getting replica identity fields for table

Question

I’m using Postgres, and I want to know all the replica identity fields of table

Meaning -

I can get the replica identity type by

  SELECT CASE relreplident

     WHEN 'd' THEN 'default'
     WHEN 'n' THEN 'nothing'
     WHEN 'f' THEN 'full'
     WHEN 'i' THEN 'index'
     END AS replica_identity
     FROM pg_class

     WHERE oid = 'mytablename'::regclass;`



and then -


if the replica identity is FULL - I want all the columns


if the replica identity is DEFAULT - I want the pk’s for the table


if the replica identity is INDEX - I want to get the columns defined for the specific index used for the replica identity


if the replica identity is NOTHING - empty list I guess…



Is there a simple way to get this? Is it stored somewhere?
or should I just create the 4 “ifs” I wrote above and in each case do different query?

I can do this by actually writing the code I did as pseudo code, but looking maybe for simpler option