html2text.php

<?php

// This file is part of Moodle - http://moodle.org/
//
// Moodle 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.
//
// Moodle 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 Moodle.  If not, see <http://www.gnu.org/licenses/>.
//
// Author(s): Jon Abernathy <jon@chuggnutt.com>
// Copyright (c) 2005-2007 Jon Abernathy <jon@chuggnutt.com>

/**
 *  Takes HTML and converts it to formatted, plain text.
 *
 *  Thanks to Alexander Krug (http://www.krugar.de/) to pointing out and
 *  correcting an error in the regexp search array. Fixed 7/30/03.
 *
 *  Updated set_html() function's file reading mechanism, 9/25/03.
 *
 *  Thanks to Joss Sanglier (http://www.dancingbear.co.uk/) for adding
 *  several more HTML entity codes to the $search and $replace arrays.
 *  Updated 11/7/03.
 *
 *  Thanks to Darius Kasperavicius (http://www.dar.dar.lt/) for
 *  suggesting the addition of $allowed_tags and its supporting function
 *  (which I slightly modified). Updated 3/12/04.
 *
 *  Thanks to Justin Dearing for pointing out that a replacement for the
 *  <TH> tag was missing, and suggesting an appropriate fix.
 *  Updated 8/25/04.
 *
 *  Thanks to Mathieu Collas (http://www.myefarm.com/) for finding a
 *  display/formatting bug in the _build_link_list() function: email
 *  readers would show the left bracket and number ("[1") as part of the
 *  rendered email address.
 *  Updated 12/16/04.
 *
 *  Thanks to Wojciech Bajon (http://histeria.pl/) for submitting code
 *  to handle relative links, which I hadn't considered. I modified his
 *  code a bit to handle normal HTTP links and MAILTO links. Also for
 *  suggesting three additional HTML entity codes to search for.
 *  Updated 03/02/05.
 *
 *  Thanks to Jacob Chandler for pointing out another link condition
 *  for the _build_link_list() function: "https".
 *  Updated 04/06/05.
 *
 *  Thanks to Marc Bertrand (http://www.dresdensky.com/) for
 *  suggesting a revision to the word wrapping functionality; if you
 *  specify a $width of 0 or less, word wrapping will be ignored.
 *  Updated 11/02/06.
 *
 *  *** Big housecleaning updates below:
 *
 *  Thanks to Colin Brown (http://www.sparkdriver.co.uk/) for
 *  suggesting the fix to handle </li> and blank lines (whitespace).
 *  Christian Basedau (http://www.movetheweb.de/) also suggested the
 *  blank lines fix.
 *
 *  Special thanks to Marcus Bointon (http://www.synchromedia.co.uk/),
 *  Christian Basedau, Norbert Laposa (http://ln5.co.uk/),
 *  Bas van de Weijer, and Marijn van Butselaar
 *  for pointing out my glaring error in the <th> handling. Marcus also
 *  supplied a host of fixes.
 *
 *  Thanks to Jeffrey Silverman (http://www.newtnotes.com/) for pointing
 *  out that extra spaces should be compressed--a problem addressed with
 *  Marcus Bointon's fixes but that I had not yet incorporated.
 *
 *	Thanks to Daniel Schledermann (http://www.typoconsult.dk/) for
 *  suggesting a valuable fix with <a> tag handling.
 *
 *  Thanks to Wojciech Bajon (again!) for suggesting fixes and additions,
 *  including the <a> tag handling that Daniel Schledermann pointed
 *  out but that I had not yet incorporated. I haven't (yet)
 *  incorporated all of Wojciech's changes, though I may at some
 *  future time.
 *
 *  *** End of the housecleaning updates. Updated 08/08/07.
 *
 * @package   moodlecore
 * @copyright Jon Abernathy <jon@chuggnutt.com>
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

/**
 * @package   moodlecore
 * @copyright Jon Abernathy <jon@chuggnutt.com>
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
class html2text
{

    /**
     *  Contains the HTML content to convert.
     *
     *  @var string $html
     *  @access public
     */
    var $html;

    /**
     *  Contains the converted, formatted text.
     *
     *  @var string $text
     *  @access public
     */
    var $text;

    /**
     *  Maximum width of the formatted text, in columns.
     *
     *  Set this value to 0 (or less) to ignore word wrapping
     *  and not constrain text to a fixed-width column.
     *
     *  @var integer $width
     *  @access public
     */
    var $width = 70;

