Google Pay Per Clicks / Analytics API

Hi, I have a website that looks up visiting IP addresses and then where possible identifies the company visiting the website. At the moment the website identifies the refering link etc. What i am looking for is somebody to build a piece of code that connects to either google analytics or PPC depending on which will provide the most accurate results and identify which visitors have been driven to the website through Pay Per click links. At present i think the only way these can be identified is through using an API, although i am open to suggestions. Because this system is used by multiple websites, the code would need to allow the user to enter their google details, which we will store in a database encrypted and then automatically login to their account and update the information in our mysql database to show which visitors were brought to the website via ppc links on a cron job. Thanks