PHP Messaging Script Required

I am making a site using OpenCart. Users will come and register on my site and will be buying my services. I want to give my users a system where they can chat with the customer care executives. Every User will have a chat room for every service he have purchased. So for example, if he purchases my 2 services Service A and Service B, he should see an option in his account page as "Chat Now" (I can create this in OpenCart backend). By clicking here he will be redirected to a page where he will be seen his current active services, he will select a service and will then be redirected to chat page. This page will store all the chats and will show latest 50 messages rest will be hidden by paging. This script will work exactly as the FreeLancer.com Message box. We need to show on the right side whether the customer executive is online or not, if online a grey dot should appear next to his name and if online a green dot should appear. I also need a section from where I can assign the projects to customer care executives. for every new service bought by a user, I should be able to assign the service to one executive so when he logs in he should see all his services assigned to him with the customers name and if there's any new message for him/her. What I need from you is: 1) A page where user will see his services listed and the chat page, 2) A page from where I can register the customer care executives and there login. 3) A section to assign the services to executives. I need this within 20 hours, please bid only if you can complete within this time. My budget is about 100$, I will escrow the whole payment as soon as I select a contractor and will release once work is completed. Please message me if you have any queries.