Code Snippet: Track referral/affiliate on a third party site using Javascript

We have an e-commerce website hosted by third party and we would like to get a developer to write a javascript for us so we can track our referrals/affiliates. The javascript may also call a php script if necessary since we hope to record this transaction with affiliate ID into mysql. We are allowed to provide javascript in the header, which is hosted in third party website. To illustrate my points, here’s the flow. 1. Customer will click on a referral link, pointing to our domain. 2. Customer will reach our landing page. We can store the referral/affiliate ID as a session or cookie here. 3. Customer will click on a search button and get redirected to a third party website. 4. Customer will select a product and make payment. 5. Customer will be directed to payment page. 6. Upon completion of payment, customer will be redirected back to a “Success” page. From this point onwards, we want to be able to track the affiliate ID who referred a successful sale on third party website, and store this transaction into our mysql. Freelancers must be willing to provide a demo if required before we award. After we award, we will create milestones and milestones will ONLY be released when we are happy with your work.