    /**
     *  List of preg* regular expression patterns to search for,
     *  used in conjunction with $replace.
     *
     *  @var array $search
     *  @access public
     *  @see $replace
     */
    var $search = array(
        "/\r/",                                  // Non-legal carriage return
        "/[\n\t]+/",                             // Newlines and tabs
        '/[ ]{2,}/',                             // Runs of spaces, pre-handling
        '/<script[^>]*>.*?<\/script>/i',         // <script>s -- which strip_tags supposedly has problems with
        '/<style[^>]*>.*?<\/style>/i',           // <style>s -- which strip_tags supposedly has problems with
        //'/<!-- .* -->/',                         // Comments -- which strip_tags might have problem a with
        '/<p[^>]*>/i',                           // <P>
        '/<br[^>]*>/i',                          // <br>
        '/<i[^>]*>(.*?)<\/i>/i',                 // <i>
        '/<em[^>]*>(.*?)<\/em>/i',               // <em>
        '/(<ul[^>]*>|<\/ul>)/i',                 // <ul> and </ul>
        '/(<ol[^>]*>|<\/ol>)/i',                 // <ol> and </ol>
        '/<li[^>]*>(.*?)<\/li>/i',               // <li> and </li>
        '/<li[^>]*>/i',                          // <li>
        '/<hr[^>]*>/i',                          // <hr>
        '/(<table[^>]*>|<\/table>)/i',           // <table> and </table>
        '/(<tr[^>]*>|<\/tr>)/i',                 // <tr> and </tr>
        '/<td[^>]*>(.*?)<\/td>/i',               // <td> and </td>
        '/&(nbsp|#160);/i',                      // Non-breaking space
        '/&(quot|rdquo|ldquo|#8220|#8221|#147|#148);/i',
		                                         // Double quotes
        '/&(apos|rsquo|lsquo|#8216|#8217);/i',   // Single quotes
        '/&gt;/i',                               // Greater-than
        '/&lt;/i',                               // Less-than
        '/&(amp|#38);/i',                        // Ampersand
        '/&(copy|#169);/i',                      // Copyright
        '/&(trade|#8482|#153);/i',               // Trademark
        '/&(reg|#174);/i',                       // Registered
        '/&(mdash|#151|#8212);/i',               // mdash
        '/&(ndash|minus|#8211|#8722);/i',        // ndash
        '/&(bull|#149|#8226);/i',                // Bullet
        '/&(pound|#163);/i',                     // Pound sign
        '/&(euro|#8364);/i',                     // Euro sign
        '/[ ]+([\n\t])/',                        // Trailing spaces before newline or tab
        '/[ ]{2,}/'                              // Runs of spaces, post-handling
    );

    /**
     *  List of pattern replacements corresponding to patterns searched.
     *
     *  @var array $replace
     *  @access public
     *  @see $search
     */
    var $replace = array(
        '',                                     // Non-legal carriage return
        ' ',                                    // Newlines and tabs
        ' ',                                    // Runs of spaces, pre-handling
        '',                                     // <script>s -- which strip_tags supposedly has problems with
        '',                                     // <style>s -- which strip_tags supposedly has problems with
        //'',                                     // Comments -- which strip_tags might have problem a with
        "\n\n",                               // <P>
        "\n",                                   // <br>
        '_\\1_',                                // <i>
        '_\\1_',                                // <em>
        "\n\n",                                 // <ul> and </ul>
        "\n\n",                                 // <ol> and </ol>
        "\t* \\1\n",                            // <li> and </li>
        "\n\t* ",                               // <li>
        "\n-------------------------\n",        // <hr>
        "\n\n",                                 // <table> and </table>
        "\n",                                   // <tr> and </tr>
        "\t\t\\1\n",                            // <td> and </td>
        ' ',                                    // Non-breaking space
        '"',                                    // Double quotes
        "'",                                    // Single quotes
        '>',
        '<',
        '&',
        '(c)',
        '(tm)',
        '(R)',
        '--',
        '-',
        '*',
        '£',
        'EUR',                                  // Euro sign. € ?
        '\\1',                                  // Trailing spaces before newline or tab
        ' '                                     // Runs of spaces, post-handling
    );

    /**
     *  List of preg* regular expression patterns to search for
     *  and replace using callback function.
     *
     *  @var array $callback_search
     *  @access public
     */
    var $callback_search = array(
        '/<(h)[123456][^>]*>(.*?)<\/h[123456]>/i', // H1 - H3
        '/<(b)[^>]*>(.*?)<\/b>/i',                 // <b>
        '/<(strong)[^>]*>(.*?)<\/strong>/i',       // <strong>
        '/<(a) [^>]*href=("|\')([^"\']+)\2[^>]*>(.*?)<\/a>/i',
                                                   // <a href="">
        '/<(th)[^>]*>(.*?)<\/th>/i',               // <th> and </th>
        '/<(img)[^>]*alt=\"([^>"]+)\"[^>]*>/i',    // <img> with alt
    );

