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

;; Copyright (C) 1993, 1996, 2001-2018 Free Software Foundation, Inc.

;; Author: rms@gnu.org
;; Maintainer: emacs-devel@gnu.org
;; 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 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 <https://www.gnu.org/licenses/>.

;;; Commentary:

;; Put this into your ~/.emacs:

;;  (show-paren-mode t)

;; 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)

(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)))

(defcustom show-paren-delay 0.125
  "Time in seconds to delay before showing a matching paren.
If you change this without using customize while `show-paren-mode' is
active, you must toggle the mode off and on again for this to take effect."
  :type '(number :tag "seconds")
  :initialize 'custom-initialize-default
  :set (lambda (sym val)
	 (if (not show-paren-mode)
	     (set sym val)
	   (show-paren-mode -1)
	   (set sym val)
	   (show-paren-mode 1))))

(defcustom show-paren-priority 1000
  "Priority of paren highlighting overlays."
  :type 'integer
  :version "21.1")

(defcustom show-paren-ring-bell-on-mismatch nil
  "If non-nil, beep if mismatched paren is detected."
  :type 'boolean
  :version "20.3")

(defcustom show-paren-when-point-inside-paren nil
  "If non-nil, show parens when point is just inside one.
This will only be done when point isn't also just outside a paren."
  :type 'boolean
  :version "25.1")

(defcustom show-paren-when-point-in-periphery nil
  "If non-nil, show parens when point is in the line's periphery.
The periphery is at the beginning or end of a line or in any
whitespace there."
  :type 'boolean
  :version "25.1")

(defcustom show-paren-highlight-openparen t
  "Non-nil turns on openparen highlighting when matching forward.
When nil, and point stands just before an open paren, the paren
is not highlighted, the cursor being regarded as adequate to mark
its position."
  :type 'boolean)

(defvar show-paren--idle-timer nil)
(defvar show-paren--overlay
  (let ((ol (make-overlay (point) (point) nil t))) (delete-overlay ol) ol)
  "Overlay used to highlight the matching paren.")
(defvar show-paren--overlay-1
  (let ((ol (make-overlay (point) (point) nil t))) (delete-overlay ol) ol)
  "Overlay used to highlight the paren at point.")


;;;###autoload
(define-minor-mode show-paren-mode
  "Toggle visualization of matching parens (Show Paren mode).

Show Paren mode is a global minor mode.  When enabled, any
matching parenthesis is highlighted in `show-paren-style' after
`show-paren-delay' seconds of Emacs idle time."
  :global t :group 'paren-showing
  ;; Enable or disable the mechanism.
  ;; First get rid of the old idle timer.
  (when show-paren--idle-timer
    (cancel-timer show-paren--idle-timer)
    (setq show-paren--idle-timer nil))
  (setq show-paren--idle-timer (run-with-idle-timer
                                show-paren-delay t
                                #'show-paren-function))
  (unless show-paren-mode
    (delete-overlay show-paren--overlay)
    (delete-overlay show-paren--overlay-1)))

(defun show-paren--unescaped-p (pos)
  "Determine whether the paren after POS is unescaped."
  (save-excursion
    (goto-char pos)
    (= (logand (skip-syntax-backward "/\\") 1) 0)))

(defun show-paren--categorize-paren (pos)
  "Determine whether the character after POS has paren syntax,
and if so, return a cons (DIR . OUTSIDE), where DIR is 1 for an
open paren, -1 for a close paren, and OUTSIDE is the buffer
position of the outside of the paren.  If the character isn't a
paren, or it is an escaped paren, return nil."
  (cond
   ((and (eq (syntax-class (syntax-after pos)) 4)
	 (show-paren--unescaped-p pos))
    (cons 1 pos))
   ((and (eq (syntax-class (syntax-after pos)) 5)
	 (show-paren--unescaped-p pos))
    (cons -1 (1+ pos)))))

(defun show-paren--locate-near-paren ()
  "Locate an unescaped paren \"near\" point to show.
If one is found, return the cons (DIR . OUTSIDE), where DIR is 1
for an open paren, -1 for a close paren, and OUTSIDE is the buffer
position of the outside of the paren.  Otherwise return nil."
  (let* ((ind-pos (save-excursion (back-to-indentation) (point)))
	 (eol-pos
	  (save-excursion
	    (end-of-line) (skip-chars-backward " \t" ind-pos) (point)))
	 (before (show-paren--categorize-paren (1- (point))))
	 (after (show-paren--categorize-paren (point))))
    (cond
     ;; Point is immediately outside a paren.
     ((eq (car before) -1) before)
     ((eq (car after) 1) after)
     ;; Point is immediately inside a paren.
     ((and show-paren-when-point-inside-paren before))
     ((and show-paren-when-point-inside-paren after))
     ;; Point is in the whitespace before the code.
     ((and show-paren-when-point-in-periphery
	   (<= (point) ind-pos))
      (or (show-paren--categorize-paren ind-pos)
	  (show-paren--categorize-paren (1- eol-pos))))
     ;; Point is in the whitespace after the code.
     ((and show-paren-when-point-in-periphery
	   (>= (point) eol-pos))
      (show-paren--categorize-paren (1- eol-pos))))))

(defvar show-paren-data-function #'show-paren--default
  "Function to find the opener/closer \"near\" point and its match.
The function is called with no argument and should return either nil
if there's no opener/closer near point, or a list of the form
\(HERE-BEG HERE-END THERE-BEG THERE-END MISMATCH)
Where HERE-BEG..HERE-END is expected to be near point.")

