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;; Copyright (C) 1986 Free Software Foundation, Inc.

;; 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 1, 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
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING.  If not, write to
;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.

(require 'electric)
(provide 'ehelp) 

(defvar electric-help-map ()
  "Keymap defining commands available whilst scrolling
through a buffer in electric-help-mode")

(put 'electric-help-undefined 'suppress-keymap t)
(if electric-help-map
  (let ((map (make-keymap)))
    (fillarray map 'electric-help-undefined)
    (define-key map (char-to-string meta-prefix-char) (copy-keymap map))
    (define-key map (char-to-string help-char) 'electric-help-help)
    (define-key map "?" 'electric-help-help)
    (define-key map " " 'scroll-up)
    (define-key map "\^?" 'scroll-down)
    (define-key map "." 'beginning-of-buffer)
    (define-key map "<" 'beginning-of-buffer)
    (define-key map ">" 'end-of-buffer)
    ;(define-key map "\C-g" 'electric-help-exit)
    (define-key map "q" 'electric-help-exit)
    (define-key map "Q" 'electric-help-exit)
    ;;a better key than this?
    (define-key map "r" 'electric-help-retain)

    (setq electric-help-map map)))
(defun electric-help-mode ()
  "with-electric-help temporarily places its buffer in this mode
\(On exit from with-electric-help, the buffer is put in default-major-mode)"
  (setq buffer-read-only t)
  (setq mode-name "Help")
  (setq major-mode 'help)
  (setq mode-line-buffer-identification '(" Help:  %b"))
  (use-local-map electric-help-map)
  ;; this is done below in with-electric-help
  ;(run-hooks 'electric-help-mode-hook)

(defun with-electric-help (thunk &optional buffer noerase)
  "Arguments are THUNK &optional BUFFER NOERASE.
BUFFER defaults to \"*Help*\"
THUNK is a function of no arguments which is called to initialise
 the contents of BUFFER.  BUFFER will be erased before THUNK is called unless
 NOERASE is non-nil.  THUNK will be called with  standard-output  bound to
 the buffer specified by BUFFER

After THUNK has been called, this function \"electrically\" pops up a window
in which BUFFER is displayed and allows the user to scroll through that buffer
in electric-help-mode.
When the user exits (with electric-help-exit, or otherwise) the help
buffer's window disappears (ie we use save-window-excursion)
BUFFER is put into default-major-mode (or fundamental-mode) when we exit"
  (setq buffer (get-buffer-create (or buffer "*Help*")))
  (let ((one (one-window-p t))
	(two nil))
	(if one (goto-char (window-start (selected-window))))
	(let ((pop-up-windows t))
	  (pop-to-buffer buffer))
		(set-buffer buffer)
		(setq buffer-read-only nil)
		(or noerase (erase-buffer)))
	      (let ((standard-output buffer))
		(if (funcall thunk)
		  (set-buffer buffer)
		  (set-buffer-modified-p nil)
		  (goto-char (point-min))
		  (if one (shrink-window-if-larger-than-buffer (selected-window)))))
	      (set-buffer buffer)
	      (run-hooks 'electric-help-mode-hook)
	      (setq two (electric-help-command-loop))
	      (cond ((eq (car-safe two) 'retain)
		     (setq two (vector (window-height (selected-window))
				       (window-start (selected-window))
				       (window-hscroll (selected-window))
		    (t (setq two nil))))
	  (message "")
	  (set-buffer buffer)
	  (setq buffer-read-only nil)
	  (condition-case ()
	      (funcall (or default-major-mode 'fundamental-mode))
	    (error nil)))))
    (if two
	(let ((pop-up-windows t)
	  (pop-to-buffer buffer)
	  (setq tem (- (window-height (selected-window)) (elt two 0)))
	  (if (> tem 0) (shrink-window tem))
	  (set-window-start (selected-window) (elt two 1) t)
	  (set-window-hscroll (selected-window) (elt two 2))
	  (goto-char (elt two 3)))
      ;;>> Perhaps this shouldn't be done.
      ;; so that when we say "Press space to bury" we mean it
      (replace-buffer-in-windows buffer)
      ;; must do this outside of save-window-excursion
      (bury-buffer buffer))))

(defun electric-help-command-loop ()
  (catch 'exit
    (if (pos-visible-in-window-p (point-max))
	(progn (message "<<< Press Space to bury the help buffer >>>")
	       (if (= (setq unread-command-char (read-char)) ?\  )
		   (progn (setq unread-command-char -1)
			  (throw 'exit t)))))
    (let (up down both neither
	  (standard (and (eq (key-binding " ")
			 (eq (key-binding "\^?")
			 (eq (key-binding "Q")
			 (eq (key-binding "q")
	(function (lambda ()
	  (let ((min (pos-visible-in-window-p (point-min)))
		(max (pos-visible-in-window-p (point-max))))
	    (cond ((and min max)
		   (cond (standard "Press Q to exit ")
			 (t (setq neither (substitute-command-keys "Press \\[scroll-up] to exit ")))))
		   (cond (standard "Press SPC to scroll, Q to exit ")
			 (t (setq up (substitute-command-keys "Press \\[scroll-up] to scroll; \\[electric-help-exit] to exit ")))))
		   (cond (standard "Press DEL to scroll back, Q to exit ")
			 (t (setq down (substitute-command-keys "Press \\[scroll-down] to scroll back, \\[scroll-up] to exit ")))))
		   (cond (standard "Press SPC to scroll, DEL to scroll back, Q to exit ")
			 (t (setq both (substitute-command-keys "Press \\[scroll-up] to scroll, \\[scroll-down] to scroll back, \\[electric-help-exit] to exit ")))))))))

