;;; rmc.el --- read from a multiple choice question -*- lexical-binding: t -*-

;; Copyright (C) 2016-2021 Free Software Foundation, Inc.

;; Maintainer: emacs-devel@gnu.org

;; 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:

;;; Code:

(require 'seq)

(defun rmc--add-key-description (elem)
  (let* ((char (car elem))
         (name (cadr elem))
         (pos (seq-position name char))
         (desc (key-description (char-to-string char)))
         (graphical-terminal
          (display-supports-face-attributes-p
           '(:underline t) (window-frame)))
         (altered-name
          (cond
           ;; Not in the name string, or a special character.
           ((or (not pos)
                (member desc '("ESC" "TAB" "RET" "DEL" "SPC")))
            (format "[%s] %s"
                    (if graphical-terminal
                        (propertize desc 'face 'read-multiple-choice-face)
                      desc)
                    name))
           ;; The prompt character is in the name, so highlight
           ;; it on graphical terminals.
           (graphical-terminal
            (setq name (copy-sequence name))
            (put-text-property pos (1+ pos)
                               'face 'read-multiple-choice-face
                               name)
            name)
           ;; And put it in [bracket] on non-graphical terminals.
           (t
            (concat
             (substring name 0 pos)
             "["
             (upcase (substring name pos (1+ pos)))
             "]"
             (substring name (1+ pos)))))))
    (cons char altered-name)))

(defun rmc--show-help (prompt help-string show-help choices altered-names)
  (let* ((buf-name (if (stringp show-help)
                       show-help
                     "*Multiple Choice Help*"))
         (buf (get-buffer-create buf-name)))
    (if (stringp help-string)
        (with-help-window buf
          (with-current-buffer buf
            (insert help-string)))
      (with-help-window buf
        (with-current-buffer buf
          (erase-buffer)
          (pop-to-buffer buf)
          (insert prompt "\n\n")
          (let* ((columns (/ (window-width) 25))
                 (fill-column 21)
                 (times 0)
                 (start (point)))
            (dolist (elem choices)
              (goto-char start)
              (unless (zerop times)
                (if (zerop (mod times columns))
                    ;; Go to the next "line".
                    (goto-char (setq start (point-max)))
                  ;; Add padding.
                  (while (not (eobp))
                    (end-of-line)
                    (insert (make-string (max (- (* (mod times columns)
                                                    (+ fill-column 4))
                                                 (current-column))
                                              0)
                                         ?\s))
                    (forward-line 1))))
              (setq times (1+ times))
              (let ((text
                     (with-temp-buffer
                       (insert (format
                                "%c: %s\n"
                                (car elem)
                                (cdr (assq (car elem) altered-names))))
                       (fill-region (point-min) (point-max))
                       (when (nth 2 elem)
                         (let ((start (point)))
                           (insert (nth 2 elem))
                           (unless (bolp)
                             (insert "\n"))
                           (fill-region start (point-max))))
                       (buffer-string))))
                (goto-char start)
                (dolist (line (split-string text "\n"))
                  (end-of-line)
                  (if (bolp)
                      (insert line "\n")
                    (insert line))
                  (forward-line 1))))))))
    buf))

;;;###autoload
(defun read-multiple-choice (prompt choices &optional help-string show-help)
  "Ask user to select an entry from CHOICES, promting with PROMPT.
This function allows to ask the user a multiple-choice question.

CHOICES should be a list of the form (KEY NAME [DESCRIPTION]).
KEY is a character the user should type to select the entry.
NAME is a short name for the entry to be displayed while prompting
\(if there's no room, it might be shortened).
DESCRIPTION is an optional longer description of the entry; it will
be displayed in a help buffer if the user requests more help.  This
help description has a fixed format in columns.  For greater
flexibility, instead of passing a DESCRIPTION, the caller can pass
the optional argument HELP-STRING.  This argument is a string that
should contain a more detailed description of all of the possible
choices.  `read-multiple-choice' will display that description in a
help buffer if the user requests that.
If optional argument SHOW-HELP is non-nil, show the help screen
immediately, before any user input.  If SHOW-HELP is a string,
use it as the name of the help buffer.

This function translates user input into responses by consulting
the bindings in `query-replace-map'; see the documentation of
that variable for more information.  The relevant bindings for the
purposes of this function are `recenter', `scroll-up', `scroll-down',
and `edit'.
If the user types the `recenter', `scroll-up', or `scroll-down'
responses, the function performs the requested window recentering or
scrolling, and then asks the question again.  If the user enters `edit',
the function starts a recursive edit.  When the user exit the recursive
edit, the multiple-choice prompt gains focus again.

When `use-dialog-box' is t (the default), and the command using this
function was invoked via the mouse, this function pops up a GUI dialog
to collect the user input, but only if Emacs is capable of using GUI
dialogs.  Otherwise, the function will always use text-mode dialogs.

The return value is the matching entry from the CHOICES list.

Usage example:

\(read-multiple-choice \"Continue connecting?\"
                      \\='((?a \"always\")
                        (?s \"session only\")
                        (?n \"no\")))"
  (let* ((choices (if show-help choices (append choices '((?? "?")))))
         (altered-names (mapcar #'rmc--add-key-description choices))
         (full-prompt
          (format
           "%s (%s): "
           prompt
           (mapconcat (lambda (e) (cdr e)) altered-names ", ")))
         tchar buf wrong-char answer)
    (save-window-excursion
      (save-excursion
        (if show-help
            (setq buf (rmc--show-help prompt help-string show-help
                                   choices altered-names)))
	(while (not tchar)
	  (message "%s%s"
                   (if wrong-char
                       "Invalid choice.  "
                     "")
                   full-prompt)
          (setq tchar
                (if (and (display-popup-menus-p)
                         last-input-event ; not during startup
                         (consp last-nonmenu-event)
                         use-dialog-box)
                    (x-popup-dialog
                     t
                     (cons prompt
                           (mapcar
                            (lambda (elem)
                              (cons (capitalize (cadr elem))
                                    (car elem)))
                            choices)))
                  (condition-case nil
                      (let ((cursor-in-echo-area t))
                        (read-event))
                    (error nil))))
          (setq answer (lookup-key query-replace-map (vector tchar) t))
          (setq tchar
                (cond
                 ((eq answer 'recenter)
                  (recenter) t)
                 ((eq answer 'scroll-up)
                  (ignore-errors (scroll-up-command)) t)
                 ((eq answer 'scroll-down)
                  (ignore-errors (scroll-down-command)) t)
                 ((eq answer 'scroll-other-window)
                  (ignore-errors (scroll-other-window)) t)
                 ((eq answer 'scroll-other-window-down)
                  (ignore-errors (scroll-other-window-down)) t)
                 ((eq answer 'edit)
                  (save-match-data
                    (save-excursion
                      (message "%s"
                               (substitute-command-keys
                                "Recursive edit; type \\[exit-recursive-edit] to return to help screen"))
                      (recursive-edit))))
                 (t tchar)))
          (when (eq tchar t)
            (setq wrong-char nil
                  tchar nil))
          ;; The user has entered an invalid choice, so display the
          ;; help messages.
          (when (and (not (eq tchar nil))
                     (not (assq tchar choices)))
	    (setq wrong-char (not (memq tchar `(?? ,help-char)))
                  tchar nil)
            (when wrong-char
              (ding))
            (setq buf (rmc--show-help prompt help-string show-help
                                   choices altered-names))))))
    (when (buffer-live-p buf)
      (kill-buffer buf))
    (assq tchar choices)))

(provide 'rmc)

;;; rmc.el ends here