;;; shr.el --- Simple HTML Renderer

;; Copyright (C) 2010 Free Software Foundation, Inc.

;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org>
;; Keywords: html

;; 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 <http://www.gnu.org/licenses/>.

;;; Commentary:

;; This package takes a HTML parse tree (as provided by
;; libxml-parse-html-region) and renders it in the current buffer.  It
;; does not do CSS, JavaScript or anything advanced: It's geared
;; towards rendering typical short snippets of HTML, like what you'd
;; find in HTML email and the like.

;;; Code:

(eval-when-compile (require 'cl))
(require 'browse-url)

(defgroup shr nil
  "Simple HTML Renderer"
  :group 'mail)

(defcustom shr-max-image-proportion 0.9
  "How big pictures displayed are in relation to the window they're in.
A value of 0.7 means that they are allowed to take up 70% of the
width and height of the window.  If they are larger than this,
and Emacs supports it, then the images will be rescaled down to
fit these criteria."
  :version "24.1"
  :group 'shr
  :type 'float)

(defcustom shr-blocked-images nil
  "Images that have URLs matching this regexp will be blocked."
  :version "24.1"
  :group 'shr
  :type 'regexp)

(defvar shr-content-function nil
  "If bound, this should be a function that will return the content.
This is used for cid: URLs, and the function is called with the
cid: URL as the argument.")

(defvar shr-width 70
  "Frame width to use for rendering.")

;;; Internal variables.

(defvar shr-folding-mode nil)
(defvar shr-state nil)
(defvar shr-start nil)
(defvar shr-indentation 0)
(defvar shr-inhibit-images nil)
(defvar shr-list-mode nil)
(defvar shr-content-cache nil)

(defvar shr-map
  (let ((map (make-sparse-keymap)))
    (define-key map "a" 'shr-show-alt-text)
    (define-key map "i" 'shr-browse-image)
    (define-key map "I" 'shr-insert-image)
    (define-key map "u" 'shr-copy-url)
    (define-key map "v" 'shr-browse-url)
    (define-key map "\r" 'shr-browse-url)
    map))

;; Public functions and commands.

;;;###autoload
(defun shr-insert-document (dom)
  (setq shr-content-cache nil)
  (let ((shr-state nil)
	(shr-start nil))
    (shr-descend (shr-transform-dom dom))))

(defun shr-copy-url ()
  "Copy the URL under point to the kill ring.
If called twice, then try to fetch the URL and see whether it
redirects somewhere else."
  (interactive)
  (let ((url (get-text-property (point) 'shr-url)))
    (cond
     ((not url)
      (message "No URL under point"))
     ;; Resolve redirected URLs.
     ((equal url (car kill-ring))
      (url-retrieve
       url
       (lambda (a)
	 (when (and (consp a)
		    (eq (car a) :redirect))
	   (with-temp-buffer
	     (insert (cadr a))
	     (goto-char (point-min))
	     ;; Remove common tracking junk from the URL.
	     (when (re-search-forward ".utm_.*" nil t)
	       (replace-match "" t t))
	     (message "Copied %s" (buffer-string))
	     (copy-region-as-kill (point-min) (point-max)))))))
     ;; Copy the URL to the kill ring.
     (t
      (with-temp-buffer
	(insert url)
	(copy-region-as-kill (point-min) (point-max))
	(message "Copied %s" url))))))

(defun shr-show-alt-text ()
  "Show the ALT text of the image under point."
  (interactive)
  (let ((text (get-text-property (point) 'shr-alt)))
    (if (not text)
	(message "No image under point")
      (message "%s" text))))

(defun shr-browse-image ()
  "Browse the image under point."
  (interactive)
  (let ((url (get-text-property (point) 'shr-image)))
    (if (not url)
	(message "No image under point")
      (message "Browsing %s..." url)
      (browse-url url))))

(defun shr-insert-image ()
  "Insert the image under point into the buffer."
  (interactive)
  (let ((url (get-text-property (point) 'shr-image)))
    (if (not url)
	(message "No image under point")
      (message "Inserting %s..." url)
      (url-retrieve url 'shr-image-fetched
		    (list (current-buffer) (1- (point)) (point-marker))
		    t))))

;;; Utility functions.

