Query formaton

In theory, yes, you can include code from a PL\SQL function directly into a query that calls a function *IF* the function can be reduced to simple SQL.  In this case however, the function includes a cursor loop and some conditional logic based on values in the last record retrieved by the cursor, so no, you certainly can't easily include this logic in a single-level query.

It may be possible to write a "max" subquery that returns just one row instead of a cursor loop, and put that inside of a "case" statement to evaluate what it returns, then put this into your query, but this is certainly not a task for a novice SQL coder!  I'm not suggesting that you are a SQL novice, but this would be a challenge for many advanced SQL developers.  Also, maintenance and/or changes of something this complex could be a problem in the future.