;;; help-macro.el --- makes command line help such as help-for-help

;; Copyright (C) 1993-1994, 2001-2017 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 <http://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 GNU Emacs Empire Tool uses 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)

;;; Change Log:
;;
;; 22-Jan-1991		Lynn Slater x2048
;;    Last Modified: Mon Oct  1 11:43:52 1990 #3 (Lynn Slater)
;;    documented better

;;; 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)
  "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."
  (let ((doc-fn (intern (concat (symbol-name fname) "-doc"))))
    `(progn
       (defun ,doc-fn () ,help-text nil)
       (defun ,fname ()
	 "Help command."
	 (interactive)
	 (let ((line-prompt
		(substitute-command-keys ,help-line)))
	   (when three-step-help
	     (message "%s" line-prompt))
	   (let* ((help-screen (documentation (quote ,doc-fn)))
		  ;; 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 (key-description
				     (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 " *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 help-screen))
		     (let ((minor-mode-map-alist new-minor-mode-map-alist))
		       (help-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 delete backspace vertical-scroll-bar ?\M-v))))
				(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))
			     (scroll-up))
			    ((or (memq char '(?\177 ?\M-v delete backspace))
				 (equal key "\M-v"))
			     (scroll-down)))
			 (error nil))
		       (let ((cursor-in-echo-area t)
			     (overriding-local-map local-map))
			 (setq key (read-key-sequence
				    (format "Type one of the options listed%s: "
					    (if (pos-visible-in-window-p
						 (point-max))
						"" ", or SPACE or 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)))
			 (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
