Wordpress Cookie script

Develop a simple cookie handling for our Wordpress website. Special links to our website from an affiliate will contain a querystring to the url Sample: [login to view URL] The cookie script have to write this value to a cookie with the valid time of 30 days. The cookie will be overwritten each time. On a special page we need to ask the cookie. We need the information: Is cookie available and the cookie “aid” value. We need to switch a button logik with this information.