emacs/lisp/gnus/html2text.el

;;; html2text.el --- a simple html to plain text converter -*- coding: utf-8 -*-

;; Copyright (C) 2002-2015 Free Software Foundation, Inc.

;; Author: Joakim Hove <hove@phys.ntnu.no>

;; 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:

;; These functions provide a simple way to wash/clean html infected
;; mails.  Definitely do not work in all cases, but some improvement
;; in readability is generally obtained.  Formatting is only done in
;; the buffer, so the next time you enter the article it will be
;; "re-htmlized".
;;
;; The main function is `html2text'.

;;; Code:

;;
;; <Global variables>
;;

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

(defvar html2text-format-single-element-list '(("hr" . html2text-clean-hr)))

(defvar html2text-replace-list
  '(("&acute;" . "`")
    ("&amp;" . "&")
    ("&apos;" . "'")
    ("&brvbar;" . "|")
    ("&cent;" . "c")
    ("&circ;" . "^")
    ("&copy;" . "(C)")
    ("&curren;" . "(#)")
    ("&deg;" . "degree")
    ("&divide;" . "/")
    ("&euro;" . "e")
    ("&frac12;" . "1/2")
    ("&gt;" . ">")
    ("&iquest;" . "?")
    ("&laquo;" . "<<")
    ("&ldquo" . "\"")
    ("&lsaquo;" . "(")
    ("&lsquo;" . "`")
    ("&lt;" . "<")
    ("&mdash;" . "--")
    ("&nbsp;" . " ")
    ("&ndash;" . "-")
    ("&permil;" . "%%")
    ("&plusmn;" . "+-")
    ("&pound;" . "£")
    ("&quot;" . "\"")
    ("&raquo;" . ">>")
    ("&rdquo" . "\"")
    ("&reg;" . "(R)")
    ("&rsaquo;" . ")")
    ("&rsquo;" . "'")
    ("&sect;" . "§")
    ("&sup1;" . "^1")
    ("&sup2;" . "^2")
    ("&sup3;" . "^3")
    ("&tilde;" . "~"))
  "The map of entity to text.

This is an alist were each element is a dotted pair consisting of an
old string, and a replacement string.  This replacement is done by the
function `html2text-substitute' which basically performs a
`replace-string' operation for every element in the list.  This is
completely verbatim - without any use of REGEXP.")

(defvar html2text-remove-tag-list
  '("html" "body" "p" "img" "dir" "head" "div" "br" "font" "title" "meta")
  "A list of removable tags.

This is a list of tags which should be removed, without any
formatting.  Note that tags in the list are presented *without*
any \"<\" or \">\".  All occurrences of a tag appearing in this
list are removed, irrespective of whether it is a closing or
opening tag, or if the tag has additional attributes.  The
deletion is done by the function `html2text-remove-tags'.

For instance the text:

\"Here comes something <font size\"+3\" face=\"Helvetica\"> big </font>.\"

will be reduced to:

\"Here comes something big.\"

If this list contains the element \"font\".")

(defvar html2text-format-tag-list
  '(("b" 	  . html2text-clean-bold)
    ("strong"     . html2text-clean-bold)
    ("u" 	  . html2text-clean-underline)
    ("i" 	  . html2text-clean-italic)
    ("em"         . html2text-clean-italic)
    ("blockquote" . html2text-clean-blockquote)
    ("a"          . html2text-clean-anchor)
    ("ul"         . html2text-clean-ul)
    ("ol"         . html2text-clean-ol)
    ("dl"         . html2text-clean-dl)
    ("center"     . html2text-clean-center))
  "An alist of tags and processing functions.

This is an alist where each dotted pair consists of a tag, and then
the name of a function to be called when this tag is found.  The
function is called with the arguments p1, p2, p3 and p4. These are
demonstrated below:

\"<b> This is bold text </b>\"
 ^   ^                 ^    ^
 |   |                 |    |
p1  p2                p3   p4

Then the called function will typically format the text somewhat and
remove the tags.")

(defvar html2text-remove-tag-list2  '("li" "dt" "dd" "meta")
  "Another list of removable tags.

This is a list of tags which are removed similarly to the list
`html2text-remove-tag-list' - but these tags are retained for the
formatting, and then moved afterward.")

;;
;; </Global variables>
;;

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;;
;; <Utility functions>
;;


(defun html2text-replace-string (from-string to-string min max)
  "Replace FROM-STRING with TO-STRING in region from MIN to MAX."
  (goto-char min)
  (let ((delta (- (string-width to-string) (string-width from-string)))
	(change 0))
    (while (search-forward from-string max t)
      (replace-match to-string)
      (setq change (+ change delta)))
    change))

;;
;; </Utility functions>
;;

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;;
;; <Functions related to attributes> i.e. <font size=+3>
;;

(defun html2text-attr-value (list attribute)
  "Get value of ATTRIBUTE from LIST."
  (nth 1 (assoc attribute list)))

