Make facebook "like" application!

Hi, I would like to promote my website by asking facebook users to "like" my facebook page and reward them a discount voucher code. One user will receive ONE code ONLY. To do that, I must have tab in my facebook page called " Confirm your prize". When user click this button -> open a form (for user to input some information we asked) -> app will check whether email of this user has received discount code or not. If not, save them in database of app. We will tick each user we want to send code and enter discount amount (%) for each user and click send. When click send, app will send code to chosen user. User then bring code to my restaurant, we will check whether this code is in our database or not. If yes, tick it as "used" so that user can not use this code again next time.