Codeigniter & Authorize.net Integration

Task: Need to integrate [login to view URL] payment gateway on to the site. Our application is developed in codeIgniter. We also use a ci library “ci-merchant”. If you have a better library we are open for suggestions. Task Description: 1. Create 1 page with 3 different subscription memberships membership packages to be stored in database. 2. On user clicking buy button user should be taken to next page to enter details and credit card info. 3. You should be able to answer all my questions regard the payment gateway and help me(my coder). 4. After successful transfer a defined method should execute. 5. Similarly on failure or cancellation of the transfer it should execute a different method. All fields for above packages and user details will be provided. We already have a codeigniter developer account setup. Must work on live server not locally. Hope for a codeigniter coder experienced with [login to view URL] integration this job is too simple.