How to find route of a current page?
Is there a line of code that I can use in the controller that determines the route of a current page?
For example, I would like to find the route of the page with SEO url https://example.com/desktops (this should return the route product/category).
Similarly, url such as https://example.com/index.php?route=product/product&path=18&product_id=47 should return route as product/product.
Answer
To be honest, the right answer is $this->request->get['route'];.
In order to catch the current route, you can use $this->request->get['route']; in the catalog/controller/common/header.php file in the index() function. Header.php is a part of practically any frontend output (as I understand, right now you are not sure what controller is used in http://example.com/desktops so you need right place where you can run your code in any case).
The SEO module does not unset this part of the request object. Also, keep in mind, in the middle of OpenCart code generation the $_GET array and the $this->request->get array is not the same things. You won't catch current route (in "path/controller/action" format) in $_GET superglobal php array when SEO module is in action, but you can catch it with any controller by using $this->request->get array which is prepared for you by OpenCart engine.