;;; savehist.el --- Save minibuffer history

;; Copyright (C) 1997, 2005-2014 Free Software Foundation, Inc.

;; Author: Hrvoje Niksic <hniksic@xemacs.org>
;; Maintainer: emacs-devel@gnu.org
;; Keywords: minibuffer
;; Version: 24

;; This file is part of GNU Emacs.

;; GNU Emacs 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 Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; Many editors (e.g. Vim) have the feature of saving minibuffer
;; history to an external file after exit.  This package provides the
;; same feature in Emacs.  When set up, it saves recorded minibuffer
;; histories to a file (`~/.emacs-history' by default).  Additional
;; variables may be specified by customizing
;; `savehist-additional-variables'.

;; To use savehist, turn on savehist-mode by putting the following in
;; `~/.emacs':
;;
;;     (savehist-mode 1)
;;
;; or with customize: `M-x customize-option RET savehist-mode RET'.
;;
;; You can also explicitly save history with `M-x savehist-save' and
;; load it by loading the `savehist-file' with `M-x load-file'.

;; If you are using a version of Emacs that does not ship with this
;; package, be sure to have `savehist.el' in a directory that is in
;; your load-path, and to byte-compile it.

;;; Code:

(require 'custom)
(eval-when-compile
  (if (featurep 'xemacs) (require 'cl)))

;; User variables

(defgroup savehist nil
  "Save minibuffer history."
  :version "22.1"
  :group 'minibuffer)

(defcustom savehist-save-minibuffer-history t
  "If non-nil, save all recorded minibuffer histories.
If you want to save only specific histories, use `savehist-save-hook'
to modify the value of `savehist-minibuffer-history-variables'."
  :type 'boolean
  :group 'savehist)

(defcustom savehist-additional-variables ()
  "List of additional variables to save.
Each element is a symbol whose value will be persisted across Emacs
sessions that use Savehist.  The contents of variables should be
printable with the Lisp printer.  You don't need to add minibuffer
history variables to this list, all minibuffer histories will be
saved automatically as long as `savehist-save-minibuffer-history' is
non-nil.

User options should be saved with the Customize interface.  This
list is useful for saving automatically updated variables that are not
minibuffer histories, such as `compile-command' or `kill-ring'."
  :type '(repeat variable)
  :group 'savehist)

(defcustom savehist-ignored-variables nil ;; '(command-history)
  "List of additional variables not to save."
  :type '(repeat variable)
  :group 'savehist)

(defcustom savehist-file
  (locate-user-emacs-file "history" ".emacs-history")
  "File name where minibuffer history is saved to and loaded from.
The minibuffer history is a series of Lisp expressions loaded
automatically when Savehist mode is turned on.  See `savehist-mode'
for more details.

If you want your minibuffer history shared between Emacs and XEmacs,
customize this value and make sure that `savehist-coding-system' is
set to a coding system that exists in both emacsen."
  :type 'file
  :group 'savehist)

(defcustom savehist-file-modes #o600
  "Default permissions of the history file.
This is decimal, not octal.  The default is 384 (0600 in octal).
Set to nil to use the default permissions that Emacs uses, typically
mandated by umask.  The default is a bit more restrictive to protect
the user's privacy."
  :type 'integer
  :group 'savehist)

(defcustom savehist-autosave-interval (* 5 60)
  "The interval between autosaves of minibuffer history.
If set to nil, disables timer-based autosaving."
  :type '(choice (const :tag "Disabled" nil)
                 (integer :tag "Seconds"))
  :group 'savehist)

(defcustom savehist-mode-hook nil
  "Hook called when Savehist mode is turned on."
  :type 'hook
  :group 'savehist)

(defcustom savehist-save-hook nil
  "Hook called by `savehist-save' before saving the variables.
You can use this hook to influence choice and content of variables
to save."
  :type 'hook
  :group 'savehist)

;; This should be capable of representing characters used by Emacs.
;; We prefer UTF-8 over ISO 2022 because it is well-known outside
;; Mule.  XEmacs prior to 21.5 had UTF-8 provided by an external
;; package which may not be loaded, which is why we check for version.
(defvar savehist-coding-system (if (and (featurep 'xemacs)
					(<= emacs-major-version 21)
					(< emacs-minor-version 5))
				   'iso-2022-8 'utf-8-unix)
  "The coding system Savehist uses for saving the minibuffer history.
Changing this value while Emacs is running is supported, but considered
unwise, unless you know what you are doing.")

;; Internal variables.

(defvar savehist-timer nil)

(defvar savehist-last-checksum nil)

(defvar savehist-minibuffer-history-variables nil
  "List of minibuffer histories.
The contents of this variable is built while Emacs is running, and saved
along with minibuffer history.  You can change its value off
`savehist-save-hook' to influence which variables are saved.")