   /**
    *  List of preg* regular expression patterns to search for in PRE body,
    *  used in conjunction with $pre_replace.
    *
    *  @var array $pre_search
    *  @access public
    *  @see $pre_replace
    */
    var $pre_search = array(
        "/\n/",
        "/\t/",
        '/ /',
        '/<pre[^>]*>/',
        '/<\/pre>/'
    );

    /**
     *  List of pattern replacements corresponding to patterns searched for PRE body.
     *
     *  @var array $pre_replace
     *  @access public
     *  @see $pre_search
     */
    var $pre_replace = array(
        '<br>',
        '&nbsp;&nbsp;&nbsp;&nbsp;',
        '&nbsp;',
        '',
        ''
    );

    /**
     *  Contains a list of HTML tags to allow in the resulting text.
     *
     *  @var string $allowed_tags
     *  @access public
     *  @see set_allowed_tags()
     */
    var $allowed_tags = '';

    /**
     *  Contains the base URL that relative links should resolve to.
     *
     *  @var string $url
     *  @access public
     */
    var $url;

    /**
     *  Indicates whether content in the $html variable has been converted yet.
     *
     *  @var boolean $_converted
     *  @access private
     *  @see $html, $text
     */
    var $_converted = false;

    /**
     *  Contains URL addresses from links to be rendered in plain text.
     *
     *  @var string $_link_list
     *  @access private
     *  @see _build_link_list()
     */
    var $_link_list = '';

    /**
     *  Number of valid links detected in the text, used for plain text
     *  display (rendered similar to footnotes).
     *
     *  @var integer $_link_count
     *  @access private
     *  @see _build_link_list()
     */
    var $_link_count = 0;

    /**
     * Boolean flag, true if a table of link URLs should be listed after the text.
     *
     * @var boolean $_do_links
     * @access private
     * @see html2text()
     */
    var $_do_links = true;

    /**
     *  Constructor.
     *
     *  If the HTML source string (or file) is supplied, the class
     *  will instantiate with that source propagated, all that has
     *  to be done it to call get_text().
     *
     *  @param string $source HTML content
     *  @param boolean $from_file Indicates $source is a file to pull content from
     *  @param boolean $do_links Indicate whether a table of link URLs is desired
     *  @param integer $width Maximum width of the formatted text, 0 for no limit
     *  @access public
     *  @return void
     */
    function html2text( $source = '', $from_file = false, $do_links = true, $width = 75 )
    {
        if ($source !== '') {
            $this->set_html($source, $from_file);
        }

        $this->set_base_url();
        $this->_do_links = $do_links;
        $this->width = $width;
    }

    /**
     *  Loads source HTML into memory, either from $source string or a file.
     *
     *  @param string $source HTML content
     *  @param boolean $from_file Indicates $source is a file to pull content from
     *  @access public
     *  @return void
     */
    function set_html( $source, $from_file = false )
    {
        if ( $from_file && file_exists($source) ) {
            $this->html = file_get_contents($source);
        }
        else
            $this->html = $source;

        $this->_converted = false;
    }

    /**
     *  Returns the text, converted from HTML.
     *
     *  @access public
     *  @return string
     */
    function get_text()
    {
        if ( !$this->_converted ) {
            $this->_convert();
        }

        return $this->text;
    }

    /**
     *  Prints the text, converted from HTML.
     *
     *  @access public
     *  @return void
     */
    function print_text()
    {
        print $this->get_text();
    }

    /**
     *  Alias to print_text(), operates identically.
     *
     *  @access public
     *  @return void
     *  @see print_text()
     */
    function p()
    {
        print $this->get_text();
    }

    /**
     *  Sets the allowed HTML tags to pass through to the resulting text.
     *
     *  Tags should be in the form "<p>", with no corresponding closing tag.
     *
     *  @access public
     *  @return void
     */
    function set_allowed_tags( $allowed_tags = '' )
    {
        if ( !empty($allowed_tags) ) {
            $this->allowed_tags = $allowed_tags;
        }
    }

    /**
     *  Sets a base URL to handle relative links.
     *
     *  @access public
     *  @return void
     */
    function set_base_url( $url = '' )
    {
        if ( empty($url) ) {
        	if ( !empty($_SERVER['HTTP_HOST']) ) {
	            $this->url = 'http://' . $_SERVER['HTTP_HOST'];
        	} else {
	            $this->url = '';
	        }
        } else {
            // Strip any trailing slashes for consistency (relative
            // URLs may already start with a slash like "/file.html")
            if ( substr($url, -1) == '/' ) {
                $url = substr($url, 0, -1);
            }
            $this->url = $url;
        }
    }