(defun html2text-get-attr (p1 p2)
  (goto-char p1)
  (re-search-forward "\\s-+" p2 t)
  (let (attr-list)
    (while (re-search-forward "[-a-z0-9._]+" p2 t)
      (setq attr-list
	    (cons
	     (list (match-string 0)
		   (when (looking-at "\\s-*=")
		     (goto-char (match-end 0))
		     (skip-chars-forward "[:space:]")
		     (when (or (looking-at "\"[^\"]*\"\\|'[^']*'")
			       (looking-at "[-a-z0-9._:]+"))
		       (goto-char (match-end 0))
		       (match-string 0))))
	     attr-list)))
    attr-list))

;;
;; </Functions related to attributes>
;;

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;;
;; <Functions to be called to format a tag-pair>
;;
(defun html2text-clean-list-items (p1 p2 list-type)
  (goto-char p1)
  (let ((item-nr 0)
	(items   0))
    (while (search-forward "<li>" p2 t)
      (setq items (1+ items)))
    (goto-char p1)
    (while (< item-nr items)
      (setq item-nr (1+ item-nr))
      (search-forward "<li>" (point-max) t)
      (cond
       ((string= list-type "ul") (insert " o "))
       ((string= list-type "ol") (insert (format " %s: " item-nr)))
       (t (insert " x "))))))

(defun html2text-clean-dtdd (p1 p2)
  (goto-char p1)
  (let ((items   0)
	(item-nr 0))
    (while (search-forward "<dt>" p2 t)
      (setq items (1+ items)))
    (goto-char p1)
    (while (< item-nr items)
      (setq item-nr (1+ item-nr))
      (re-search-forward "<dt>\\([ ]*\\)" (point-max) t)
      (when (match-string 1)
	(delete-region (point) (- (point) (string-width (match-string 1)))))
      (let ((def-p1 (point))
	    (def-p2 0))
	(re-search-forward "\\([ ]*\\)\\(</dt>\\|<dd>\\)" (point-max) t)
	(if (match-string 1)
	    (progn
	      (let* ((mw1 (string-width (match-string 1)))
		     (mw2 (string-width (match-string 2)))
		     (mw  (+ mw1 mw2)))
		(goto-char (- (point) mw))
		(delete-region (point) (+ (point) mw1))
		(setq def-p2 (point))))
	  (setq def-p2 (- (point) (string-width (match-string 2)))))
	(put-text-property def-p1 def-p2 'face 'bold)))))

(defun html2text-delete-tags (p1 p2 p3 p4)
  (delete-region p1 p2)
  (delete-region (- p3 (- p2 p1)) (- p4 (- p2 p1))))

(defun html2text-delete-single-tag (p1 p2)
  (delete-region p1 p2))

(defun html2text-clean-hr (p1 p2)
  (html2text-delete-single-tag p1 p2)
  (goto-char p1)
  (newline 1)
  (insert (make-string fill-column ?-)))

(defun html2text-clean-ul (p1 p2 p3 p4)
  (html2text-delete-tags p1 p2 p3 p4)
  (html2text-clean-list-items p1 (- p3 (- p1 p2)) "ul"))

(defun html2text-clean-ol (p1 p2 p3 p4)
  (html2text-delete-tags p1 p2 p3 p4)
  (html2text-clean-list-items p1 (- p3 (- p1 p2)) "ol"))

(defun html2text-clean-dl (p1 p2 p3 p4)
  (html2text-delete-tags p1 p2 p3 p4)
  (html2text-clean-dtdd p1 (- p3 (- p1 p2))))

(defun html2text-clean-center (p1 p2 p3 p4)
  (html2text-delete-tags p1 p2 p3 p4)
  (center-region p1 (- p3 (- p2 p1))))

(defun html2text-clean-bold (p1 p2 p3 p4)
  (put-text-property p2 p3 'face 'bold)
  (html2text-delete-tags p1 p2 p3 p4))

(defun html2text-clean-title (p1 p2 p3 p4)
  (put-text-property p2 p3 'face 'bold)
  (html2text-delete-tags p1 p2 p3 p4))

(defun html2text-clean-underline (p1 p2 p3 p4)
  (put-text-property p2 p3 'face 'underline)
  (html2text-delete-tags p1 p2 p3 p4))

(defun html2text-clean-italic (p1 p2 p3 p4)
  (put-text-property p2 p3 'face 'italic)
  (html2text-delete-tags p1 p2 p3 p4))

(defun html2text-clean-font (p1 p2 p3 p4)
  (html2text-delete-tags p1 p2 p3 p4))

(defun html2text-clean-blockquote (p1 p2 p3 p4)
  (html2text-delete-tags p1 p2 p3 p4))

(defun html2text-clean-anchor (p1 p2 p3 p4)
  ;; If someone can explain how to make the URL clickable I will surely
  ;; improve upon this.
  ;; Maybe `goto-addr.el' can be used here.
  (let* ((attr-list (html2text-get-attr p1 p2))
	 (href (html2text-attr-value attr-list "href")))
    (delete-region p1 p4)
    (when href
      (goto-char p1)
      (insert (if (string-match "\\`['\"].*['\"]\\'" href)
		  (substring href 1 -1) href))
      (put-text-property p1 (point) 'face 'bold))))