(defun shr-transform-dom (dom)
  (let ((result (list (pop dom))))
    (dolist (arg (pop dom))
      (push (cons (intern (concat ":" (symbol-name (car arg))) obarray)
		  (cdr arg))
	    result))
    (dolist (sub dom)
      (if (stringp sub)
	  (push (cons :text sub) result)
	(push (shr-transform-dom sub) result)))
    (nreverse result)))

(defun shr-descend (dom)
  (let ((function (intern (concat "shr-tag-" (symbol-name (car dom))) obarray)))
    (if (fboundp function)
	(funcall function (cdr dom))
      (shr-generic (cdr dom)))))

(defun shr-generic (cont)
  (dolist (sub cont)
    (cond
     ((eq (car sub) :text)
      (shr-insert (cdr sub)))
     ((listp (cdr sub))
      (shr-descend sub)))))

(defun shr-insert (text)
  (when (eq shr-state 'image)
    (insert "\n")
    (setq shr-state nil))
  (cond
   ((eq shr-folding-mode 'none)
    (insert text))
   (t
    (let ((first t)
	  column)
      (when (and (string-match "\\`[ \t\n]" text)
		 (not (bolp))
		 (not (eq (char-after (1- (point))) ? )))
	(insert " "))
      (dolist (elem (split-string text))
	(when (and (bolp)
		   (> shr-indentation 0))
	  (shr-indent))
	;; The shr-start is a special variable that is used to pass
	;; upwards the first point in the buffer where the text really
	;; starts.
	(unless shr-start
	  (setq shr-start (point)))
	(insert elem)
	(when (> (current-column) shr-width)
	  (if (not (search-backward " " (line-beginning-position) t))
	      (insert "\n")
	    (delete-char 1)
	    (insert "\n")
	    (put-text-property (1- (point)) (point) 'shr-break t)
	    (when (> shr-indentation 0)
	      (shr-indent))
	    (end-of-line)))
	(insert " "))
      (unless (string-match "[ \t\n]\\'" text)
	(delete-char -1))))))

(defun shr-ensure-newline ()
  (unless (zerop (current-column))
    (insert "\n")))

(defun shr-ensure-paragraph ()
  (unless (bobp)
    (if (bolp)
	(unless (save-excursion
		  (forward-line -1)
		  (looking-at " *$"))
	  (insert "\n"))
      (if (save-excursion
	    (beginning-of-line)
	    (looking-at " *$"))
	  (insert "\n")
	(insert "\n\n")))))

(defun shr-indent ()
  (insert (make-string shr-indentation ? )))

(defun shr-fontize-cont (cont &rest types)
  (let (shr-start)
    (shr-generic cont)
    (dolist (type types)
      (shr-add-font (or shr-start (point)) (point) type))))

(defun shr-add-font (start end type)
  (let ((overlay (make-overlay start end)))
    (overlay-put overlay 'face type)))

(defun shr-browse-url ()
  "Browse the URL under point."
  (interactive)
  (let ((url (get-text-property (point) 'shr-url)))
    (if (not url)
	(message "No link under point")
      (browse-url url))))

(defun shr-image-fetched (status buffer start end)
  (when (and (buffer-name buffer)
	     (not (plist-get status :error)))
    (url-store-in-cache (current-buffer))
    (when (or (search-forward "\n\n" nil t)
	      (search-forward "\r\n\r\n" nil t))
      (let ((data (buffer-substring (point) (point-max))))
        (with-current-buffer buffer
          (let ((alt (buffer-substring start end))
		(inhibit-read-only t))
	    (delete-region start end)
	    (shr-put-image data start alt))))))
  (kill-buffer (current-buffer)))

(defun shr-put-image (data point alt)
  (if (not (display-graphic-p))
      (insert alt)
    (let ((image (ignore-errors
		   (shr-rescale-image data))))
      (when image
	(put-image image point alt)))))

(defun shr-rescale-image (data)
  (if (or (not (fboundp 'imagemagick-types))
	  (not (get-buffer-window (current-buffer))))
      (create-image data nil t)
    (let* ((image (create-image data nil t))
	   (size (image-size image t))
	   (width (car size))
	   (height (cdr size))
	   (edges (window-inside-pixel-edges
		   (get-buffer-window (current-buffer))))
	   (window-width (truncate (* shr-max-image-proportion
				      (- (nth 2 edges) (nth 0 edges)))))
	   (window-height (truncate (* shr-max-image-proportion
				       (- (nth 3 edges) (nth 1 edges)))))
	   scaled-image)
      (when (> height window-height)
	(setq image (or (create-image data 'imagemagick t
				      :height window-height)
			image))
	(setq size (image-size image t)))
      (when (> (car size) window-width)
	(setq image (or
		     (create-image data 'imagemagick t
				   :width window-width)
		     image)))
      image)))

(defun shr-get-image-data (url)
  "Get image data for URL.
Return a string with image data."
  (with-temp-buffer
    (mm-disable-multibyte)
    (when (ignore-errors
	    (url-cache-extract (url-cache-create-filename url))
	    t)
      (when (or (search-forward "\n\n" nil t)
		(search-forward "\r\n\r\n" nil t))
	(buffer-substring (point) (point-max))))))

(defun shr-heading (cont &rest types)
  (shr-ensure-paragraph)
  (apply #'shr-fontize-cont cont types)
  (shr-ensure-paragraph))

;;; Tag-specific rendering rules.

