Programmably collect data from chart

Could someone please point me in the direction to do this. Just the proper terms for what I'm trying to achive would be a wonderful start.

I'm planning to have an embedded published BI graph inside a HTML/JavaScript web page. I want the user to be able to drill down to see the data they are interested, for example, a column in a bar chart, or a segment in a pie chart etc. I then want them to right click, get a popup menu, one of options being 'colllect data'. I then must collect a list of unique identifiers for each of the items that make up that graphical element. (In a nice json structure.)

I (hopefully) can do the clicking routines and the pop menu (but if there are examples of the these - great!) but how do I identify the bar/segment the user has clicked on, and retrieve the individual IDs. (The dataset will include a unique ID for each data row.)

Many thanks

Susan