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

;; Copyright (C) 1993, 1994, 1997 Free Software Foundation, Inc.

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

;; This file is part of XEmacs.

;; XEmacs 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 2, or (at your option)
;; any later version.

;; XEmacs 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 XEmacs; see the file COPYING.  If not, write to the
;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.

;;; Commentary:

;;; Synched up with: FSF 20.2.

;; 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)

;;; Code:

(provide 'help-macro)

;;;###autoload
(defcustom three-step-help t
  "*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-appearance)

;;;###autoload
(defun help-read-key (prompt)
  (let (events)
    (while (not (key-press-event-p
		 (aref (setq events (read-key-sequence prompt)) 0)))
      ;; Mouse clicks are not part of the help feature, so reexecute
      ;; them in the standard environment.
      (mapc 'dispatch-event events))
    (let ((key (nconc (event-modifiers (aref events 0))
		      (list (event-key (aref events 0))))))
      ;; Make the HELP key translate to C-h.
      (when (lookup-key function-key-map key)
	(setq key (lookup-key function-key-map key)))
      (if (eq (length key) 1)
	  (car key)
	key))))

(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.
When FNAME finally does get a command, it executes that command
and then returns."
  `(defun ,fname ()
     ,help-text
     (interactive)
     (let ((line-prompt
	    (substitute-command-keys ,help-line)))
       (when three-step-help
	 (message "%s" line-prompt))
       (let* ((help-screen (documentation (quote ,fname)))
	      ;; 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))
	      (minor-mode-map-alist nil)
	      (prev-frame (selected-frame))
	      config new-frame key)
	 (unwind-protect
	     (progn
	       (set-keymap-parents local-map (list ,helped-map))
	       (cond (three-step-help
		      (let* ((overriding-local-map local-map))
			(setq key (help-read-key nil))))
		     (t
		      (setq key ??)))
	       (when (or (equal key ??)
			 (equal key (list help-char)))
		 (setq config (current-window-configuration))
		 (switch-to-buffer-other-window "*Help*")
		 (and (not (eq (window-frame (selected-window))
			       prev-frame))
		      (setq new-frame (window-frame (selected-window))
			    config nil))
		 (setq buffer-read-only nil)
		 (erase-buffer)
		 (insert help-screen)
		 (help-mode)
		 (goto-char (point-min))
		 (while (member key `((,help-char) ?? (control v) space ?\177
				      delete backspace (meta v)))
		   (ignore-errors
		     (cond ((member key '((control v) space))
			    (scroll-up))
			   ((member key '(?\177 delete (meta v) backspace))
			    (scroll-down))))
		   (let ((cursor-in-echo-area t)
			 (overriding-local-map local-map))
		     (setq key (help-read-key
				(format "Type one of the options listed%s: "
					(if (pos-visible-in-window-p
					     (point-max))
					    "" " or Space to scroll")))))))
	       ;; We don't need the prompt any more.
	       (message nil)
	       (let ((defn (lookup-key local-map key)))
		 (cond (defn
			 (when config
			   (set-window-configuration config)
			   (setq config nil))
			 (when new-frame
			   (iconify-frame new-frame)
			   (setq new-frame nil))
			 (call-interactively defn))
		       (t
			(ding)))))
	   (and (get-buffer "*Help*")
		(bury-buffer "*Help*"))
	   (and new-frame (iconify-frame new-frame))
	   (and config
		(set-window-configuration config)))))))

;;; help-macro.el