;;
;; </Functions to be called to format a tag-pair>
;;

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;;
;; <Functions to be called to fix up paragraphs>
;;

(defun html2text-fix-paragraph (p1 p2)
  (goto-char p1)
  (let ((refill-start)
	(refill-stop))
    (when (re-search-forward "<br>$" p2 t)
      (goto-char p1)
      (when (re-search-forward ".+[^<][^b][^r][^>]$" p2 t)
	(beginning-of-line)
	(setq refill-start (point))
	(goto-char p2)
	(re-search-backward ".+[^<][^b][^r][^>]$" refill-start t)
	(forward-line 1)
	(end-of-line)
	;; refill-stop should ideally be adjusted to
	;; accommodate the "<br>" strings which are removed
	;; between refill-start and refill-stop.  Can simply
	;; be returned from my-replace-string
	(setq refill-stop (+ (point)
			     (html2text-replace-string
			      "<br>" ""
			      refill-start (point))))
	;; (message "Point = %s  refill-stop = %s" (point) refill-stop)
	;; (sleep-for 4)
	(fill-region refill-start refill-stop))))
  (html2text-replace-string "<br>" "" p1 p2))

;;
;; This one is interactive ...
;;
(defun html2text-fix-paragraphs ()
  "This _tries_ to fix up the paragraphs - this is done in quite a ad-hook
fashion, quite close to pure guess-work. It does work in some cases though."
  (interactive)
  (goto-char (point-min))
  (while (re-search-forward "^<br>$" nil t)
    (delete-region (match-beginning 0) (match-end 0)))
  ;; Removing lonely <br> on a single line, if they are left intact we
  ;; don't have any paragraphs at all.
  (goto-char (point-min))
  (while (not (eobp))
    (let ((p1 (point)))
      (forward-paragraph 1)
      ;;(message "Kaller fix med p1=%s  p2=%s " p1 (1- (point))) (sleep-for 5)
      (html2text-fix-paragraph p1 (1- (point)))
      (goto-char p1)
      (when (not (eobp))
	(forward-paragraph 1)))))

;;
;; </Functions to be called to fix up paragraphs>
;;

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;;
;; <Interactive functions>
;;

(defun html2text-remove-tags (tag-list)
  "Removes the tags listed in the list `html2text-remove-tag-list'.
See the documentation for that variable."
  (interactive)
  (dolist (tag tag-list)
    (goto-char (point-min))
    (while (re-search-forward (format "\\(</?%s[^>]*>\\)" tag) (point-max) t)
      (delete-region (match-beginning 0) (match-end 0)))))

(defun html2text-format-tags ()
  "See the variable `html2text-format-tag-list' for documentation."
  (interactive)
  (dolist (tag-and-function html2text-format-tag-list)
    (let ((tag      (car tag-and-function))
	  (function (cdr tag-and-function)))
      (goto-char (point-min))
      (while (re-search-forward (format "\\(<%s\\( [^>]*\\)?>\\)" tag)
				(point-max) t)
	(let ((p1)
	      (p2 (point))
	      (p3) (p4))
	  (search-backward "<" (point-min) t)
	  (setq p1 (point))
	  (unless (search-forward (format "</%s>" tag) (point-max) t)
	    (goto-char p2)
	    (insert (format "</%s>" tag)))
	  (setq p4 (point))
	  (search-backward "</" (point-min) t)
	  (setq p3 (point))
	  (funcall function p1 p2 p3 p4)
	  (goto-char p1))))))

(defun html2text-substitute ()
  "See the variable `html2text-replace-list' for documentation."
  (interactive)
  (dolist (e html2text-replace-list)
    (goto-char (point-min))
    (let ((old-string (car e))
	  (new-string (cdr e)))
      (html2text-replace-string old-string new-string (point-min) (point-max)))))

(defun html2text-format-single-elements ()
  (interactive)
  (dolist (tag-and-function html2text-format-single-element-list)
    (let ((tag      (car tag-and-function))
	  (function (cdr tag-and-function)))
      (goto-char (point-min))
      (while (re-search-forward (format "\\(<%s\\( [^>]*\\)?>\\)" tag)
				(point-max) t)
	(let ((p1)
	      (p2 (point)))
	  (search-backward "<" (point-min) t)
	  (setq p1 (point))
	  (funcall function p1 p2))))))

;;
;; Main function
;;

;;;###autoload
(defun html2text ()
  "Convert HTML to plain text in the current buffer."
  (interactive)
  (save-excursion
    (let ((case-fold-search t)
	  (buffer-read-only))
      (html2text-remove-tags html2text-remove-tag-list)
      (html2text-format-tags)
      (html2text-remove-tags html2text-remove-tag-list2)
      (html2text-substitute)
      (html2text-format-single-elements)
      (html2text-fix-paragraphs))))

;;
;; </Interactive functions>
;;
(provide 'html2text)

;;; html2text.el ends here