;(defun electric-help-scroll-up (arg)
;  ">>>Doc"
;  (interactive "P")
;  (if (and (null arg) (pos-visible-in-window-p (point-max)))
;      (electric-help-exit)
;    (scroll-up arg)))

(defun electric-help-exit ()
  (throw 'exit t))

(defun electric-help-retain ()
  "Exit electric-help, retaining the current window/buffer conifiguration.
\(The *Help* buffer will not be selected, but \\[switch-to-buffer-other-window] RET
will select it.)"
  (throw 'exit '(retain)))

;(defun electric-help-undefined ()
;  (interactive)
;  (let* ((keys (this-command-keys))
;	 (n (length keys)))
;    (if (or (= n 1)
;	    (and (= n 2)
;		 meta-flag
;		 (eq (aref keys 0) meta-prefix-char)))
;	(setq unread-command-char last-input-char
;	      current-prefix-arg prefix-arg)
;      ;;>>> I don't care.
;      ;;>>> The emacs command-loop is too much pure pain to
;      ;;>>> duplicate
;      ))
;  (throw 'exit t))

(defun electric-help-undefined ()
  (error "%s is undefined -- Press %s to exit"
	 (mapconcat 'single-key-description (this-command-keys) " ")
	 (if (eq (key-binding "Q") 'electric-help-exit)
	   (substitute-command-keys "\\[electric-help-exit]"))))

;>>> this needs to be hairified (recursive help, anybody?)
(defun electric-help-help ()
  (if (and (eq (key-binding "Q") 'electric-help-exit)
	   (eq (key-binding " ") 'scroll-up)
	   (eq (key-binding "\^?") 'scroll-down))
      (message "SPC scrolls forward, DEL scrolls back, Q exits and burys help buffer")
    ;; to give something for user to look at while slow substitute-cmd-keys
    ;;  grinds away
    (message "Help...")
    (message "%s" (substitute-command-keys "\\[scroll-up] scrolls forward, \\[scroll-down] scrolls back, \\[electric-help-exit] exits.")))
  (sit-for 2))

(defun electric-helpify (fun)
  (let ((name "*Help*"))
    (if (save-window-excursion
	  ;; kludge-o-rama
	  (let* ((p (symbol-function 'print-help-return-message))
		 (b (get-buffer name))
		 (m (buffer-modified-p b)))
	    (and b (not (get-buffer-window b))
		 (setq b nil))
		  (message "%s..." (capitalize (symbol-name fun)))
		  ;; with-output-to-temp-buffer marks the buffer as unmodified.
		  ;; kludging excessively and relying on that as some sort
		  ;;  of indication leads to the following abomination...
		  ;;>> This would be doable without such icky kludges if either
		  ;;>> (a) there were a function to read the interactive
		  ;;>>     args for a command and return a list of those args.
		  ;;>>     (To which one would then just apply the command)
		  ;;>>     (The only problem with this is that interactive-p
		  ;;>>      would break, but that is such a misfeature in
		  ;;>>      any case that I don't care)
		  ;;>>     It is easy to do this for emacs-lisp functions;
		  ;;>>     the only problem is getting the interactive spec
		  ;;>>     for subrs
		  ;;>> (b) there were a function which returned a
		  ;;>>     modification-tick for a buffer.  One could tell
		  ;;>>     whether a buffer had changed by whether the
		  ;;>>     modification-tick were different.
		  ;;>>     (Presumably there would have to be a way to either
		  ;;>>      restore the tick to some previous value, or to
		  ;;>>      suspend updating of the tick in order to allow
		  ;;>>      things like momentary-string-display)
		  (and b
			 (set-buffer b)
			 (set-buffer-modified-p t)))
		  (fset 'print-help-return-message 'ignore)
		  (call-interactively fun)
		  (and (get-buffer name)
		       (get-buffer-window (get-buffer name))
		       (or (not b)
			   (not (eq b (get-buffer name)))
			   (not (buffer-modified-p b)))))
	      (fset 'print-help-return-message p)
	      (and b (buffer-name b)
		     (set-buffer b)
		     (set-buffer-modified-p m))))))
	(with-electric-help 'ignore name t))))

(defun electric-describe-key ()
  (electric-helpify 'describe-key))

(defun electric-describe-mode ()
  (electric-helpify 'describe-mode))

(defun electric-view-lossage ()
  (electric-helpify 'view-lossage))

;(defun electric-help-for-help ()
;  "See help-for-help"
;  (interactive)
;  )

(defun electric-describe-function ()
  (electric-helpify 'describe-function))

(defun electric-describe-variable ()
  (electric-helpify 'describe-variable))

(defun electric-describe-bindings ()
  (electric-helpify 'describe-bindings))

(defun electric-describe-syntax ()
  (electric-helpify 'describe-syntax))

(defun electric-command-apropos ()
  (electric-helpify 'command-apropos))

;(define-key help-map "a" 'electric-command-apropos)

;;;; ehelp-map

(defvar ehelp-map ())
(if ehelp-map
  (let ((map (copy-keymap help-map))) 
    (substitute-key-definition 'describe-key 'electric-describe-key map)
    (substitute-key-definition 'describe-mode 'electric-describe-mode map)
    (substitute-key-definition 'view-lossage 'electric-view-lossage map)
    (substitute-key-definition 'describe-function 'electric-describe-function map)
    (substitute-key-definition 'describe-variable 'electric-describe-variable map)
    (substitute-key-definition 'describe-bindings 'electric-describe-bindings map)
    (substitute-key-definition 'describe-syntax 'electric-describe-syntax map)

    (setq ehelp-map map)
    (fset 'ehelp-command map)))

;; Do (define-key global-map "\C-h" 'ehelp-command) if you want to win