;;; help-macro.el --- makes command line help such as help-for-help  -*- lexical-binding: t -*-

;; Copyright (C) 1993-1994, 2001-2024 Free Software Foundation, Inc.

;; Author: Lynn Slater <lrs@indetech.com>
;; Maintainer: emacs-devel@gnu.org
;; Created: Mon Oct  1 11:42:39 1990
;; Adapted-By: ESR
;; Package: emacs

;; 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 file supplies the macro `make-help-screen' which constructs
;; single character dispatching with browsable help such as that
;; provided by `help-for-help'.  This can be used to make many modes
;; easier to use; for example, the (long-since defunct) GNU Emacs
;; Empire Tool used this for every "nested" mode map called from the
;; main mode map.

;;       The name of this package was changed from help-screen.el to
;; help-macro.el in order to fit in a 14-character limit.

;;-> ***********************  Example of use *********************************

;;->(make-help-screen help-for-empire-redistribute-map
;;->		  "c:civ m:mil p:population f:food ?"
;;->		  "You have discovered the GEET redistribution commands
;;->   From here, you can use the following options:
;;->
;;->c	Redistribute civs from overfull sectors into connected underfull ones
;;->	  The functions typically named by empire-ideal-civ-fcn control
;;->          based in part on empire-sector-civ-threshold
;;->m	Redistribute military using levels given by empire-ideal-mil-fcn
;;->p	Redistribute excess population to highways for max pop growth
;;->	  Excess is any sector so full babies will not be born.
;;->f	Even out food on highways to highway min and leave levels
;;->	  This is good to pump max food to all warehouses/dist pts
;;->
;;->
;;->Use \\[help-for-empire-redistribute-map] for help on redistribution.
;;->Use \\[help-for-empire-extract-map] for help on data extraction.
;;->Please use \\[describe-key] to find out more about any of the other keys."
;;->		  empire-shell-redistribute-map)

;;->  (define-key c-mp "\C-h" 'help-for-empire-redistribute-map)
;;->  (define-key c-mp help-character 'help-for-empire-redistribute-map)

;;; Code:

(require 'backquote)

;; This needs to be autoloaded because it is used in the
;; make-help-screen macro.  Using (bound-and-true-p three-step-help)
;; is not an acceptable alternative, because nothing loads help-macro
;; in a normal session, so any user customization would never be applied.
;;;###autoload
(defcustom three-step-help nil
  "Non-nil means give more info about Help command in three steps.
The three steps are simple prompt, prompt with all options, and
window listing and describing the options.
A value of nil means skip the middle step, so that \\[help-command] \\[help-command]
gives the window that lists the options."
  :type 'boolean
  :group 'help)