(defconst savehist-no-conversion (if (featurep 'xemacs) 'binary 'no-conversion)
  "Coding system without any conversion.
This is used for calculating an internal checksum.  Should be as fast
as possible, ideally simply exposing the internal representation of
buffer text.")

(defvar savehist-loaded nil
  "Whether the history has already been loaded.
This prevents toggling Savehist mode from destroying existing
minibuffer history.")

(when (featurep 'xemacs)
  ;; Must declare this under XEmacs, which doesn't have built-in
  ;; minibuffer history truncation.
  (defvar history-length 100))

;; Functions.

;;;###autoload
(define-minor-mode savehist-mode
  "Toggle saving of minibuffer history (Savehist mode).
With a prefix argument ARG, enable Savehist mode if ARG is
positive, and disable it otherwise.  If called from Lisp, enable
the mode if ARG is omitted or nil.

When Savehist mode is enabled, minibuffer history is saved
periodically and when exiting Emacs.  When Savehist mode is
enabled for the first time in an Emacs session, it loads the
previous minibuffer history from `savehist-file'.

This mode should normally be turned on from your Emacs init file.
Calling it at any other time replaces your current minibuffer
histories, which is probably undesirable."
  :global t
  (if (not savehist-mode)
      (savehist-uninstall)
    (when (and (not savehist-loaded)
	       (file-exists-p savehist-file))
      (condition-case errvar
	  (progn
	    ;; Don't set coding-system-for-read -- we rely on the
	    ;; coding cookie to convey that information.  That way, if
	    ;; the user changes the value of savehist-coding-system,
	    ;; we can still correctly load the old file.
	    (load savehist-file nil (not (called-interactively-p 'interactive)))
	    (setq savehist-loaded t))
	(error
	 ;; Don't install the mode if reading failed.  Doing so would
	 ;; effectively destroy the user's data at the next save.
	 (setq savehist-mode nil)
	 (savehist-uninstall)
	 (signal (car errvar) (cdr errvar)))))
    (savehist-install)))

(defun savehist-load ()
  "Load the variables stored in `savehist-file' and turn on Savehist mode.
If `savehist-file' is in the old format that doesn't record
the value of `savehist-minibuffer-history-variables', that
value is deducted from the contents of the file."
  (declare (obsolete savehist-mode "22.1"))
  (savehist-mode 1)
  ;; Old versions of savehist distributed with XEmacs didn't save
  ;; savehist-minibuffer-history-variables.  If that variable is nil
  ;; after loading the file, try to intuit the intended value.
  (when (null savehist-minibuffer-history-variables)
    (setq savehist-minibuffer-history-variables
          (with-temp-buffer
	    (ignore-errors
	      (insert-file-contents savehist-file))
            (let ((vars ()) form)
              (while (setq form (condition-case nil
				    (read (current-buffer)) (error nil)))
		;; Each form read is of the form (setq VAR VALUE).
		;; Collect VAR, i.e. (nth form 1).
                (push (nth 1 form) vars))
              vars)))))

(defun savehist-install ()
  "Hook Savehist into Emacs.
Normally invoked by calling `savehist-mode' to set the minor mode.
Installs `savehist-autosave' in `kill-emacs-hook' and on a timer.
To undo this, call `savehist-uninstall'."
  (add-hook 'minibuffer-setup-hook 'savehist-minibuffer-hook)
  (add-hook 'kill-emacs-hook 'savehist-autosave)
  ;; Install an invocation of savehist-autosave on a timer.  This
  ;; should not cause noticeable delays for users -- savehist-autosave
  ;; executes in under 5 ms on my system.
  (when (and savehist-autosave-interval
	     (null savehist-timer))
    (setq savehist-timer
	  (if (featurep 'xemacs)
	      (start-itimer
	       "savehist" 'savehist-autosave savehist-autosave-interval
	       savehist-autosave-interval)
	    (run-with-timer savehist-autosave-interval
			    savehist-autosave-interval 'savehist-autosave)))))

(defun savehist-uninstall ()
  "Undo installing savehist.
Normally invoked by calling `savehist-mode' to unset the minor mode."
  (remove-hook 'minibuffer-setup-hook 'savehist-minibuffer-hook)
  (remove-hook 'kill-emacs-hook 'savehist-autosave)
  (when savehist-timer
    (if (featurep 'xemacs)
	(delete-itimer savehist-timer)
      (cancel-timer savehist-timer))
    (setq savehist-timer nil)))

;; From XEmacs?
(defvar print-readably)
(defvar print-string-length)

