;; A disk-entry is:
;;  - a filename, or
;;  - a directory-name, or
;;  - a linkname.
;;
;; A filename is a pathname.
;; A directory-name is a pathname.
;; A linkname is a pathname.
;; A pathname is a string.

;; directory-list-fullname: pathname --> list of pathname
;; Like directory-list, except that we use build-path to return
;; a full pathname rather than just the name of the entry inside the directory.
;;
(define (directory-list-fullname f)
  (map (lambda (x) (build-path f x))
       (directory-list f)))







;; WARNING: these next functions change the disk!


;; backup-disk-entry: item --> list of string-or-false
;; 
(define (backup-disk-entry de old-suffix new-suffix)
  (cond [(file-exists? de)      (backup-file de old-suffix new-suffix)]
        [(directory-exists? de) (map (lambda (sub-de) (backup-disk-entry sub-de old-suffix new-suffix))
                                     (directory-list-fullname de))]
        [(link-exists? de)      empty]   ; A link that's not a file or dir is a dangling/circular link!
        [else (error 'backup-disk-entry "Hmmm, ~a is not a known type of disk-entry!" de)]))

        ; Note that this "map" is doing the work of calling backup-disk-entry on everything in the de.
        ; The use of "lambda" is needed only because map takes single-argument functions,
        ;    whereas backup-disk-entry needs three; the lambda provides the other two arguments.
        ;    This could also have been effected with local, rather than lambda.


;; backup-file: filename --> string or false
;;
(define (backup-file fname old-suffix new-suffix)
  (cond [(has-suffix? fname old-suffix)
         (local {(define new-fname (string-append (remove-suffix fname old-suffix) new-suffix))}
           (cond [(not (file-exists? new-fname))
                  (copy-file fname new-fname)]
                 [else false]))]
        [else false]))


(backup-disk-entry (build-path (current-directory) "comp210") ".scm" ".ss")