Appointments+ - Ajax data download

Hello Sir,

I'd like to ask about linking appointments+ with ajax. I'd like to have a service-select box and after selecting proper service i'd like to display a box with service providers autoloaded - like on the video you added. However I can't find any ready script to do this so here's my question. Do I have to create separate php file to query from javascript & download proper service providers according to a service? How may i match it?

A link to plugin documentation would be nice.