(defun savehist-save (&optional auto-save)
  "Save the values of minibuffer history variables.
Unbound symbols referenced in `savehist-additional-variables' are ignored.
If AUTO-SAVE is non-nil, compare the saved contents to the one last saved,
 and don't save the buffer if they are the same."
  (interactive)
  (with-temp-buffer
    (insert
     (format ";; -*- mode: emacs-lisp; coding: %s -*-\n" savehist-coding-system)
     ";; Minibuffer history file, automatically generated by `savehist'.\n\n")
    (run-hooks 'savehist-save-hook)
    (let ((print-length nil)
	  (print-string-length nil)
	  (print-level nil)
	  (print-readably t)
	  (print-quoted t))
      ;; Save the minibuffer histories, along with the value of
      ;; savehist-minibuffer-history-variables itself.
      (when savehist-save-minibuffer-history
	(prin1 `(setq savehist-minibuffer-history-variables
		      ',savehist-minibuffer-history-variables)
	       (current-buffer))
	(insert ?\n)
	(dolist (symbol savehist-minibuffer-history-variables)
	  (when (and (boundp symbol)
		     (not (memq symbol savehist-ignored-variables)))
	    (let ((value (savehist-trim-history (symbol-value symbol)))
		  excess-space)
	      (when value		; Don't save empty histories.
		(insert "(setq ")
		(prin1 symbol (current-buffer))
		(insert " '(")
		;; We will print an extra space before the first element.
		;; Record where that is.
		(setq excess-space (point))
		;; Print elements of VALUE one by one, carefully.
		(dolist (elt value)
		  (let ((start (point)))
		    (insert " ")
		    ;; Try to print and then to read an element.
		    (condition-case nil
			(progn
			  (prin1 elt (current-buffer))
			  (save-excursion
			    (goto-char start)
			    (read (current-buffer))))
		      (error
		       ;; If writing or reading gave an error, comment it out.
		       (goto-char start)
		       (insert "\n")
		       (while (not (eobp))
			 (insert ";;; ")
			 (forward-line 1))
		       (insert "\n")))
		    (goto-char (point-max))))
		;; Delete the extra space before the first element.
		(save-excursion
		  (goto-char excess-space)
		  (if (eq (following-char) ?\s)
		      (delete-region (point) (1+ (point)))))
		(insert "))\n"))))))
      ;; Save the additional variables.
      (dolist (symbol savehist-additional-variables)
	(when (boundp symbol)
	  (let ((value (symbol-value symbol)))
	    (when (savehist-printable value)
	      (prin1 `(setq ,symbol ',value) (current-buffer))
	      (insert ?\n))))))
    ;; If autosaving, avoid writing if nothing has changed since the
    ;; last write.
    (let ((checksum (md5 (current-buffer) nil nil savehist-no-conversion)))
      (unless (and auto-save (equal checksum savehist-last-checksum))
	;; Set file-precious-flag when saving the buffer because we
	;; don't want a half-finished write ruining the entire
	;; history.  Remember that this is run from a timer and from
	;; kill-emacs-hook, and also that multiple Emacs instances
	;; could write to this file at once.
	(let ((file-precious-flag t)
	      (coding-system-for-write savehist-coding-system))
	  (write-region (point-min) (point-max) savehist-file nil
			(unless (called-interactively-p 'interactive) 'quiet)))
	(when savehist-file-modes
	  (set-file-modes savehist-file savehist-file-modes))
	(setq savehist-last-checksum checksum)))))

(defun savehist-autosave ()
  "Save the minibuffer history if it has been modified since the last save.
Does nothing if Savehist mode is off."
  (when savehist-mode
    (savehist-save t)))

(defun savehist-trim-history (value)
  "Retain only the first `history-length' items in VALUE.
Only used under XEmacs, which doesn't (yet) implement automatic
trimming of history lists to `history-length' items."
  (if (and (featurep 'xemacs)
	   (natnump history-length)
	   (> (length value) history-length))
      ;; Equivalent to `(subseq value 0 history-length)', but doesn't
      ;; need cl-extra at run-time.
      (loop repeat history-length collect (pop value))
    value))

(defun savehist-printable (value)
  "Return non-nil if VALUE is printable."
  (cond
   ;; Quick response for oft-encountered types known to be printable.
   ((numberp value))
   ((symbolp value))
   ;; String without properties
   ((and (stringp value)
	 (equal-including-properties value (substring-no-properties value))))
   (t
    ;; For others, check explicitly.
    (with-temp-buffer
      (condition-case nil
	  (let ((print-readably t) (print-level nil))
	  ;; Print the value into a buffer...
	  (prin1 value (current-buffer))
	  ;; ...and attempt to read it.
	  (read (point-min-marker))
	  ;; The attempt worked: the object is printable.
	  t)
	;; The attempt failed: the object is not printable.
	(error nil))))))

(defun savehist-minibuffer-hook ()
  (unless (or (eq minibuffer-history-variable t)
	      ;; XEmacs sets minibuffer-history-variable to t to mean "no
	      ;; history is being recorded".
	      (memq minibuffer-history-variable savehist-ignored-variables))
    (add-to-list 'savehist-minibuffer-history-variables
		 minibuffer-history-variable)))

(provide 'savehist)


;;; savehist.el ends here