(defun shr-tag-p (cont)
  (shr-ensure-paragraph)
  (shr-generic cont)
  (shr-ensure-paragraph))

(defun shr-tag-b (cont)
  (shr-fontize-cont cont 'bold))

(defun shr-tag-i (cont)
  (shr-fontize-cont cont 'italic))

(defun shr-tag-em (cont)
  (shr-fontize-cont cont 'bold))

(defun shr-tag-u (cont)
  (shr-fontize-cont cont 'underline))

(defun shr-tag-s (cont)
  (shr-fontize-cont cont 'strike-through))

(defun shr-tag-a (cont)
  (let ((url (cdr (assq :href cont)))
	(start (point))
	shr-start)
    (shr-generic cont)
    (widget-convert-button
     'link (or shr-start start) (point)
     :help-echo url)
    (put-text-property (or shr-start start) (point) 'keymap shr-map)
    (put-text-property (or shr-start start) (point) 'shr-url url)))

(defun shr-tag-img (cont)
  (when (and (> (current-column) 0)
	     (not (eq shr-state 'image)))
    (insert "\n"))
  (let ((start (point-marker)))
    (let ((alt (cdr (assq :alt cont)))
	  (url (cdr (assq :src cont))))
      (when (zerop (length alt))
	(setq alt "[img]"))
      (cond
       ((and (not shr-inhibit-images)
	     (string-match "\\`cid:" url))
	(let ((url (substring url (match-end 0)))
	      image)
	  (if (or (not shr-content-function)
		  (not (setq image (funcall shr-content-function url))))
	      (insert alt)
	    (shr-put-image image (point) alt))))
       ((or shr-inhibit-images
	    (and shr-blocked-images
		 (string-match shr-blocked-images url)))
	(setq shr-start (point))
	(let ((shr-state 'space))
	  (if (> (length alt) 8)
	      (shr-insert (substring alt 0 8))
	    (shr-insert alt))))
       ((url-is-cached (browse-url-url-encode-chars url "[&)$ ]"))
	(shr-put-image (shr-get-image-data url) (point) alt))
       (t
	(insert alt)
	(ignore-errors
	  (url-retrieve url 'shr-image-fetched
			(list (current-buffer) start (point-marker))
			t))))
      (insert " ")
      (put-text-property start (point) 'keymap shr-map)
      (put-text-property start (point) 'shr-alt alt)
      (put-text-property start (point) 'shr-image url)
      (setq shr-state 'image))))

(defun shr-tag-pre (cont)
  (let ((shr-folding-mode 'none))
    (shr-ensure-newline)
    (shr-generic cont)
    (shr-ensure-newline)))

(defun shr-tag-blockquote (cont)
  (shr-ensure-paragraph)
  (let ((shr-indentation (+ shr-indentation 4)))
    (shr-generic cont))
  (shr-ensure-paragraph))

(defun shr-tag-ul (cont)
  (shr-ensure-paragraph)
  (let ((shr-list-mode 'ul))
    (shr-generic cont))
  (shr-ensure-paragraph))

(defun shr-tag-ol (cont)
  (shr-ensure-paragraph)
  (let ((shr-list-mode 1))
    (shr-generic cont))
  (shr-ensure-paragraph))

(defun shr-tag-li (cont)
  (shr-ensure-newline)
  (let* ((bullet
	  (if (numberp shr-list-mode)
	      (prog1
		  (format "%d " shr-list-mode)
		(setq shr-list-mode (1+ shr-list-mode)))
	    "* "))
	 (shr-indentation (+ shr-indentation (length bullet))))
    (insert bullet)
    (shr-generic cont)))

(defun shr-tag-br (cont)
  (unless (bobp)
    (insert "\n"))
  (shr-generic cont))

(defun shr-tag-h1 (cont)
  (shr-heading cont 'bold 'underline))

(defun shr-tag-h2 (cont)
  (shr-heading cont 'bold))

(defun shr-tag-h3 (cont)
  (shr-heading cont 'italic))

(defun shr-tag-h4 (cont)
  (shr-heading cont))

(defun shr-tag-h5 (cont)
  (shr-heading cont))

(defun shr-tag-h6 (cont)
  (shr-heading cont))

(defun shr-tag-hr (cont)
  (shr-ensure-newline)
  (insert (make-string shr-width ?-) "\n"))

;;; Table rendering algorithm.

