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<?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/>.

/**
 * Moodle - Filter for converting TeX expressions to cached gif images
 *
 * This Moodle text filter converts TeX expressions delimited
 * by either $$...$$ or by <tex...>...</tex> tags to gif images using
 * mimetex.cgi obtained from http: *www.forkosh.com/mimetex.html authored by
 * John Forkosh john@forkosh.com.  Several binaries of this areincluded with
 * this distribution.
 * Note that there may be patent restrictions on the production of gif images
 * in Canada and some parts of Western Europe and Japan until July 2004.
 *
 * @package    filter
 * @subpackage tex
 * @copyright  2004 Zbigniew Fiedorowicz fiedorow@math.ohio-state.edu
 *             Originally based on code provided by Bruno Vernier bruno@vsbeducation.ca
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

defined('MOODLE_INTERNAL') || die;

require_once($CFG->libdir . '/classes/useragent.php');

/**
 * Create TeX image link.
 *
 * @param string $imagefile name of file
 * @param string $tex TeX notation (html entities already decoded)
 * @param int $height O means automatic
 * @param int $width O means automatic
 * @param string $align
 * @param string $alt
 * @return string HTML markup
 */
function filter_text_image($imagefile, $tex, $height, $width, $align, $alt) {
    global $CFG, $OUTPUT;

if (!$imagefile) {
        throw new coding_exception('image file argument empty in filter_text_image()');
    }

// Work out any necessary inline style.
    $rules = array();
    if ($align !== 'middle') {
        $rules[] = 'vertical-align:' . $align . ';';
    }
    if ($height) {
        $rules[] = 'height:' . $height . 'px;';
    }
    if ($width) {
        $rules[] = 'width:' . $width . 'px;';
    }
    if (!empty($rules)) {
        $style = ' style="' . implode('', $rules) . '" ';
    } else {
        $style = '';
    }

// Prepare the title attribute.
    // Note that we retain the title tag as TeX format rather than using
    // the alt text, even if supplied. The alt text is intended for blind
    // users (to provide a text equivalent to the equation) while the title
    // is there as a convenience for sighted users who want to see the TeX
    // code.
    $title = 'title="'.s($tex).'"';

if ($alt === '') {
        $alt = s($tex);
    } else {
        $alt = s(html_entity_decode($tex, ENT_QUOTES, 'UTF-8'));
    }

// Build the output.
    $anchorcontents = "<img class=\"texrender\" $title alt=\"$alt\" src=\"";
    if ($CFG->slasharguments) {        // Use this method if possible for better caching
        $anchorcontents .= "$CFG->wwwroot/filter/tex/pix.php/$imagefile";
    } else {
        $anchorcontents .= "$CFG->wwwroot/filter/tex/pix.php?file=$imagefile";
    }
    $anchorcontents .= "\" $style/>";

if (!file_exists("$CFG->dataroot/filter/tex/$imagefile") && has_capability('moodle/site:config', context_system::instance())) {
        $link = '/filter/tex/texdebug.php';
        $action = null;
    } else {
        $link = new moodle_url('/filter/tex/displaytex.php', array('texexp'=>$tex));
        $action = new popup_action('click', $link, 'popup', array('width'=>320,'height'=>240));
    }
    $output = $OUTPUT->action_link($link, $anchorcontents, $action, array('title'=>'TeX')); //TODO: the popups do not work when text caching is enabled!!
    $output = "<span class=\"MathJax_Preview\">$output</span><script type=\"math/tex\">$tex</script>";

return $output;
}

/**
 * TeX filtering class.
 */
class filter_tex extends moodle_text_filter {
    function filter($text, array $options = array()) {

global $CFG, $DB;

/// Do a quick check using stripos to avoid unnecessary work
        if ((!preg_match('/<tex/i', $text)) &&
                (strpos($text,'$$') === false) &&
                (strpos($text,'\\[') === false) &&
                (strpos($text, '\\(') === false) &&
                (!preg_match('/\[tex/i',$text))) {
            return $text;
        }