(defun show-paren--default ()
  "Finds the opener/closer near point and its match.

It is the default value of `show-paren-data-function'."
  (let* ((temp (show-paren--locate-near-paren))
	 (dir (car temp))
	 (outside (cdr temp))
	 pos mismatch here-beg here-end)
    ;;
    ;; Find the other end of the sexp.
    (when dir
      (setq here-beg (if (eq dir 1) outside (1- outside))
	    here-end (if (eq dir 1) (1+ outside) outside))
      (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 outside dir))
	  (error (setq pos t mismatch t)))
	;; Move back the other way and verify we get back to the
	;; starting point.  If not, these two parens don't really match.
	;; Maybe the one at point is escaped and doesn't really count,
	;; or one is inside a comment.
	(when (integerp pos)
	  (unless (condition-case ()
		      (eq outside (scan-sexps pos (- dir)))
		    (error nil))
	    (setq pos nil)))
	;; If found a "matching" paren, see if it is the right
	;; kind of paren to match the one we started at.
	(if (not (integerp pos))
	    (if mismatch (list here-beg here-end nil nil t))
	  (let ((beg (min pos outside)) (end (max pos outside)))
	    (unless (eq (syntax-class (syntax-after beg)) 8)
	      (setq mismatch
		    (not (or (eq (char-before end)
				 ;; This can give nil.
				 (cdr (syntax-after beg)))
			     (eq (char-after beg)
				 ;; This can give nil.
				 (cdr (syntax-after (1- end))))
			     ;; The cdr might hold a new paren-class
			     ;; info rather than a matching-char info,
			     ;; in which case the two CDRs should match.
			     (eq (cdr (syntax-after (1- end)))
				 (cdr (syntax-after beg)))))))
	    (list here-beg here-end
		  (if (= dir 1) (1- pos) pos)
		  (if (= dir 1) pos (1+ pos))
		  mismatch)))))))

(defun show-paren-function ()
  "Highlight the parentheses until the next input arrives."
  (let ((data (and show-paren-mode (funcall show-paren-data-function))))
    (if (not data)
        (progn
          ;; If show-paren-mode is nil in this buffer or if not at a paren that
          ;; has a match, turn off any previous paren highlighting.
          (delete-overlay show-paren--overlay)
          (delete-overlay show-paren--overlay-1))

      ;; Found something to highlight.
      (let* ((here-beg (nth 0 data))
             (here-end (nth 1 data))
             (there-beg (nth 2 data))
             (there-end (nth 3 data))
             (mismatch (nth 4 data))
             (highlight-expression
              (or (eq show-paren-style 'expression)
                  (and there-beg
                       (eq show-paren-style 'mixed)
                       (let ((closest (if (< there-beg here-beg)
                                          (1- there-end) (1+ there-beg))))
                         (not (pos-visible-in-window-p closest))))))
             (face
              (cond
               (mismatch
                (if show-paren-ring-bell-on-mismatch
                    (beep))
                'show-paren-mismatch)
               (highlight-expression 'show-paren-match-expression)
               (t 'show-paren-match))))
        ;;
        ;; 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 (or (not here-beg)
                (and (not show-paren-highlight-openparen)
		     (> here-end (point))
		     (<= here-beg (point))
                     (integerp there-beg)))
            (delete-overlay show-paren--overlay-1)
          (move-overlay show-paren--overlay-1
                        here-beg here-end (current-buffer))
          ;; Always set the overlay face, since it varies.
          (overlay-put show-paren--overlay-1 'priority show-paren-priority)
          (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.
        (if (not there-beg)
            (delete-overlay show-paren--overlay)
          (if highlight-expression
              (move-overlay show-paren--overlay
			    (if (< there-beg here-beg) here-end here-beg)
                            (if (< there-beg here-beg) there-beg there-end)
                            (current-buffer))
            (move-overlay show-paren--overlay
                          there-beg there-end (current-buffer)))
          ;; Always set the overlay face, since it varies.
          (overlay-put show-paren--overlay 'priority show-paren-priority)
          (overlay-put show-paren--overlay 'face face))))))

(provide 'paren)

;;; paren.el ends here