;; Table rendering is the only complicated thing here.  We do this by
;; first counting how many TDs there are in each TR, and registering
;; how wide they think they should be ("width=45%", etc).  Then we
;; render each TD separately (this is done in temporary buffers, so
;; that we can use all the rendering machinery as if we were in the
;; main buffer).  Now we know how much space each TD really takes, so
;; we then render everything again with the new widths, and finally
;; insert all these boxes into the main buffer.
(defun shr-tag-table (cont)
  (shr-ensure-paragraph)
  (setq cont (or (cdr (assq 'tbody cont))
		 cont))
  (let* ((shr-inhibit-images t)
	 ;; Find all suggested widths.
	 (columns (shr-column-specs cont))
	 ;; Compute how many characters wide each TD should be.
	 (suggested-widths (shr-pro-rate-columns columns))
	 ;; Do a "test rendering" to see how big each TD is (this can
	 ;; be smaller (if there's little text) or bigger (if there's
	 ;; unbreakable text).
	 (sketch (shr-make-table cont suggested-widths))
	 (sketch-widths (shr-table-widths sketch suggested-widths)))
    ;; Then render the table again with these new "hard" widths.
    (shr-insert-table (shr-make-table cont sketch-widths t) sketch-widths))
  ;; Finally, insert all the images after the table.  The Emacs buffer
  ;; model isn't strong enough to allow us to put the images actually
  ;; into the tables.
  (dolist (elem (shr-find-elements cont 'img))
    (shr-tag-img (cdr elem))))

(defun shr-find-elements (cont type)
  (let (result)
    (dolist (elem cont)
      (cond ((eq (car elem) type)
	     (push elem result))
	    ((consp (cdr elem))
	     (setq result (nconc (shr-find-elements (cdr elem) type) result)))))
    (nreverse result)))

(defun shr-insert-table (table widths)
  (shr-insert-table-ruler widths)
  (dolist (row table)
    (let ((start (point))
	  (height (let ((max 0))
		    (dolist (column row)
		      (setq max (max max (cadr column))))
		    max)))
      (dotimes (i height)
	(shr-indent)
	(insert "|\n"))
      (dolist (column row)
	(goto-char start)
	(let ((lines (nth 2 column))
	      (overlay-lines (nth 3 column))
	      overlay overlay-line)
	  (dolist (line lines)
	    (setq overlay-line (pop overlay-lines))
	    (end-of-line)
	    (insert line "|")
	    (dolist (overlay overlay-line)
	      (let ((o (make-overlay (- (point) (nth 0 overlay) 1)
				     (- (point) (nth 1 overlay) 1)))
		    (properties (nth 2 overlay)))
		(while properties
		  (overlay-put o (pop properties) (pop properties)))))
	    (forward-line 1))
	  ;; Add blank lines at padding at the bottom of the TD,
	  ;; possibly.
	  (dotimes (i (- height (length lines)))
	    (end-of-line)
	    (insert (make-string (length (car lines)) ? ) "|")
	    (forward-line 1)))))
    (shr-insert-table-ruler widths)))

(defun shr-insert-table-ruler (widths)
  (shr-indent)
  (insert "+")
  (dotimes (i (length widths))
    (insert (make-string (aref widths i) ?-) ?+))
  (insert "\n"))

(defun shr-table-widths (table suggested-widths)
  (let* ((length (length suggested-widths))
	 (widths (make-vector length 0))
	 (natural-widths (make-vector length 0)))
    (dolist (row table)
      (let ((i 0))
	(dolist (column row)
	  (aset widths i (max (aref widths i)
			      (car column)))
	  (aset natural-widths i (max (aref natural-widths i)
				      (cadr column)))
	  (setq i (1+ i)))))
    (let ((extra (- (apply '+ (append suggested-widths nil))
		    (apply '+ (append widths nil))))
	  (expanded-columns 0))
      (when (> extra 0)
	(dotimes (i length)
	  ;; If the natural width is wider than the rendered width, we
	  ;; want to allow the column to expand.
	  (when (> (aref natural-widths i) (aref widths i))
	    (setq expanded-columns (1+ expanded-columns))))
	(dotimes (i length)
	  (when (> (aref natural-widths i) (aref widths i))
	    (aset widths i (min
			    (1+ (aref natural-widths i))
			    (+ (/ extra expanded-columns)
			       (aref widths i))))))))
    widths))

