Zonal stats function

Hi, I'm seeing if you think this is possible. I want to create a raster function where I pass in a polygon and it returns the zonal stats average value of a value raster. I want the output raster but just the min or max of the output zone raster. I want this to function in ImageServer and I use the JS API to pass in a polygon feature set and it returns the resulting summary value. I currently have a raster function that successfully chains Rasterize Features and then Zonal Statistics functions to create the correct zone raster but not sure about the rest. Do I need a python raster function to get the output value?