#    //restrict filtering to forum 130 (Maths Tools on moodle.org)
#    $scriptname = $_SERVER['SCRIPT_NAME'];
#    if (!strstr($scriptname,'/forum/')) {
#        return $text;
#    }
#    if (strstr($scriptname,'post.php')) {
#        $parent = forum_get_post_full($_GET['reply']);
#        $discussion = $DB->get_record("forum_discussions", array("id"=>$parent->discussion));
#    } else if (strstr($scriptname,'discuss.php')) {
#        $discussion = $DB->get_record("forum_discussions", array("id"=>$_GET['d']));
#    } else {
#        return $text;
#    }
#    if ($discussion->forum != 130) {
#        return $text;
#    }
        $text .= ' ';
        preg_match_all('/\$(\$\$+?)([^\$])/s',$text,$matches);
        for ($i=0; $i<count($matches[0]); $i++) {
            $replacement = str_replace('$','$', $matches[1][$i]).$matches[2][$i];
            $text = str_replace($matches[0][$i], $replacement, $text);
        }

// <tex> TeX expression </tex>
        // or <tex alt="My alternative text to be used instead of the TeX form"> TeX expression </tex>
        // or $$ TeX expression $$
        // or \[ TeX expression \]          // original tag of MathType and TeXaide (dlnsk)
        // or [tex] TeX expression [/tex]   // somtime it's more comfortable than <tex> (dlnsk)
        $rules = array(
            '<tex(?:\s+alt=["\'](.*?)["\'])?>(.+?)<\/tex>',
            '\$\$(.+?)\$\$',
            '\\\\\[(.+?)\\\\\]',
            '\\\\$(.+?)\\\\$',
            '\\[tex\\](.+?)\\[\/tex\\]'
        );
        $megarule = '/' . implode($rules, '|') . '/is';
        preg_match_all($megarule, $text, $matches);
        for ($i=0; $i<count($matches[0]); $i++) {
            $texexp = '';
            for ($j = 0; $j < count($rules); $j++) {
                $texexp .= $matches[$j + 2][$i];
            }
            $alt = $matches[1][$i];
            $texexp = str_replace('<nolink>','',$texexp);
            $texexp = str_replace('</nolink>','',$texexp);
            $texexp = str_replace('<span class="nolink">','',$texexp);
            $texexp = str_replace('</span>','',$texexp);
            $texexp = preg_replace("/<br[[:space:]]*\/?>/i", '', $texexp);  //dlnsk
            $align = "middle";
            if (preg_match('/^align=bottom /',$texexp)) {
              $align = "text-bottom";
              $texexp = preg_replace('/^align=bottom /','',$texexp);
            } else if (preg_match('/^align=top /',$texexp)) {
              $align = "text-top";
              $texexp = preg_replace('/^align=top /','',$texexp);
            }

// decode entities encoded by editor, luckily there is very little chance of double decoding
            $texexp = html_entity_decode($texexp, ENT_QUOTES, 'UTF-8');

if ($texexp === '') {
                continue;
            }

$md5 = md5($texexp);
            if (!$DB->record_exists("cache_filters", array("filter"=>"tex", "md5key"=>$md5))) {
                $texcache = new stdClass();
                $texcache->filter = 'tex';
                $texcache->version = 1;
                $texcache->md5key = $md5;
                $texcache->rawtext = $texexp;
                $texcache->timemodified = time();
                $DB->insert_record("cache_filters", $texcache, false);
            }
            $convertformat = get_config('filter_tex', 'convertformat');
            if ($convertformat == 'svg' && !core_useragent::supports_svg()) {
                $convertformat = 'png';
            }
            $filename = $md5.".{$convertformat}";
            $text = str_replace( $matches[0][$i], filter_text_image($filename, $texexp, 0, 0, $align, $alt), $text);
        }
        return $text;
    }
}