;;; diff.el --- "DIFF" mode for handling output from unix diff utility.

;; Author: Frank P. Bresz <fpb@ittc.wec.com>
;; Maintainer: FSF
;; Created: 27 Jan 1989
;; Last-Modified: 21 Dec 1992

;; Copyright (C) 1990 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 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, 675 Mass Ave, Cambridge, MA 02139, USA.

;;; Commentary:

;; todo: diff-switches flexibility:
;; (defconst diff-switches-function
;;   '(lambda (file)
;;     (if (string-match "\\.el$" file)
;; 	 "-c -F\"^(\""
;;       "-p"))
;;  "Function to return switches to pass to the `diff' utility, in \\[diff].
;; This function is called with one arg, a file name, and returns a string
;; containing 0 or more arguments which are passed on to `diff'.
;; NOTE: This is not an ordinary hook; it may not be a list of functions.")

;;  - fpb@ittc.wec.com - Sep 25, 1990
;; Added code to support sccs diffing.
;; also fixed one minor glitch in the
;; search for the pattern.  If you only 1 addition you won't find the end
;; of the pattern (minor)

;;; Code:

(defvar diff-switches nil
  "*A list of switches to pass to the diff program.")

(defvar diff-search-pattern "^\\([0-9]\\|\\*\\*\\*\\*\\*\\*\\*\\*\\*\\*\\*\\*\\*\\*\\*\\)"
  "Regular expression that delineates difference regions in diffs.")

(defvar diff-rcs-extension ",v"
  "*Extension to find RCS file, some systems do not use ,v")

;; Initialize the keymap if it isn't already
(if (boundp 'diff-mode-map)
    nil
  (setq diff-mode-map (make-keymap))
  (suppress-keymap diff-mode-map)
  (define-key diff-mode-map "?" 'describe-mode)
  (define-key diff-mode-map "." 'diff-beginning-of-diff)
  (define-key diff-mode-map " " 'scroll-up)
  (define-key diff-mode-map "\177" 'scroll-down)
  (define-key diff-mode-map "n" 'diff-next-difference)
  (define-key diff-mode-map "p" 'diff-previous-difference)
  (define-key diff-mode-map "j" 'diff-show-difference))

;;;###autoload
(defun diff (old new)
  "Find and display the differences between OLD and NEW files.
Interactively the current buffer's file name is the default for for NEW
and a backup file for NEW is the default for OLD."
  (interactive
   (let (oldf newf)
     (reverse
      (list
       (setq newf (buffer-file-name)
	     newf (if (and newf (file-exists-p newf))
			  (read-file-name
			   (concat "Diff new file: ("
				   (file-name-nondirectory newf) ") ")
			   nil newf t)
			(read-file-name "Diff new file: " nil nil t)))
       (setq oldf (file-newest-backup newf)
	     oldf (if (and oldf (file-exists-p oldf))
			  (read-file-name
			   (concat "Diff original file: ("
				   (file-name-nondirectory oldf) ") ")
			   (file-name-directory oldf) oldf t)
			(read-file-name "Diff original file: "
					(file-name-directory newf) nil t)))))))
  (message "Comparing files %s %s..." new old)
  (setq new (expand-file-name new)
	old (expand-file-name old))
  (diff-internal-diff "diff" (append diff-switches (list new old)) nil))

(defun diff-sccs (new)
  "Find and display the differences between OLD and SCCS files."
  (interactive
   (let (newf)
      (list
       (setq newf (buffer-file-name)
	     newf (if (and newf (file-exists-p newf))
			  (read-file-name
			   (concat "Diff new file: ("
				   (file-name-nondirectory newf) ") ")
			   nil newf t)
			(read-file-name "Diff new file: " nil nil t))))))

  (message "Comparing SCCS file %s..." new)
  (setq new (expand-file-name new))
  (if (file-exists-p (concat
		      (file-name-directory new)
		      "SCCS/s."
		      (file-name-nondirectory new)))
      (diff-internal-diff "sccs"
			  (append '("diffs") diff-switches (list new))
			  2)
    (error "%s does not exist"
	   (concat (file-name-directory new) "SCCS/s."
		   (file-name-nondirectory new)))))

(defun diff-rcs (new)
  "Find and display the differences between OLD and RCS files."
  (interactive
   (let (newf)
      (list
       (setq newf (buffer-file-name)
	     newf (if (and newf (file-exists-p newf))
			  (read-file-name
			   (concat "Diff new file: ("
				   (file-name-nondirectory newf) ") ")
			   nil newf t)
			(read-file-name "Diff new file: " nil nil t))))))

  (message "Comparing RCS file %s..." new)
  (let* ((fullname (expand-file-name new))
       (rcsfile (concat (file-name-directory fullname)
                       "RCS/"
                       (file-name-nondirectory fullname)
                       diff-rcs-extension)))
    (if (file-exists-p rcsfile)
      (diff-internal-diff "rcsdiff" (append diff-switches (list fullname)) 4)
      (error "%s does not exist" rcsfile))))

