How can I set up gift coupons on my ecommerce site?

[rajivmadan7]

I want to implement the followings:

1. The Top menu would have "gift coupons" option

2. Once you click on that , it will show various options   a) INR 250  b) INR 500 , c) INR 1000 etc

3. once you select any option and BUY it , a unique discount code would be generated  which would be stored at the backend

4. User can apply the code during checkout process and suitable amount would be deducted from the original price