elisp : check vi swap file

check-vi_swp_file.el

;; if .file.swp exists :
;;   set buffer-read-only and ask to user
(defun check-vi-swp-file ()
  (let* ((fullpath (file-truename (buffer-file-name)))
         (dirpath  (file-name-directory    fullpath) )
         (fname    (file-name-nondirectory fullpath) )
         (swppath  (concat dirpath "." fname ".swp") ))
    (if (file-exists-p swppath)
        (progn
          (setq buffer-read-only 't)    ; set Read-Only.
          (if (y-or-n-p "vi swap file exists; really edit the buffer? ")
              (setq buffer-read-only 'nil) ; set Writable.
            )))))

;; (add-hook 'find-file-hooks 'check-vi-swp-file)