Magento 2 custom discount module fixing and finishing

Module is based on [login to view URL] [login to view URL] Problems: By this solution if discout amount is equal product sum with free or not free shipping payment methods is not available. If my cart amout with free shipping is zero I need Zero Subtotal Checkout, but there is no Zero Subtotal Checkout. Dont need to implement any discount logic, You can use hardcoded discount amount and result should be: Discount must be equal to product (one or sum) price, in cart total amount must be zero. Next step when I chose shipping free in payments step I must see Zero Subtotal Checkout also it must work. If I chose not free shipping in payments step I must see other payments paypal, etc. (it is so now but payment doesnt work ). Now this implementation is in UseApp\RewardPoints\Model\Total\Quote\[login to view URL] (You dont need to take into account other files like helper or adminhtml). I want additionaly 1) "Apply" and "Cancel" buttons to discount in "checkout/cart/" (You can have a look or change files UseApp\RewardPoints\view\frontend\templates\[login to view URL] , UseApp\RewardPoints\Controller\Rewardpoint\[login to view URL] but nothing is done there ) 2) If this discount is Applied cancel native discount like Promotions Cart Price Rules, and vice versa 3) Informacija apie panauduota nuolaida turi buti matoma in order. Information about used discount must be seen in the order (info, observer). Magento 2.1.11 version