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(defvar backup-before-save-directory (file-name-concat user-emacs-directory "backups"))
(unless (file-exists-p backup-before-save-directory)
(mkdir backup-before-save-directory))
(defun backup-before-save-format-path (path number)
(format "%s.~%s~" path number))
(defun backup-before-save-extension (path)
(let* ((i (string-search "." (reverse path)))
(extension (substring path (- (length path) i))))
extension))
(defun backup-before-save-no-extension (path)
(let* ((i (string-search "." (reverse path)))
(no-extension (substring path 0 (- (length path) (+ i 1)))))
no-extension))
(defun backup-before-save-number (path)
(let* ((extension (backup-before-save-extension path))
(extracted (substring extension 1 (- (length extension) 1)))
(as-number (unless (zerop (length extracted))
(string-to-number extracted))))
as-number))
(defun backup-before-save-shift-path (path)
(let* ((without-extension (backup-before-save-no-extension path))
(number (backup-before-save-number path))
(next-number (+ number 1))
(shifted-path (backup-before-save-format-path
without-extension
next-number)))
shifted-path))
(defun backup-before-save-shift-backup (path)
(let ((next-path (backup-before-save-shift-path path)))
(when (file-exists-p next-path)
(backup-before-save-shift-backup next-path))
(rename-file path next-path)))
(defun backup-before-save-function ()
(unless backup-inhibited
(let* ((full-path (buffer-file-name))
(base-path (file-name-nondirectory full-path))
(backup-full-path (file-name-concat backup-before-save-directory base-path))
(backup-full-path-numbered (backup-before-save-format-path backup-full-path 0)))
(when (file-exists-p full-path)
(when (file-exists-p backup-full-path-numbered)
(backup-before-save-shift-backup backup-full-path-numbered))
(copy-file full-path backup-full-path-numbered)))))
(add-hook 'before-save-hook 'backup-before-save-function)
(provide 'backup-before-save)
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