SQL & PL/SQL

I need to parse out a name string which contains: first name, last name, middle name (optional) and suffix (optional). Like this:

'SMITH, JIMMY F'
'SMITH, JIMMY'
'SMITH, JIMMY FARROW'
'SMITH, JR, JIMMY F'

Possible suffix: JR, SR, II, III, IV

Here is what I have so far:

SELECT  SUBSTR('SMITH, JIMMY F', INSTR('SMITH, JIMMY F', ', ') + 1,
          INSTR('SMITH, JIMMY F',' ', 1,2)-1 - INSTR('SMITH, JIMMY F', ', ') + 1) first_name
      , SUBSTR('SMITH, JIMMY F',1,INSTR('SMITH, JIMMY F',', ')-1) last_name
      , CASE
           WHEN INSTR('SMITH, JIMMY F',' ',1,2) = 0
           THEN null
           ELSE
                 SUBSTR(TRIM(trailing '.' FROM 'SMITH, JIMMY F'),
                    INSTR(TRIM(trailing '.' FROM 'SMITH, JIMMY F'), ' ', -1) + 1)
        END middle_name
     , CASE
           WHEN INSTR('SMITH, JIMMY F','JR') > 0
           THEN
                 'JR'
           WHEN INSTR('SMITH, JIMMY F','SR') > 0
           THEN
                 'SR'
           WHEN INSTR('SMITH, JIMMY F','II') > 0
           THEN
                 'II'
           WHEN INSTR('SMITH, JIMMY F','III') > 0
           THEN
                 'III'
           WHEN INSTR('SMITH, JIMMY F','IV') > 0
           THEN
                 'IV'
           ELSE
                  null
       END  suffix
FROM dual ;

FIRST_NAME           LAST_NAME            MIDDLE_NAME  SUFFIX
-------------------- -------------------- ------------ ------
 JIMMY               SMITH                F

But I need suggestions on getting this to work with all 4 patterns listed above.