I need some help with php code.
I have this code in my controller/product/product.php (opencart 1.5.6):

```
            $rsNext     = $this->model_catalog_product->getProduct($product_id+1);
            $rsNext2    = $this->model_catalog_product->getProduct($product_id+2);
            $rsNext3    = $this->model_catalog_product->getProduct($product_id+3);
            $rsLast     = $this->model_catalog_product->getProduct($product_id-1);
            $rsLast2    = $this->model_catalog_product->getProduct($product_id-2);
            $rsLast3    = $this->model_catalog_product->getProduct($product_id-3);
            if($rsNext):
                $this->data['next_url'] = $this->url->link('product/product', 'product_id=' .  $rsNext['product_id']);
                $this->data['next_text']= $rsNext['name']." &gt;&gt;";

            elseif($rsNext2):
                $this->data['next_url'] = $this->url->link('product/product', 'product_id=' .  $rsNext2['product_id']);
                $this->data['next_text']= $rsNext2['name']." &gt;&gt;";

            elseif($rsNext3):
                $this->data['next_url'] = $this->url->link('product/product', 'product_id=' .  $rsNext3['product_id']);
                $this->data['next_text']= $rsNext3['name']." &gt;&gt;";
            else:
                $this->data['next_url'] = '';
                $this->data['next_text']= '';
            endif;

            if($rsLast):
                $this->data['prev_url'] = $this->url->link('product/product', 'product_id=' .  $rsLast['product_id']);
                $this->data['prev_text']= "&lt;&lt; ".$rsLast['name'];

            elseif($rsLast2):
                $this->data['prev_url'] = $this->url->link('product/product', 'product_id=' .  $rsLast2['product_id']);
                $this->data['prev_text']= "&lt;&lt; ".$rsLast2['name'];

            elseif($rsLast3):
                $this->data['prev_url'] = $this->url->link('product/product', 'product_id=' .  $rsLast3['product_id']);
                $this->data['prev_text']= "&lt;&lt; ".$rsLast3['name'];
            else:
                $this->data['prev_url'] = '';
                $this->data['prev_text']= null;
            endif;

```

How i could make this infinite, because are situations where need product\_id+15 for example or more.
Thanks!