;;; map-ynp.el -- General-purpose boolean question-asker.
;;; Copyright (C) 1991 Free Software Foundation, Inc.
;;; Written by Roland McGrath.
;;;
;;; This program 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.
;;;
;;; This program 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.
;;;
;;; A copy of the GNU General Public License can be obtained from this
;;; program's author (send electronic mail to roland@ai.mit.edu) or from
;;; the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA
;;; 02139, USA.
;;;
;;; map-y-or-n-p is a general-purpose question-asking function.
;;; It asks a series of y/n questions (a la y-or-n-p), and decides to
;;; applies an action to each element of a list based on the answer.
;;; The nice thing is that you also get some other possible answers
;;; to use, reminiscent of query-replace: ! to answer y to all remaining
;;; questions; ESC or q to answer n to all remaining questions; . to answer
;;; y once and then n for the remainder; and you can get help with C-h.

(defun map-y-or-n-p-help (object objects action)
  (format "Type SPC or `y' to %s the current %s;
DEL or `n' to skip the current %s;
! to %s all remaining %s;
ESC or `q' to exit;
or . (period) to %s the current %s and exit."
	  action object object action objects action object))

;;;###autoload
(defun map-y-or-n-p (prompter actor list &optional help)
  "Ask a series of boolean questions.
Takes args PROMPTER ACTOR LIST, and optional arg HELP.

LIST is a list of objects, or a function of no arguments to return the next
object or nil.

PROMPTER is a function of one arg (an object from LIST),
which returns a string to be used as the prompt for that object.
If the return value is not a string, it is eval'd to get the answer.
So, it may be nil to ignore the object, t to act on the object without
asking the user, or a form to do a more complex prompt.
PROMPTER may instead be a string, in which case the prompt is
\(format PROMPTER OBJECT\).

ACTOR is a function of one arg (an object from LIST),
which gets called with each object that the user answers `yes' for.

If HELP is given, it is a list (OBJECT OBJECTS ACTION),
where OBJECT is a string giving the singular noun for an elt of LIST;
OBJECTS is the plural noun for elts of LIST, and ACTION is a transitive
verb describing ACTOR.  The default is \(\"object\" \"objects\" \"act on\"\).

At the prompts, the user may enter y, Y, or SPC to act on that object;
n, N, or DEL to skip that object; ! to act on all following objects;
ESC or q to exit (skip all following objects); . (period) to act on the
current object and then exit; or \\[help-command] to get help.

Returns the number of actions taken."
  (let ((old-help-form help-form)
	(help-form (cons 'map-y-or-n-p-help
			 (or help '("object" "objects" "act on"))))
	(actions 0)
	prompt
	char
	(next (if (or (symbolp list)
		      (subrp list)
		      (compiled-function-p list)
		      (and (consp list)
			   (eq (car list) 'lambda)))
		  list
		(function (lambda ()
			    (if list
				(prog1
				    (car list)
				  (setq list (cdr list)))
			      nil)))))
	elt)
    (if (stringp prompter)
	(setq prompter (` (lambda (object)
			    (format (, prompter) object)))))
    (while (setq elt (funcall next))
      (setq prompt (funcall prompter elt))
      (if (stringp prompt)
	  (progn
	    ;; Prompt the user about this object.
	    (let ((cursor-in-echo-area t))
	      (message "%s(y, n, ! ., q, or %s)"
		       prompt (key-description (char-to-string help-char)))
	      (setq char (read-char)))
	    (cond ((or (= ?q char)
		       (= ?\e char))
		   (setq next (function (lambda () nil))))
		  ((or (= ?y char)
		       (= ?Y char)
		       (= ?  char))
		   ;; Act on the object.
		   (let ((help-form old-help-form))
		     (funcall actor elt))
		   (setq actions (1+ actions)))
		  ((or (= ?n char)
		       (= ?N char)
		       (= ?\^? char))
		   ;; Skip the object.
		   )
		  ((= ?. char)
		   ;; Act on the object and then exit.
		   (funcall actor elt)
		   (setq actions (1+ actions)
			 next (function (lambda () nil))))
		  ((= ?! char)
		   ;; Act on this and all following objects.
		   (if (eval (funcall prompter elt))
		       (progn
			 (funcall actor elt)
			 (setq actions (1+ actions))))
		   (while (setq elt (funcall next))
		     (if (eval (funcall prompter elt))
			 (progn
			   (funcall actor elt)
			   (setq actions (1+ actions))))))
		  ((= ?? char)
		   (setq unread-command-char help-char)
		   (setq next (` (lambda ()
				   (setq next '(, next))
				   '(, elt)))))
		  (t
		   ;; Random char.
		   (message "Type %s for help."
			    (key-description (char-to-string help-char)))
		   (beep)
		   (sit-for 1)
		   (setq next (` (lambda ()
				   (setq next '(, next))
				   '(, elt)))))))
	(if (eval prompt)
	    (progn
	      (funcall actor elt)
	      (setq actions (1+ actions))))))
    ;; Clear the last prompt from the minibuffer.
    (message "")
    ;; Return the number of actions that were taken.
    actions))