;;; paren.el --- highlight matching paren.

;; Copyright (C) 1993, 1996 Free Software Foundation, Inc.

;; Author: rms@gnu.ai.mit.edu
;; Maintainer: FSF
;; Keywords: languages, faces

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

;;; Commentary:

;; Load this and it will display highlighting on whatever
;; paren matches the one before or after point.

;;; Code:

(defgroup paren-showing nil
  "Showing (un)matching of parens and expressions."
  :prefix "show-paren-"
  :group 'paren-matching)

;; This is the overlay used to highlight the matching paren.
(defvar show-paren-overlay nil)
;; This is the overlay used to highlight the closeparen right before point.
(defvar show-paren-overlay-1 nil)

(defcustom show-paren-mode nil
  "Toggle Show Paren mode.
When Show Paren mode is enabled, any matching parenthesis is highlighted
after `show-paren-delay' seconds of Emacs idle time.
You must modify via \\[customize] for this variable to have an effect."
  :set (lambda (symbol value)
	 (show-paren-mode (or value 0)))
  :initialize 'custom-initialize-default
  :type 'boolean
  :group 'paren-showing
  :require 'paren)

(defcustom show-paren-style 'parenthesis
  "*Style used when showing a matching paren.
Valid styles are `parenthesis' (meaning show the matching paren),
`expression' (meaning show the entire expression enclosed by the paren) and
`mixed' (meaning show the matching paren if it is visible, and the expression
otherwise)."
  :type '(choice (const parenthesis) (const expression) (const mixed))
  :group 'paren-showing)

(defcustom show-paren-delay
  (if (featurep 'lisp-float-type) (/ (float 1) (float 8)) 1)
  "*Time in seconds to delay before showing a matching paren."
  :type '(number :tag "seconds")
  :group 'paren-showing)

(defface show-paren-match-face
  '((((class color)) (:background "turquoise"))
    (t (:background "gray")))
  "Show Paren mode face used for a matching paren."
  :group 'faces
  :group 'paren-showing)

(defface show-paren-mismatch-face
  '((((class color)) (:foreground "white" :background "purple"))
    (t (:reverse-video t)))
  "Show Paren mode face used for a mismatching paren."
  :group 'faces
  :group 'paren-showing)

(defvar show-paren-idle-timer nil)

;;;###autoload
(defun show-paren-mode (&optional arg)
  "Toggle Show Paren mode.
With prefix ARG, turn Show Paren mode on if and only if ARG is positive.
Returns the new status of Show Paren mode (non-nil means on).

When Show Paren mode is enabled, any matching parenthesis is highlighted
in `show-paren-style' after `show-paren-delay' seconds of Emacs idle time."
  (interactive "P")
  (when window-system
    (let ((on-p (if arg
		    (> (prefix-numeric-value arg) 0)
		  (not show-paren-mode))))
      (setq blink-matching-paren-on-screen (not on-p))
      (when show-paren-idle-timer
	(cancel-timer show-paren-idle-timer))
      (if on-p
	  (setq show-paren-idle-timer (run-with-idle-timer
				       show-paren-delay t
				       'show-paren-function))
	(and show-paren-overlay (overlay-buffer show-paren-overlay)
	     (delete-overlay show-paren-overlay))
	(and show-paren-overlay-1 (overlay-buffer show-paren-overlay-1)
	     (delete-overlay show-paren-overlay-1)))
      (setq show-paren-mode on-p))))

;; Find the place to show, if there is one,
;; and show it until input arrives.
(defun show-paren-function ()
  ;; Do nothing if no window system to display results with.
  ;; Do nothing if executing keyboard macro.
  ;; Do nothing if input is pending.
  (when window-system
    (let (pos dir mismatch face (oldpos (point)))
      (cond ((eq (char-syntax (preceding-char)) ?\))
	     (setq dir -1))
	    ((eq (char-syntax (following-char)) ?\()
	     (setq dir 1)))
      ;;
      ;; Find the other end of the sexp.
      (when dir
	(save-excursion
	  (save-restriction
	    ;; Determine the range within which to look for a match.
	    (when blink-matching-paren-distance
	      (narrow-to-region
	       (max (point-min) (- (point) blink-matching-paren-distance))
	       (min (point-max) (+ (point) blink-matching-paren-distance))))
	    ;; Scan across one sexp within that range.
	    ;; Errors or nil mean there is a mismatch.
	    (condition-case ()
		(setq pos (scan-sexps (point) dir))
	      (error (setq pos t mismatch t)))
	    ;; If found a "matching" paren, see if it is the right
	    ;; kind of paren to match the one we started at.
	    (when (integerp pos)
	      (let ((beg (min pos oldpos)) (end (max pos oldpos)))
		(when (/= (char-syntax (char-after beg)) ?\$)
		  (setq mismatch
			(not (eq (char-before end)
				 ;; This can give nil.
				 (matching-paren (char-after beg)))))))))))
      ;;
      ;; Highlight the other end of the sexp, or unhighlight if none.
      (if (not pos)
	  (progn
	    ;; If not at a paren that has a match,
	    ;; turn off any previous paren highlighting.
	    (and show-paren-overlay (overlay-buffer show-paren-overlay)
		 (delete-overlay show-paren-overlay))
	    (and show-paren-overlay-1 (overlay-buffer show-paren-overlay-1)
		 (delete-overlay show-paren-overlay-1)))
	;;
	;; Use the correct face.
	(if mismatch
	    (setq face 'show-paren-mismatch-face)
	  (setq face 'show-paren-match-face))
	;;
	;; If matching backwards, highlight the closeparen
	;; before point as well as its matching open.
	;; If matching forward, and the openparen is unbalanced,
	;; highlight the paren at point to indicate misbalance.
	;; Otherwise, turn off any such highlighting.
	(if (and (= dir 1) (integerp pos))
	    (when (and show-paren-overlay-1
		       (overlay-buffer show-paren-overlay-1))
	      (delete-overlay show-paren-overlay-1))
	  (let ((from (if (= dir 1)
			  (point)
			(forward-point -1)))
		(to (if (= dir 1)
			(forward-point 1)
		      (point))))
	    (if show-paren-overlay-1
		(move-overlay show-paren-overlay-1 from to (current-buffer))
	      (setq show-paren-overlay-1 (make-overlay from to)))
	    ;; Always set the overlay face, since it varies.
	    (overlay-put show-paren-overlay-1 'face face)))
	;;
	;; Turn on highlighting for the matching paren, if found.
	;; If it's an unmatched paren, turn off any such highlighting.
	(unless (integerp pos)
	  (delete-overlay show-paren-overlay))
	(let ((to (if (or (eq show-paren-style 'expression)
			  (and (eq show-paren-style 'mixed)
			       (not (pos-visible-in-window-p pos))))
		      (point)
		    pos))
	      (from (if (or (eq show-paren-style 'expression)
			    (and (eq show-paren-style 'mixed)
				 (not (pos-visible-in-window-p pos))))
			pos
		      (save-excursion
			(goto-char pos)
			(forward-point (- dir))))))
	  (if show-paren-overlay
	      (move-overlay show-paren-overlay from to (current-buffer))
	    (setq show-paren-overlay (make-overlay from to))))
	;;
	;; Always set the overlay face, since it varies.
	(overlay-put show-paren-overlay 'face face)))))

(provide 'paren)

(if show-paren-mode
    (show-paren-mode t))

;;; paren.el ends here