(defun wrap-or-unwrap-region (start end &optional arg)
  "Without prefix arg: unfill region.
With prefix arg: fill region."
  (interactive "rP")
  (save-excursion
    (if arg
        (fill-region start end)
      (let ((temp-fill-column fill-column))
        (setq fill-column 10000)        ; TODO: find a better value
        (fill-region start end)
        (setq fill-column temp-fill-column)))))

(defun wrap-or-unwrap-buffer (&optional arg)
  "Without prefix arg: unfill buffer.
With prefix arg: fill buffer."
  (interactive "P")
  (wrap-or-unwrap-region (point-min) (point-max) arg))