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

;; Copyright (C) 1997, 2005 Free Software Foundation

;; Author: Hrvoje Niksic <hniksic@xemacs.org>
;; Keywords: minibuffer
;; Version: 7

;; 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 2, 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; see the file COPYING.  If not, write to the
;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
;; Boston, MA 02110-1301, USA.

;;; 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 Emacs is about the exit,
;; `savehist-save' will dump the contents of various minibuffer
;; histories (as determined by `savehist-history-variables') to a save
;; file (`~/.emacs-history' by default).  Although the package was
;; designed for saving the minibuffer histories, any variables can be
;; saved that way.

;; To use savehist, put the following to `~/.emacs':
;;
;; (require 'savehist)
;; (savehist-load)

;; Be sure to have `savehist.el' in a directory that is in your
;; load-path, and byte-compile it.

;;; Code:

(require 'custom)

;; User variables

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

(defcustom savehist-history-variables
  '(
    ;; Catch-all minibuffer history
    minibuffer-history
    ;; File-oriented commands
    file-name-history
    ;; Regexp-related reads
    regexp-history
    ;; Searches in minibuffer (via `M-r' and such)
    minibuffer-history-search-history
    ;; Query replace
    query-replace-history
    ;; eval-expression (`M-:')
    read-expression-history
    ;; shell-command (`M-!')
    shell-command-history
    ;; compile
    compile-history
    ;; find-tag (`M-.')
    find-tag-history
    ;; grep
    grep-history
    ;; Viper stuff
    vip-ex-history vip-search-history
    vip-replace1-history vip-replace2-history
    vip-shell-history vip-search-history

    ;; XEmacs-specific:
    ;; Buffer-related commands
    buffer-history
    ;; Reads of variables and functions
    variable-history function-history
    ;; Extended commands
    read-command-history

    ;; Info, lookup, and bookmark historys
    Info-minibuffer-history
    Info-search-history
    Manual-page-minibuffer-history

    ;; Emacs-specific:
    ;; Extended commands
    extended-command-history)
  "*List of symbols to be saved.
Every symbol should refer to a variable.  The variable will be saved
only if it is bound and has a non-nil value.  Thus it is safe to
specify a superset of the variables a user is expected to want to
save.

Default value contains minibuffer history variables used by Emacs, XEmacs,
and Viper (uh-oh).  Note that, if you customize this variable, you
can lose the benefit of future versions of Emacs adding new values to
the list.  Because of that it might be more useful to add values using
`add-to-list'."
  :type '(repeat (symbol :tag "Variable"))
  :group 'savehist)

(defcustom savehist-file "~/.emacs-history"
  "*File name to save minibuffer history to.
The minibuffer history is a series of Lisp expressions, which should be
loaded using `savehist-load' from your .emacs.  See `savehist-load' for
more details."
  :type 'file
  :group 'savehist)

(defcustom savehist-length 100
  "*Maximum length of a minibuffer list.
If set to nil, the length is unlimited."
  :type '(choice integer
		 (const :tag "Unlimited" nil))
  :group 'savehist)

(defcustom savehist-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 during which savehist should autosave the history buffer."
  :type 'integer
  :group 'savehist)

(defvar savehist-coding-system
  ;; UTF-8 is usually preferable to ISO-2022-8 when available, but under
  ;; XEmacs, UTF-8 is provided by external packages, and may not always be
  ;; available, so even if it currently is available, we prefer not to
  ;; use is.
  (if (featurep 'xemacs) 'iso-2022-8 'utf-8)
  "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)

(defconst savehist-no-conversion (if (featurep 'xemacs) 'binary 'no-conversion)
  ;; FIXME: Why not use savehist-coding-system?
  "Coding system without conversion, only used for calculating checksums.")

;; Functions

;;;###autoload
(defun savehist-load (&optional no-hook)
  "Load the minibuffer histories from `savehist-file'.
Unless NO-HOOK is specified, the function will also add the save function
to `kill-emacs-hook' and on a timer, ensuring that the minibuffer contents
will be saved before leaving Emacs.

This function should be normally used from your Emacs init file.  Since it
removes your current minibuffer histories, it is unwise to call it at any
other time."
  (interactive "P")
  (unless no-hook
    (add-hook 'kill-emacs-hook 'savehist-autosave)
    ;; Install an invocation of savehist-autosave on a timer.  This
    ;; should not cause a noticeable delay -- savehist-autosave
    ;; executes in under 5 ms on my system.
    (unless savehist-timer
      (setq savehist-timer
	    (if (featurep 'xemacs)
		(start-itimer
		 "savehist" 'savehist-autosave savehist-autosave-interval
		 savehist-autosave-interval)
	      (run-with-idle-timer savehist-autosave-interval savehist-autosave-interval
                                   'savehist-autosave)))))
  ;; Don't set coding-system-for-read here.  We rely on autodetection
  ;; and 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 t (not (interactive-p))))

;;;###autoload
(defun savehist-save (&optional auto-save)
  "Save the histories from `savehist-history-variables' to `savehist-file'.
Unbound symbols referenced in `savehist-history-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")
    (let ((print-length nil)
	  (print-string-length nil)
	  (print-level nil)
	  (print-readably t)
	  (print-quoted t))
      (dolist (sym savehist-history-variables)
	(when (boundp sym)
	  (let ((value (savehist-process-for-saving (symbol-value sym))))
	    (prin1 `(setq ,sym ',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.)
	(let ((file-precious-flag t)
	      (coding-system-for-write savehist-coding-system))
	  (write-region (point-min) (point-max) savehist-file nil
			(unless (interactive-p) 'quiet)))
	(when savehist-modes
	  (set-file-modes savehist-file savehist-modes))
	(setq savehist-last-checksum checksum)))))

(defun savehist-autosave ()
  "Save the minibuffer history if it has been modified since the last save."
  (savehist-save t))

(defun savehist-process-for-saving (value)
  ;; Process VALUE for saving to file.  If it is a list, retain only
  ;; the first `savehist-length' values and prune non-printable ones.
  ;; If VALUE is not a list, return it as-is if it is printable and
  ;; nil otherwise.
  (cond
   ((listp value)
    (when (and savehist-length (> (length value) savehist-length))
      ;; This should be: (setq value (subseq value 0 savehist-length))
      (setq value (copy-sequence value))
      (setcdr (nthcdr savehist-length value) nil))
    ;; And this should be (remove-if-not #'savehist-printable value)
    (delq nil (mapcar (lambda (x) (if (savehist-printable x) x)) value)))
   ((savehist-printable value) value)
   (t nil)))

(defun savehist-printable (value)
  "Return non-nil if VALUE is printable."
  ;; Quick response for oft-encountered types known to be printable.
  (cond
   ((stringp value))
   ((numberp value))
   ((symbolp value))
   (t
    ;; For others, check explicitly.
    (condition-case nil
	(let ((print-readably t)
	      (print-level nil)
	      (chars ()))
	  ;; Print the value into a string...
	  (prin1 value (lambda (char) (push char chars)))
	  ;; ...and attempt to read it.
	  (read (apply #'string (nreverse chars)))
	  ;; The attempt worked: the object is printable.
	  t)
      ;; The attempt failed: the object is not printable.
      (error nil)))))

(provide 'savehist)

;; arch-tag: b3ce47f4-c5ad-4ebc-ad02-73aba705cf9f
;;; savehist.el ends here