make a simple pie chart directive with d3js

make a simple pie chart directive with d3js

I am trying to make a simple pie chart directive with d3js and angular.js
based on this example
The datas are loaded with $resource. The datas are available inside the
directive as a json object named 'values', but i don't know how to use
them with d3.
i tried
json = JSON.parse( values );
but it doesn't work.
here is the whole code: http://plnkr.co/edit/XDyWlLY5R1ZZ4sKn5n3v?p=preview