تعديلات على موقع Modify Opencart Script

I would to like modify the Opencart journal 3 theme "Add to cart" button behavior as follows:

When the "Add to cart" button is clicked, the selected item is added to the cart and the button changes to a quantity increment selector with plus/minus buttons. (There should be no "View cart" button, either.)

The quantity in the cart can then be increased or decreased by clicking the plus/minus buttons on the quantity selector.

If the quantity is reduced down to zero, the quantity increment button reverts backs to the "Add to cart" button.

All these actions should take place without reloading the page. I would ideally like to apply this to all areas of the shop (shop archive pages, product pages, quick view modal windows, cart), however if this is not possible then just on the shop page is fine.

Please refer to the resources below for examples of the ideal finished product:

https://happyappleseddon....

https://www.woolworths.co...

Click here to see a working example on The Happy Apple's website

Click here to see a working example on Woolworths' website

Any help would be much appreciated!