paypal and ccavenue buy button with automatic return page

I need a paypal and ccavenue buy button and I need it to go back to a return page. \You must build the return pages which will track the following - payment amount - successful payment or not? - payment id You can also track additional details if you have a pre-made script. I will add this to a database so it must be easily commented and I must be able to clearly see the variables so I can make a mysqli query to place them in db. Also let me know how to do the return automatically so the user doesn't have to click a link after payment. I need all this to go through as soon as payment is made even if they don't come back to site. It is very important that I can edit this file so please make it commented with the sections which tracks everything and the section where I can add in functions to be executed every everything is correct.