(defun diff-internal-diff (diff-command sw strip)
  (let ((buffer-read-only nil))
    (with-output-to-temp-buffer "*Diff Output*"
      (buffer-disable-undo standard-output)
      (save-excursion
	(set-buffer standard-output)
	(erase-buffer)
	(apply 'call-process diff-command nil t nil sw)))
    (set-buffer "*Diff Output*")
    (goto-char (point-min))
    (while sw
      (if (string= (car sw) "-c")
	  ;; strip leading filenames from context diffs
	  (progn (forward-line 2) (delete-region (point-min) (point))))
      (if (and (string= (car sw) "-C") (string= "sccs" diff-command))
	  ;; strip stuff from SCCS context diffs
	  (progn (forward-line 2) (delete-region (point-min) (point))))
      (setq sw (cdr sw)))
    (if strip
	;; strip stuff from SCCS context diffs
	(progn (forward-line strip) (delete-region (point-min) (point)))))
  (diff-mode)
  (if (string= "0" diff-total-differences)
      (let ((buffer-read-only nil))
	(insert (message "There are no differences.")))
    (narrow-to-region (point) (progn
				(forward-line 1)
				(if (re-search-forward diff-search-pattern
						       nil t)
				    (goto-char (match-beginning 0))
				  (goto-char (point-max)))))
    (setq diff-current-difference "1")))

;; Take a buffer full of Unix diff output and go into a mode to easily
;; see the next and previous difference
(defun diff-mode ()
  "Diff Mode is used by \\[diff] for perusing the output from the diff program.
All normal editing commands are turned off.  Instead, these are available:
\\<diff-mode-map>
\\[diff-beginning-of-diff]	Move point to start of this difference.
\\[scroll-up]	Scroll to next screen of this difference.
\\[scroll-down]	Scroll to previous screen of this difference.
\\[diff-next-difference]	Move to Next Difference.
\\[diff-previous-difference]	Move to Previous Difference.
\\[diff-show-difference]	Jump to difference specified by numeric position.
"
  (interactive)
  (use-local-map diff-mode-map)
  (setq buffer-read-only t
	major-mode 'diff-mode
	mode-name "Diff"
	mode-line-modified "--- "
	mode-line-process
	'(" " diff-current-difference "/" diff-total-differences))
  (make-local-variable 'diff-current-difference)
  (set (make-local-variable 'diff-total-differences)
       (int-to-string (diff-count-differences))))

(defun diff-next-difference (n)
  "Go to the beginning of the next difference.
Differences are delimited by `diff-search-pattern'."
  (interactive "p")
  (if (< n 0) (diff-previous-difference (- n))
    (if (zerop n) ()
      (goto-char (point-min))
      (forward-line 1) ; to get past the match for the start of this diff
      (widen)
      (if (re-search-forward diff-search-pattern nil 'move n)
	  (let ((start (goto-char (match-beginning 0))))
	    (forward-line 1)
	    (if (re-search-forward diff-search-pattern nil 'move)
		(goto-char (match-beginning 0)))
	    (narrow-to-region start (point))
	    (setq diff-current-difference
		  (int-to-string (+ n (string-to-int
				       diff-current-difference)))))
	(re-search-backward diff-search-pattern nil)
	(narrow-to-region (point) (point-max))
	(message "No following differences.")
	(setq diff-current-difference diff-total-differences))
      (goto-char (point-min)))))

(defun diff-previous-difference (n)
  "Go the the beginning of the previous difference.
Differences are delimited by `diff-search-pattern'."
  (interactive "p")
  (if (< n 0) (diff-next-difference (- n))
    (if (zerop n) ()
      (goto-char (point-min))
      (widen)
      (if (re-search-backward diff-search-pattern nil 'move n)
	  (setq diff-current-difference
		(int-to-string (- (string-to-int diff-current-difference) n)))
	(message "No previous differences.")
	(setq diff-current-difference "1"))
      (narrow-to-region (point) (progn
				  (forward-line 1)
				  (re-search-forward diff-search-pattern nil)
				  (goto-char (match-beginning 0))))
      (goto-char (point-min)))))

(defun diff-show-difference (n)
  "Show difference number N (prefix argument)."
  (interactive "p")
  (let ((cur (string-to-int diff-current-difference)))
    (cond ((or (= n cur)
	       (zerop n)
	       (not (natnump n))) ; should signal an error perhaps.
	   ;; just redisplay.
	   (goto-char (point-min)))
	  ((< n cur)
	   (diff-previous-difference (- cur n)))
	  ((> n cur)
	   (diff-next-difference (- n cur))))))

(defun diff-beginning-of-diff ()
  "Go to beginning of current difference."
  (interactive)
  (goto-char (point-min)))

;; This function counts up the number of differences in the buffer.
(defun diff-count-differences ()
  "Count number of differences in the current buffer."
  (message "Counting differences...")
  (save-excursion
    (save-restriction
      (widen)
      (goto-char (point-min))
      (let ((cnt 0))
	(while (re-search-forward diff-search-pattern nil t)
	  (setq cnt (1+ cnt)))
	(message "Counting differences...done (%d)" cnt)
	cnt))))

;;; diff.el ends here