Shell Programming and Scripting

hello all
this is my frist post, i feel sorry if this is wrongly classified or a duplicate one.
issue is like i need help in vi as subject lines says
i am having a file which is comma seperated something like mentioned below

abc, xydfg, sdfiert, rsdfkh, wrtiurte , ertoue
asdsdfsdf, rtertre, ertrete, ertretre
adjfsdfs, sdfshkj
akjdhfsdf, sdfkjhhert, srterkjh

for what ever reason, i want to make this file in the following format where there should be only last 2 columns or ar most last 3.

this is what i want this file to look like

abc xydfg sdfiert rsdfkh, wrtiurte , ertoue
asdsdfsdf rtertre, ertrete, ertretre
adjfsdfs, sdfshkj
,akjdhfsdf, sdfkjhhert, srterkjh


I want this file should have only last 3 commas (,) and all other should be either deleted or replaced by space.


Kindly help

Thanks in advance

Code:

$ awk -F"," '{printf("%s,%s,%s\n",$(NF-2),$(NF-1),$NF)}' test.txt
 rsdfkh, wrtiurte , ertoue
 rtertre, ertrete, ertretre
adjfsdfs, sdfshkj,adjfsdfs, sdfshkj
akjdhfsdf, sdfkjhhert, srterkjh

$ cat test.txt
abc, xydfg, sdfiert, rsdfkh, wrtiurte , ertoue
asdsdfsdf, rtertre, ertrete, ertretre
adjfsdfs, sdfshkj
akjdhfsdf, sdfkjhhert, srterkjh