How to reuse a postgres function for triggers and generic use

Very simple question indeed. Say I have a trigger to convert some text fields coming from other tables to tsv indexes so I can implement a full text search in a performatic way.

To achieve that, I have:

• Created a function which performs my desired SQL query (works)
• Created a trigger that calls that function when my ordering.order table gets updated (works)
• Tried to reuse that same function before the trigger, because I want old data to be updated as well ( doesn't work )

migration failed: trigger functions can only be called as triggers

In short, is there any return type in a postgres function that allows me both to use it in a trigger and to be called in other places as a normal function? Thank you very much.

  CREATE OR REPLACE FUNCTION index_text_fields() RETURNS trigger AS $$
      BEGIN
         UPDATE ordering.order as uo SET tsv = setweight(to_tsvector
        (coalesce(s.name, '')), 'A')
        || setweight(to_tsvector(coalesce(split_part(o.order_ref,'-',2),'')), 'A')
        FROM ordering.order AS o  
          LEFT JOIN ordering.sender AS s  USING (order_id) 
          LEFT JOIN ordering.receiver AS r  USING (order_id)
        WHERE uo.order_id = o.order_id;
        RETURN NULL;
      END  
  $$ LANGUAGE plpgsql;

  DO $$ BEGIN
    PERFORM index_text_fields();
  END $$;


  CREATE TRIGGER orders_trigger AFTER
    INSERT OR UPDATE
      ON ordering.order FOR EACH ROW
        WHEN (pg_trigger_depth() < 1)
          EXECUTE PROCEDURE index_text_fields();