Is it possible to get the discounted price on checkout? I want to show it on the product page

[jam_chan]

My app is creating an alternate product template. On this template, it's trying to add several items with a discount code applied using the checkout links. 

How can I get the discounted price before redirecting to checkout? I want to show this price to the customers. For example, the customer adds 3 different items ($10, $20 $30) and gets a 10% off discount. I want to show the discount total = (10 + 20 + 30) * 0.9 = $54 on the template

I don't find any ajax API possible. What is the possible way?

Store the price rule on metafield and calculate the discounted price myself? It looks quite complicated for 4 different types of discounts