Shell script to failover the GG extract/PUMP on other server based on some checkpoints

I have a primary - Site A on which gg extract and pump running to send data to another server (on different DC - Site B - consider this as GG based standby)  where the corresponding replicat is running . Now , I need to develop a script which reverse the  gg process roles in case of any DB failover . The scripts has to automatically start the extract/pump on the Site B and replicat on Site A ( So before stopping the gg processes i need have few checkpoints like the lag, checkpoint etc...) . Could anyone share if