How to Automatically add thousand separators as number is input in EditText

Im creating a convertor application. I want to set the EditText so that when the user is inputting the number to be converted, a thousand separator (,) should be added automatically in realtime to the number once it increments by 3 figures: thousand, million, billion etc.
And when erased to below 4 figures the number goes back to normal.
Any help?