Build real time instant chat for buyer/seller plugin for OsClass.org script

Build real time instant chat for buyer/seller function ( plugin / add on ) for [login to view URL] script. Developer must know how to modify the OsClass Script so the real time instant chat for buyer and seller to communicate can be done ( remove / disable the contact publisher and leave your comment section area ) . include map area need to be disable. If the item listed sold there must have option for seller to mark as sold and seller and buyer can give feedback and rating each other. The real time instant chat function must be free form bugs and no delay in receive new msg or reply. In chat windows also must have function seller/buyer can upload image. ( please don't use any ready made chat function in the market its not stable and suitable ). I will be the new owner for all complete work and source code for this plugin / add on. Note: - Must have a document how to setup the plugin / add on correctly. - Make sure the chat function can be using with mobile browser ( smartphone or tablet mode ) without problem or bugs. - Must not effect with any new OsClass new version release. - The Plugin / Add on must not heavy in database and not use to much server resource Please bid if you really understand the task and can be done asap.