    /**
     *  Workhorse function that does actual conversion.
     *
     *  First performs custom tag replacement specified by $search and
     *  $replace arrays. Then strips any remaining HTML tags, reduces whitespace
     *  and newlines to a readable format, and word wraps the text to
     *  $width characters.
     *
     *  @access private
     *  @return void
     */
    function _convert()
    {
        // Variables used for building the link list
        $this->_link_count = 0;
        $this->_link_list = '';

        $text = trim($this->html);

        // Convert <PRE>
        $this->_convert_pre($text);

        // Run our defined search-and-replace
        $text = preg_replace($this->search, $this->replace, $text);
        $text = preg_replace_callback($this->callback_search, array('html2text', '_preg_callback'), $text);

        // Replace known html entities
        $text = html_entity_decode($text, ENT_COMPAT, 'UTF-8');

        // Remove unknown/unhandled entities (this cannot be done in search-and-replace block)
        $text = preg_replace('/&[^&;]+;/i', '', $text);

        // Strip any other HTML tags
        $text = strip_tags($text, $this->allowed_tags);

        // Bring down number of empty lines to 2 max
        $text = preg_replace("/\n\s+\n/", "\n\n", $text);
        $text = preg_replace("/[\n]{3,}/", "\n\n", $text);

        // Add link list
        if ( !empty($this->_link_list) ) {
            $text .= "\n\nLinks:\n------\n" . $this->_link_list;
        }

        // Wrap the text to a readable format
        // for PHP versions >= 4.0.2. Default width is 75
        // If width is 0 or less, don't wrap the text.
        if ( $this->width > 0 ) {
        	$text = wordwrap($text, $this->width);
        }

        $this->text = $text;

        $this->_converted = true;
    }

    /**
     *  Helper function called by preg_replace() on link replacement.
     *
     *  Maintains an internal list of links to be displayed at the end of the
     *  text, with numeric indices to the original point in the text they
     *  appeared. Also makes an effort at identifying and handling absolute
     *  and relative links.
     *
     *  @param string $link URL of the link
     *  @param string $display Part of the text to associate number with
     *  @access private
     *  @return string
     */
    function _build_link_list( $link, $display )
    {
	if ( !$this->_do_links ) return $display;

	if ( substr($link, 0, 7) == 'http://' || substr($link, 0, 8) == 'https://' ||
             substr($link, 0, 7) == 'mailto:' ) {
            $this->_link_count++;
            $this->_link_list .= "[" . $this->_link_count . "] $link\n";
            $additional = ' [' . $this->_link_count . ']';
	} elseif ( substr($link, 0, 11) == 'javascript:' ) {
		// Don't count the link; ignore it
		$additional = '';
		// what about href="#anchor" ?
        } else {
            $this->_link_count++;
            $this->_link_list .= "[" . $this->_link_count . "] " . $this->url;
            if ( substr($link, 0, 1) != '/' ) {
                $this->_link_list .= '/';
            }
            $this->_link_list .= "$link\n";
            $additional = ' [' . $this->_link_count . ']';
        }

        return $display . $additional;
    }

    /**
     *  Helper function for PRE body conversion.
     *
     *  @param string $text HTML content
     *  @access private
     */
    function _convert_pre(&$text)
    {
        while(preg_match('/<pre[^>]*>(.*)<\/pre>/ismU', $text, $matches)) {
            $result = preg_replace($this->pre_search, $this->pre_replace, $matches[1]);
            $text = preg_replace('/<pre[^>]*>.*<\/pre>/ismU', '<div><br>' . $result . '<br></div>', $text, 1);
        }
    }

    /**
     *  Callback function for preg_replace_callback use.
     *
     *  @param  array $matches PREG matches
     *  @return string
     *  @access private
     */
    function _preg_callback($matches)
    {
        switch($matches[1]) {
        case 'b':
        case 'strong':
            return $this->_strtoupper($matches[2]);
        case 'hr':
            return $this->_strtoupper("\t\t". $matches[2] ."\n");
        case 'h':
            return $this->_strtoupper("\n\n". $matches[2] ."\n\n");
        case 'a':
            return $this->_build_link_list($matches[3], $matches[4]);
        case 'img':
            return '[' . $matches[2] . ']';
        }
    }

    /**
     *  Strtoupper multibyte wrapper function
     *
     *  @param  string $str
     *  @return string
     *  @access private
     */
    function _strtoupper($str)
    {
        $tl = textlib_get_instance();
        return $tl->strtoupper($str);
    }
}