language->id);
$nbProducts = $category->getProducts(null, null, null, $this->orderBy, $this->orderWay, true);

$products = ProductSale::getBestSales($this->context->language->id, $this->p - 1, $this->n, $this->orderBy, $this->orderWay);

$products = $category->getProducts($this->context->language->id, (int)$this->p, (int)$this->n, $this->orderBy, $this->orderWay);