(defmacro make-help-screen (fname help-line help-text helped-map
                                  &optional buffer-name)
  "Construct help-menu function name FNAME.
When invoked, FNAME shows HELP-LINE and reads a command using HELPED-MAP.
If the command is the help character, FNAME displays HELP-TEXT
and continues trying to read a command using HELPED-MAP.
If HELP-TEXT contains the sequence `%THIS-KEY%', that is replaced
with the key sequence that invoked FNAME.
When FNAME finally does get a command, it executes that command
and then returns."
  (declare (indent defun))
  `(defun ,fname ()
     "Help command."
     (interactive)
     (let ((line-prompt
            (substitute-command-keys ,help-line))
           (help-buffer-under-preparation t))
       (when three-step-help
         (message "%s" line-prompt))
       (let* ((help-screen ,help-text)
              ;; We bind overriding-local-map for very small
              ;; sections, *excluding* where we switch buffers
              ;; and where we execute the chosen help command.
              (local-map (make-sparse-keymap))
              (new-minor-mode-map-alist minor-mode-map-alist)
              (prev-frame (selected-frame))
              config new-frame key char)
         (when (string-match "%THIS-KEY%" help-screen)
           (setq help-screen
                 (replace-match (help--key-description-fontified
                                 (substring (this-command-keys) 0 -1))
                                t t help-screen)))
         (unwind-protect
             (let ((minor-mode-map-alist nil))
               (setcdr local-map ,helped-map)
               (define-key local-map [t] 'undefined)
               ;; Make the scroll bar keep working normally.
               (define-key local-map [vertical-scroll-bar]
                 (lookup-key global-map [vertical-scroll-bar]))
               (if three-step-help
                   (progn
                     (setq key (let ((overriding-local-map local-map))
                                 (read-key-sequence nil)))
                     ;; Make the HELP key translate to C-h.
                     (if (lookup-key function-key-map key)
                         (setq key (lookup-key function-key-map key)))
                     (setq char (aref key 0)))
                 (setq char ??))
               (when (or (eq char ??) (eq char help-char)
                         (memq char help-event-list))
                 (setq config (current-window-configuration))
                 (pop-to-buffer (or ,buffer-name " *Metahelp*") nil t)
                 (and (fboundp 'make-frame)
                      (not (eq (window-frame)
                               prev-frame))
                      (setq new-frame (window-frame)
                            config nil))
                 (setq buffer-read-only nil)
                 (let ((inhibit-read-only t))
                   (erase-buffer)
                   (insert (substitute-command-keys help-screen)))
                 (let ((minor-mode-map-alist new-minor-mode-map-alist))
                   (help-mode)
                   (variable-pitch-mode)
                   (setq new-minor-mode-map-alist minor-mode-map-alist))
                 (goto-char (point-min))
                 (while (or (memq char (append help-event-list
                                               (cons help-char '( ?? ?\C-v ?\s ?\177 ?\M-v ?\S-\s
                                                                  deletechar backspace vertical-scroll-bar
                                                                  home end next prior up down))))
                            (eq (car-safe char) 'switch-frame)
                            (equal key "\M-v"))
                   (condition-case nil
                       (cond
                        ((eq (car-safe char) 'switch-frame)
                         (handle-switch-frame char))
                        ((memq char '(?\C-v ?\s next end))
                         (scroll-up))
                        ((or (memq char '(?\177 ?\M-v ?\S-\s deletechar backspace prior home))
                             (equal key "\M-v"))
                         (scroll-down))
                        ((memq char '(down))
                         (scroll-up 1))
                        ((memq char '(up))
                         (scroll-down 1)))
                     (error nil))
                   (let ((cursor-in-echo-area t)
                         (overriding-local-map local-map))
                     (setq key (read-key-sequence
                                (format "Type one of listed options%s: "
                                        (if (pos-visible-in-window-p
                                             (point-max))
                                            ""
                                          (concat  ", or "
                                                   (help--key-description-fontified (kbd "<PageDown>"))
                                                   "/"
                                                   (help--key-description-fontified (kbd "<PageUp>"))
                                                   "/"
                                                   (help--key-description-fontified (kbd "SPC"))
                                                   "/"
                                                   (help--key-description-fontified (kbd "DEL"))
                                                   " to scroll"))))
                           char (aref key 0)))

                   ;; If this is a scroll bar command, just run it.
                   (when (eq char 'vertical-scroll-bar)
                     (command-execute (lookup-key local-map key) nil key))))
               ;; We don't need the prompt any more.
               (message "")
               ;; Mouse clicks are not part of the help feature,
               ;; so reexecute them in the standard environment.
               (if (listp char)
                   (setq unread-command-events
                         (cons char unread-command-events)
                         config nil)
                 (let ((defn (lookup-key local-map key)))
                   (if defn
                       (progn
                         (when config
                           (set-window-configuration config)
                           (setq config nil))
                         ;; Temporarily rebind `minor-mode-map-alist'
                         ;; to `new-minor-mode-map-alist' (Bug#10454).
                         (let ((minor-mode-map-alist new-minor-mode-map-alist))
                           ;; `defn' must make sure that its frame is
                           ;; selected, so we won't iconify it below.
                           (call-interactively defn))
                         (when new-frame
                           ;; Do not iconify the selected frame.
                           (unless (eq new-frame (selected-frame))
                             (iconify-frame new-frame))
                           (setq new-frame nil)))
                     (unless (equal (key-description key) "C-g")
                       (message (substitute-command-keys
                                (format "No help command is bound to `\\`%s''"
                                        (key-description key))))
                       (ding))))))
           (when config
             (set-window-configuration config))
           (when new-frame
             (iconify-frame new-frame))
           (setq minor-mode-map-alist new-minor-mode-map-alist))))))

(provide 'help-macro)

;;; help-macro.el ends here
