;;; delsel.el --- delete selection if you insert

;; Copyright (C) 1992, 1997-1998, 2001-2014 Free Software Foundation,
;; Inc.

;; Author: Matthieu Devin <devin@lucid.com>
;; Maintainer: emacs-devel@gnu.org
;; Created: 14 Jul 92
;; Keywords: convenience emulations

;; 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:

;; This file makes the active region be pending delete, meaning that
;; text inserted while the region is active will replace the region contents.
;; This is a popular behavior of personal computers text editors.

;; Interface:

;; Commands which will delete the selection need a 'delete-selection
;; property on their symbols; commands which insert text but don't
;; have this property won't delete the selection.  It can be one of
;; the values:
;;  'yank
;;      For commands which do a yank; ensures the region about to be
;;      deleted isn't yanked.
;;  'supersede
;;      Delete the active region and ignore the current command,
;;      i.e. the command will just delete the region.
;;  'kill
;;      `kill-region' is used on the selection, rather than
;;      `delete-region'.  (Text selected with the mouse will typically
;;      be yankable anyhow.)
;;  t
;;      The normal case: delete the active region prior to executing
;;      the command which will insert replacement text.
;;  <function>
;;      For commands which need to dynamically determine this behavior.
;;      The function should return one of the above values or nil.

;;; Code:

;;;###autoload
(defalias 'pending-delete-mode 'delete-selection-mode)

;;;###autoload
(define-minor-mode delete-selection-mode
  "Toggle Delete Selection mode.
With a prefix argument ARG, enable Delete Selection mode if ARG
is positive, and disable it otherwise.  If called from Lisp,
enable the mode if ARG is omitted or nil.

When Delete Selection mode is enabled, typed text replaces the selection
if the selection is active.  Otherwise, typed text is just inserted at
point regardless of any selection."
  :global t :group 'editing-basics
  (if (not delete-selection-mode)
      (remove-hook 'pre-command-hook 'delete-selection-pre-hook)
    (add-hook 'pre-command-hook 'delete-selection-pre-hook)))

(defun delete-active-region (&optional killp)
  "Delete the active region.
If KILLP in not-nil, the active region is killed instead of deleted."
  (if killp
      ;; Don't allow `kill-region' to change the value of `this-command'.
      (let (this-command)
	(kill-region (point) (mark) t))
    (funcall region-extract-function 'delete-only))
  t)

(defun delete-selection-helper (type)
  "Delete selection according to TYPE:
 `yank'
     For commands which do a yank; ensures the region about to be
     deleted isn't yanked.
 `supersede'
     Delete the active region and ignore the current command,
     i.e. the command will just delete the region.
 `kill'
     `kill-region' is used on the selection, rather than
     `delete-region'.  (Text selected with the mouse will typically
     be yankable anyhow.)
 t
     The normal case: delete the active region prior to executing
     the command which will insert replacement text.
 FUNCTION
     For commands which need to dynamically determine this behavior.
     FUNCTION should take no argument and return one of the above values or nil."
  (condition-case data
      (cond ((eq type 'kill)
	     (delete-active-region t)
	     (if (and overwrite-mode
		      (eq this-command 'self-insert-command))
		 (let ((overwrite-mode nil))
		   (self-insert-command
		    (prefix-numeric-value current-prefix-arg))
		   (setq this-command 'ignore))))
	    ((eq type 'yank)
	     ;; Before a yank command, make sure we don't yank the
	     ;; head of the kill-ring that really comes from the
	     ;; currently active region we are going to delete.
	     ;; That would make yank a no-op.
	     (when (and (string= (buffer-substring-no-properties
				  (point) (mark))
				 (car kill-ring))
			(fboundp 'mouse-region-match)
			(mouse-region-match))
	       (current-kill 1))
             (let ((pos (copy-marker (region-beginning))))
               (delete-active-region)
               ;; If the region was, say, rectangular, make sure we yank
               ;; from the top, to "replace".
               (goto-char pos)))
	    ((eq type 'supersede)
	     (let ((empty-region (= (point) (mark))))
	       (delete-active-region)
	       (unless empty-region
		 (setq this-command 'ignore))))
	    ((functionp type) (delete-selection-helper (funcall type)))
	    (type
	     (delete-active-region)
	     (if (and overwrite-mode
		      (eq this-command 'self-insert-command))
		 (let ((overwrite-mode nil))
		   (self-insert-command
		    (prefix-numeric-value current-prefix-arg))
		   (setq this-command 'ignore)))))
    ;; If ask-user-about-supersession-threat signals an error,
    ;; stop safe_run_hooks from clearing out pre-command-hook.
    (file-supersession (message "%s" (cadr data)) (ding))
    (text-read-only
     ;; This signal may come either from `delete-active-region' or
     ;; `self-insert-command' (when `overwrite-mode' is non-nil).
     ;; To avoid clearing out `pre-command-hook' we handle this case
     ;; by issuing a simple message.  Note, however, that we do not
     ;; handle all related problems: When read-only text ends before
     ;; the end of the region, the latter is not deleted but any
     ;; subsequent insertion will succeed.  We could avoid this case
     ;; by doing a (setq this-command 'ignore) here.  This would,
     ;; however, still not handle the case where read-only text ends
     ;; precisely where the region starts: In that case the deletion
     ;; would succeed but the subsequent insertion would fail with a
     ;; text-read-only error.  To handle that case we would have to
     ;; investigate text properties at both ends of the region and
     ;; skip the deletion when inserting text is forbidden there.
     (message "Text is read-only") (ding))))

