Webmaster expert with solid server experience

Hi I need someone to write a code or tool for us to limit visitors to our website. This code will only allow certain users which comes from certain domain. For ex: If the user comes from google search results ------> Show the website If user comes from the tool bar search or any other directory ----------> show maintenance page or dummy site If any one who has idea about this kind of solution please bid and write a short information about the solution. Anyone who send a generic bid text will be rejected immediately