Add featured in sort by option on category page

Hi,

Sort by option on every category page has these options available:

• Default

• Name (A-Z)

• Name (Z-A)

• Price (high-low)

• Price (low-high)

• Model (A-Z)

• Model (Z-A)

How can I add featured option which showes featured products of that category, and date added option which shows newest added products first?

I have seen the code in category.php in catalog -> product and category.php in model-> catalog but can't understand what exactly to modify to achieve this.

Any help would be greatly appreciated.

Opencart version 2.2