(defun delete-selection-pre-hook ()
  "Function run before commands that delete selections are executed.
Commands which will delete the selection need a `delete-selection'
property on their symbol; commands which insert text but don't
have this property won't delete the selection.
See `delete-selection-helper'."
  (when (and delete-selection-mode (use-region-p)
	     (not buffer-read-only))
    (delete-selection-helper (and (symbolp this-command)
                                  (get this-command 'delete-selection)))))

(put 'self-insert-command 'delete-selection
     (lambda ()
       (not (run-hook-with-args-until-success
             'self-insert-uses-region-functions))))

(put 'insert-char 'delete-selection t)
(put 'quoted-insert 'delete-selection t)

(put 'yank 'delete-selection 'yank)
(put 'clipboard-yank 'delete-selection 'yank)
(put 'insert-register 'delete-selection t)
;; delete-backward-char and delete-forward-char already delete the selection by
;; default, but not delete-char.
(put 'delete-char 'delete-selection 'supersede)

(put 'reindent-then-newline-and-indent 'delete-selection t)
(put 'newline-and-indent 'delete-selection t)
(put 'newline 'delete-selection t)
(put 'electric-newline-and-maybe-indent 'delete-selection t)
(put 'open-line 'delete-selection 'kill)

;; This is very useful for canceling a selection in the minibuffer without
;; aborting the minibuffer.
(defun minibuffer-keyboard-quit ()
  "Abort recursive edit.
In Delete Selection mode, if the mark is active, just deactivate it;
then it takes a second \\[keyboard-quit] to abort the minibuffer."
  (interactive)
  (if (and delete-selection-mode (region-active-p))
      (setq deactivate-mark t)
    (abort-recursive-edit)))

(define-key minibuffer-local-map "\C-g" 'minibuffer-keyboard-quit)
(define-key minibuffer-local-ns-map "\C-g" 'minibuffer-keyboard-quit)
(define-key minibuffer-local-completion-map "\C-g" 'minibuffer-keyboard-quit)
(define-key minibuffer-local-must-match-map "\C-g" 'minibuffer-keyboard-quit)
(define-key minibuffer-local-isearch-map "\C-g" 'minibuffer-keyboard-quit)

(defun delsel-unload-function ()
  "Unload the Delete Selection library."
  (define-key minibuffer-local-map "\C-g" 'abort-recursive-edit)
  (define-key minibuffer-local-ns-map "\C-g" 'abort-recursive-edit)
  (define-key minibuffer-local-completion-map "\C-g" 'abort-recursive-edit)
  (define-key minibuffer-local-must-match-map "\C-g" 'abort-recursive-edit)
  (define-key minibuffer-local-isearch-map "\C-g" 'abort-recursive-edit)
  (dolist (sym '(self-insert-command insert-char quoted-insert yank
                 clipboard-yank insert-register newline-and-indent
                 reindent-then-newline-and-indent newline open-line))
    (put sym 'delete-selection nil))
  ;; continue standard unloading
  nil)

(provide 'delsel)

;;; delsel.el ends here