(define (die msg)
  (begin
    (write msg)
    (exit 1)))

(define (usage)
  (die "increment_version [position]\n\tposition defaults to 2"))

(define (parse-args)
  (cond
    ((eq? 0 (length zepto:args)) 2)
    ((and (string:num? (car zepto:args))
          (eq? 1 (length zepto:args)))
      (string->number (car zepto:args)))
    (else (usage))))

(define (main position)
  (if (not (file-exists? "VERSION"))
    (die "A version file is needed in the current directory")
    (let* ((version (read-contents "VERSION"))
           (new-version (|> (string:split version ".")
                            (curry map string->number)
                            list->vector
                            ($ (vector:update % position add1))
                            (curry vector:map number->string)
                            ($ (string:join % ".")))))
      (with-output-file "VERSION" (curry write new-version)))))

(main (parse-args))
(exit 0)