;;; code for diff output

(defgroup diff-text-highlighting nil
  "No clue why I defined this, blindly copying hi-lock code."
  :group 'faces)

(defgroup diff-faces nil
  "Faces for diff output."
  :group 'diff-text-highlighting)

(defface diff-hide
  '((t (:weight bold :foreground "blue")))
  "Face for diff output."
  :group 'diff-faces)

(defface diff-less
  '((t (:weight bold :foreground "red")))
  "Face for diff output."
  :group 'diff-faces)

(defface diff-more
  '((t (:weight bold :foreground "green")))
  "Face for diff output."
  :group 'diff-faces)

(defface diff-head
  '((t (:weight bold :foreground "yellow")))
  "Face for diff output."
  :group 'diff-faces)

'(setq diff-removed-face 'diff-less
       diff-added-face 'diff-more
       diff-header-face 'diff-hide
       ;; diff-file-header-face 'diff-hide
       diff-hunk-header-face 'diff-hide
       ;; inheritance seems to not work
       diff-index-face 'diff-hide)

(defun diff-colorize (swap)
  "Colorize diff output old/new text as red/green.
Optional prefix arg SWAP to exchange red and green."
  ;; use text overlays because they work when read-only
  ;; color-regexp groups <---> color-faces items
  ;; diff-hide	dark blue for boring details
  ;; diff-head	bright yellow for file headers
  ;; char ??	depends on + or - initial char
  ;; diff-more	green for new text
  ;; diff-less	red for old text
  (interactive "P")
  (message "Colorizing ...")
  (dolist (face '(diff-hide diff-head diff-less diff-more))
    (remove-overlays nil nil 'face face))
  (save-excursion
    (goto-char (point-min))
    (let ((color-regexp "^\\(\
\\(@@.*\\)\\|\
\\(\\(---\\|\\+\\+\\+\\) \\([^\t\n]*\\)\t\\(.*\\)\\)\\|\
\\(\\([-+]\\)\\(.*\\)\\)\
\\)$")
	  (color-faces '(diff-hide
			 nil diff-hide ?? diff-head
			 nil diff-hide ??)))
      (while (search-forward-regexp color-regexp (point-max) t)
	(do ((n 2 (1+ n))
	     (color color-faces (cdr color)))
	    ((null color))
	  (when (and (car color)
		     (match-beginning n))
	    (overlay-put
	     (make-overlay (match-beginning n) (match-end n))
	     'face
	     (if (symbolp (car color))
		 (car color)
	       (when (cdr color)
		 (message "Colorizing %s ..."
			  (match-string-no-properties n)))
	       (cadr (assq (char-after (match-beginning 0))
			   (if swap
			       '((?+ diff-less) (?- diff-more))
			     '((?+ diff-more) (?- diff-less))))))))))))
  (message "Colorizing Done."))

;;; end code for diff output