Custom Visual ShapeMapSelector

[easybaker]

So i'm making a custom visual kind of similar to Microsoft's Shape map visual and want to allow json file input in the visual formatting settings. With Microsoft's Shape map visual they allow you to add a custom map type (topojson file) that you upload.

I figured out that this corresponds to the ShapeMapSelector formattingmodel but cannot figure out how I should correlate this to the capabilities.json type so that it will allow json input. If i try to make it type: "text" or something of that sort it will just result in the formatting setting being "[object Object]" when you input a json file. Is there some type i'm missing or some way to convert the json input to text before it turns into "[object Object]"?

It would be nice to see the source code for Microsoft's Shape map visual, but all the visuals that come with powerBI aren't open source.

Thank you for any help!