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;;; guix-history.el --- History of buffer information
;; Copyright © 2014 Alex Kost <alezost@gmail.com>
;; This file is part of GNU Guix.
;; GNU Guix is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.
;; GNU Guix is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; GNU General Public License for more details.
;; You should have received a copy of the GNU General Public License
;; along with this program. If not, see <http://www.gnu.org/licenses/>.
;;; Commentary:
;; This file provides support for history of buffers similar to the
;; history of a `help-mode' buffer.
;;; Code:
(require 'cl-macs)
(defvar-local guix-history-stack-item nil
"Current item of the history.
A list of the form (FUNCTION [ARGS ...]).
The item is used by calling (apply FUNCTION ARGS).")
(put 'guix-history-stack-item 'permanent-local t)
(defvar-local guix-history-back-stack nil
"Stack (list) of visited items.
Each element of the list has a form of `guix-history-stack-item'.")
(put 'guix-history-back-stack 'permanent-local t)
(defvar-local guix-history-forward-stack nil
"Stack (list) of items visited with `guix-history-back'.
Each element of the list has a form of `guix-history-stack-item'.")
(put 'guix-history-forward-stack 'permanent-local t)
(defvar guix-history-size 0
"Maximum number of items saved in history.
If 0, the history is disabled.")
(defun guix-history-add (item)
"Add ITEM to history."
(and guix-history-stack-item
(push guix-history-stack-item guix-history-back-stack))
(setq guix-history-forward-stack nil
guix-history-stack-item item)
(when (>= (length guix-history-back-stack)
(setq guix-history-back-stack
(cl-loop for elt in guix-history-back-stack
for i from 1 to guix-history-size
collect elt))))
(defun guix-history-replace (item)
"Replace current item in history with ITEM."
(setq guix-history-stack-item item))
(defun guix-history-goto (item)
"Go to the ITEM of history.
ITEM should have the form of `guix-history-stack-item'."
(or (listp item)
(error "Wrong value of history element"))
(setq guix-history-stack-item item)
(apply (car item) (cdr item)))
(defun guix-history-back ()
"Go back to the previous element of history in the current buffer."
(or guix-history-back-stack
(user-error "No previous element in history"))
(push guix-history-stack-item guix-history-forward-stack)
(guix-history-goto (pop guix-history-back-stack)))
(defun guix-history-forward ()
"Go forward to the next element of history in the current buffer."
(or guix-history-forward-stack
(user-error "No next element in history"))
(push guix-history-stack-item guix-history-back-stack)
(guix-history-goto (pop guix-history-forward-stack)))
(provide 'guix-history)
;;; guix-history.el ends here