;;; double.el --- support for keyboard remapping with double clicking  -*- lexical-binding: t -*-

;; Copyright (C) 1994, 1997-1998, 2001-2023 Free Software Foundation,
;; Inc.

;; Author: Per Abrahamsen <abraham@dina.kvl.dk>
;; Keywords: i18n

;; 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 <https://www.gnu.org/licenses/>.

;;; Commentary:

;; This mode is intended for use with languages that adds a small
;; number of extra letters not available on the keyboard.
;;
;; Examples includes Scandinavian and German with an US keyboard.
;;
;; The idea is that certain keys are overloaded.  When you press it
;; once it will insert one string, and when you press it twice the
;; string will be replaced by another.  This can be used for mapping
;; keys on a US keyboard to generate characters according to the local
;; keyboard convention when pressed once, and according to US keyboard
;; convention when pressed twice.
;;
;; To use this mode, you must define the variable `double-map' and
;; then enable double mode with `M-x double-mode'.  Read the
;; documentation for both of them.
;;
;; The default mapping is for getting Danish/Norwegian keyboard layout
;; using ISO Latin 1 on a US keyboard.
;;
;; Important node: While I would like to hear comments, bug reports,
;; suggestions, please do @strong{not} expect me to put other mappings
;; than the default into this file.  There are billions and billions
;; of such mappings, and just supporting the most common would
;; increase the size of this nice small file manyfold.

;;; Code:

(defgroup double nil
  "Remap keyboard, but get original by typing the same key twice."
  :group 'i18n)

(defcustom double-map
  '((?\; "\346" ";")
    (?\' "\370" "'")
    (?\[ "\345" "[")
    (?\: "\306" ":")
    (?\" "\330" "\"")
    (?\{ "\305" "{"))
  "Alist of key translations activated by double mode.

Each entry is a list with three elements:
1. The key activating the translation.
2. The string to be inserted when the key is pressed once.
3. The string to be inserted when the key is pressed twice."
  :type '(repeat (list (character :tag "Key")
		       (string :tag "Once")
		       (string :tag "Twice"))))

(defcustom double-prefix-only t
  "Non-nil means that Double mode mapping only works for prefix keys.
That is, for any key `X' in `double-map', `X' alone will be mapped
but not `C-u X' or `ESC X' since the X is not the prefix key."
  :type 'boolean)

;;; Read Event

(defvar double-last-event nil)
;; The last key that generated a double key event.

(defun double-read-event (prompt)
  ;; Read an event
  (if isearch-mode (isearch-update))
  (if prompt
      (prog2 (message "%s%c" prompt double-last-event)
	  (read-event)
	(message ""))
    (read-event)))

(global-set-key [ignore] 'ignore)

(require 'isearch)

(define-key isearch-mode-map [ignore]
  (lambda () (interactive) (isearch-update)))

(defun double-translate-key (prompt)
  ;; Translate input events using double map.
  (let ((key last-input-event))
    (cond (unread-command-events
	   ;; Artificial event, ignore it.
	   (vector key))
	  ((and double-prefix-only
		(> (length (this-command-keys)) 1))
	   ;; This is not a prefix key, ignore it.
	   (vector key))
	  ((eq key 'magic-start)
	   ;; End of generated event.  See if he will repeat it...
	   (let ((new (double-read-event prompt))
		 (entry (assoc double-last-event double-map)))
	     (force-window-update (selected-window))
	     (if (eq new double-last-event)
		 (progn
		   (setq unread-command-events
			 (append (make-list (1- (length (nth 1 entry)))
					    127)
				 (nth 2 entry)
				 '(magic-end)
                                 unread-command-events))
		   (vector 127))
	       (push new unread-command-events)
	       [ignore])))
	  ((eq key 'magic-end)
	   ;; End of double event.  Ignore.
	   [ignore])
	  (t
	   ;; New key.
	   (let ((exp (nth 1 (assoc key double-map))))
	     (setq double-last-event key)
	     (setq unread-command-events
		   (append (substring exp 1) '(magic-start)
                           unread-command-events))
	     (vector (aref exp 0)))))))

;;; Mode

;;;###autoload
(define-minor-mode double-mode
  "Toggle special insertion on double keypresses (Double mode).

When Double mode is enabled, some keys will insert different
strings when pressed twice.  See `double-map' for details."
  :lighter " Double"
  :link '(emacs-commentary-link "double")
  (kill-local-variable 'key-translation-map)
  (when double-mode
    ;; Set up key-translation-map as indicated by `double-map'.
    ;; XXX I don't think key-translation-map should be made local here. -- Lorentey
    (make-local-variable 'key-translation-map)
    (let ((map (make-sparse-keymap)))
      (set-keymap-parent map key-translation-map)
      (setq key-translation-map map)
      (dolist (entry (append double-map '((magic-start) (magic-end))))
        (define-key map
          (vector (nth 0 entry)) 'double-translate-key)))))

(provide 'double)

;;; double.el ends here