Handling defaults values for both interactive and non-interactive use

[Heime]

How is one to handle setting defaults for both interactive
and non-interactive use, properly ?

(defun xiakos-context (search-text &optional n bfrn)

  (setq n (or n 8))
  (setq bfrn (or bfrn "Context"))

  (interactive
    (list
      (read-string " Search Text: ")
      (read-number " Number of Context Lines: ")
      (read-string " Buffer Name: ")))

  (if (string-match-p "^\\s-*$" bfrn) "Context")