(defun shr-make-table (cont widths &optional fill)
  (let ((trs nil))
    (dolist (row cont)
      (when (eq (car row) 'tr)
	(let ((tds nil)
	      (columns (cdr row))
	      (i 0)
	      column)
	  (while (< i (length widths))
	    (setq column (pop columns))
	    (when (or (memq (car column) '(td th))
		      (null column))
	      (push (shr-render-td (cdr column) (aref widths i) fill)
		    tds)
	      (setq i (1+ i))))
	  (push (nreverse tds) trs))))
    (nreverse trs)))

(defun shr-render-td (cont width fill)
  (with-temp-buffer
    (let ((cache (cdr (assoc (cons width cont) shr-content-cache))))
      (if cache
	  (insert cache)
	(let ((shr-width width)
	      (shr-indentation 0))
	  (shr-generic cont))
	(delete-region
	 (point)
	 (+ (point)
	    (skip-chars-backward " \t\n")))
	(push (cons (cons width cont) (buffer-string))
	      shr-content-cache)))
    (goto-char (point-min))
    (let ((max 0))
      (while (not (eobp))
	(end-of-line)
	(setq max (max max (current-column)))
	(forward-line 1))
      (when fill
	(goto-char (point-min))
	;; If the buffer is totally empty, then put a single blank
	;; line here.
	(if (zerop (buffer-size))
	    (insert (make-string width ? ))
	  ;; Otherwise, fill the buffer.
	  (while (not (eobp))
	    (end-of-line)
	    (when (> (- width (current-column)) 0)
	      (insert (make-string (- width (current-column)) ? )))
	    (forward-line 1))))
      (if fill
	  (list max
		(count-lines (point-min) (point-max))
		(split-string (buffer-string) "\n")
		(shr-collect-overlays))
	(list max
	      (shr-natural-width))))))

(defun shr-natural-width ()
  (goto-char (point-min))
  (let ((current 0)
	(max 0))
    (while (not (eobp))
      (end-of-line)
      (setq current (+ current (current-column)))
      (unless (get-text-property (point) 'shr-break)
	(setq max (max max current)
	      current 0))
      (forward-line 1))
    max))

(defun shr-collect-overlays ()
  (save-excursion
    (goto-char (point-min))
    (let ((overlays nil))
      (while (not (eobp))
	(push (shr-overlays-in-region (point) (line-end-position))
	      overlays)
	(forward-line 1))
      (nreverse overlays))))

(defun shr-overlays-in-region (start end)
  (let (result)
    (dolist (overlay (overlays-in start end))
      (push (list (if (> start (overlay-start overlay))
		      (- end start)
		    (- end (overlay-start overlay)))
		  (if (< end (overlay-end overlay))
		      0
		    (- end (overlay-end overlay)))
		  (overlay-properties overlay))
	    result))
    (nreverse result)))

(defun shr-pro-rate-columns (columns)
  (let ((total-percentage 0)
	(widths (make-vector (length columns) 0)))
    (dotimes (i (length columns))
      (setq total-percentage (+ total-percentage (aref columns i))))
    (setq total-percentage (/ 1.0 total-percentage))
    (dotimes (i (length columns))
      (aset widths i (max (truncate (* (aref columns i)
				       total-percentage
				       (- shr-width (1+ (length columns)))))
			  10)))
    widths))

;; Return a summary of the number and shape of the TDs in the table.
(defun shr-column-specs (cont)
  (let ((columns (make-vector (shr-max-columns cont) 1)))
    (dolist (row cont)
      (when (eq (car row) 'tr)
	(let ((i 0))
	  (dolist (column (cdr row))
	    (when (memq (car column) '(td th))
	      (let ((width (cdr (assq :width (cdr column)))))
		(when (and width
			   (string-match "\\([0-9]+\\)%" width))
		  (aset columns i
			(/ (string-to-number (match-string 1 width))
			   100.0))))
	      (setq i (1+ i)))))))
    columns))

(defun shr-count (cont elem)
  (let ((i 0))
    (dolist (sub cont)
      (when (eq (car sub) elem)
	(setq i (1+ i))))
    i))

(defun shr-max-columns (cont)
  (let ((max 0))
    (dolist (row cont)
      (when (eq (car row) 'tr)
	(setq max (max max (+ (shr-count (cdr row) 'td)
			      (shr-count (cdr row) 'th))))))
    max))

(provide 'shr)

;;; shr.el ends here