how to automatically choose variants based on the quantity of the main product

Hi,

It will be hard to do it like that.
I would recommend a simpler solution.
Just remove the variants and characteristics of your product, and instead, in the "quantity input method" setting of the product, select "show select".
That way, instead of an input field for the quantity next to the add to cart button, you'll have a dropdown starting from 1 and going up to the quantity of the product. So you won't have to code anything.

Hi,

If you really want to do what you're talking about, the only solution I can see is to edit the file components/com_hikashop/views/product/view.html.php and in the "show" function, after the query to load the main details of the product, dynamically generate the variants with 2 or 3 MySQL queries based on the quantity of the product.
Or even generate them all in the backend, and remove the ones you don't want once they are loaded by the MySQL query in the "show" function, it will be simpler.