<?php
/**
 * LaTeX Rendering Class
 * Copyright (C) 2003  Benjamin Zeiss <zeiss@math.uni-goettingen.de>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 * --------------------------------------------------------------------
 * @author Benjamin Zeiss <zeiss@math.uni-goettingen.de>
 * @version v0.8
 * @package latexrender
 *
 */

class LatexRender {

    // ====================================================================================
    // Variable Definitions
    // ====================================================================================
    var $_picture_path = "";
    var $_picture_path_httpd = "";
    var $_tmp_dir = "";
    // i was too lazy to write mutator functions for every single program used
    // just access it outside the class or change it here if nescessary
    var $_latex_path = "/usr/bin/latex";
    var $_dvips_path = "/usr/bin/dvips";
    var $_convert_path = "/usr/bin/convert";
    var $_identify_path="/usr/bin/identify";
    var $_formula_density = 120;  
    var $_xsize_limit = 1000;
    var $_ysize_limit = 1000;
    var $_string_length_limit = 4096;
	var $_font_size = 12;
	var $_latexclass = "article"; //install extarticle class if you wish to have smaller font sizes
    var $_tmp_filename;
	var $_image_format = "png"; //change to png if you prefer
    // this most certainly needs to be extended. in the long term it is planned to use
    // a positive list for more security. this is hopefully enough for now. i'd be glad
    // to receive more bad tags !
    var $_latex_tags_blacklist = array(
        "include","def","command","loop","repeat","open","toks","output","input",
        "catcode","name","^^","usepackage",
        "\\every","\\errhelp","\\errorstopmode","\\scrollmode","\\nonstopmode","\\batchmode",
        "\\read","\\write","csname","\\newhelp","\\uppercase", "\\lowercase","\\relax","\\aftergroup",
        "\\afterassignment","\\expandafter","\\noexpand","\\special"
        );
    var $_errorcode = 0;
	var $_errorextra = "";


    // ====================================================================================
    // constructor
    // ====================================================================================

    /**
     * Initializes the class
     *
     * @param string path where the rendered pictures should be stored
     * @param string same path, but from the httpd chroot
     */
    function LatexRender($picture_path,$picture_path_httpd,$tmp_dir) {
        $this->_picture_path = $picture_path;
        $this->_picture_path_httpd = $picture_path_httpd;
        $this->_tmp_dir = $tmp_dir;
        $this->_tmp_filename = md5(rand());
    }

    // ====================================================================================
    // public functions
    // ====================================================================================

    /**
     * Picture path Mutator function
     *
     * @param string sets the current picture path to a new location
     */
    function setPicturePath($name) {
        $this->_picture_path = $name;
    }

    /**
     * Picture path Mutator function
     *
     * @returns the current picture path
     */
    function getPicturePath() {
        return $this->_picture_path;
    }

    /**
     * Picture path HTTPD Mutator function
     *
     * @param string sets the current httpd picture path to a new location
     */
    function setPicturePathHTTPD($name) {
        $this->_picture_path_httpd = $name;
    }

    /**
     * Picture path HTTPD Mutator function
     *
     * @returns the current picture path
     */
    function getPicturePathHTTPD() {
        return $this->_picture_path_httpd;
    }

    /**
     * Tries to match the LaTeX Formula given as argument against the
     * formula cache. If the picture has not been rendered before, it'll
     * try to render the formula and drop it in the picture cache directory.
     *
     * @param string formula in LaTeX format
     * @returns the webserver based URL to a picture which contains the
     * requested LaTeX formula. If anything fails, the resultvalue is false.
     */
    function getFormulaURL($latex_formula) {
        // circumvent certain security functions of web-software which
        // is pretty pointless right here
        $latex_formula = preg_replace("/&gt;/i", ">", $latex_formula);
        $latex_formula = preg_replace("/&lt;/i", "<", $latex_formula);

        $formula_hash = md5($latex_formula . ";fd=" . $this->_formula_density);

        $filename = $formula_hash.".".$this->_image_format;
        $full_path_filename = $this->getPicturePath()."/".$filename;

        if (is_file($full_path_filename)) {
            return $this->getPicturePathHTTPD()."/".$filename;
        } else {
            // security filter: reject too long formulas
            if (strlen($latex_formula) > $this->_string_length_limit) {
            	$this->_errorcode = 1;
                return false;
            }

            // security filter: try to match against LaTeX-Tags Blacklist
            for ($i=0;$i<sizeof($this->_latex_tags_blacklist);$i++) {
                if (stristr($latex_formula,$this->_latex_tags_blacklist[$i])) {
                	$this->_errorcode = 2;
                    return false;
                }
            }

            // security checks assume correct formula, let's render it
            if ($this->renderLatex($latex_formula)) {
                return $this->getPicturePathHTTPD()."/".$filename;
            } else {
                // uncomment if required
                // $this->_errorcode = 3;
                return false;
            }
        }
    }

    // ====================================================================================
    // private functions
    // ====================================================================================

    /**
     * wraps a minimalistic LaTeX document around the formula and returns a string
     * containing the whole document as string. Customize if you want other fonts for
     * example.
     *
     * @param string formula in LaTeX format
     * @returns minimalistic LaTeX document containing the given formula
     */
    function wrap_formula($latex_formula) {
        $string  = "\documentclass[".$this->_font_size."pt]{".$this->_latexclass."}\n";
        $string .= "\usepackage[latin1]{inputenc}\n";
        $string .= "\usepackage{amsmath}\n";
        $string .= "\usepackage{amsfonts}\n";
        $string .= "\usepackage{amssymb}\n";
        $string .= "\pagestyle{empty}\n";
        $string .= "\begin{document}\n";
        $string .= "$".$latex_formula."$\n";
        $string .= "\end{document}\n";

        return $string;
    }

    /**
     * returns the dimensions of a picture file using 'identify' of the
     * imagemagick tools. The resulting array can be adressed with either
     * $dim[0] / $dim[1] or $dim["x"] / $dim["y"]
     *
     * @param string path to a picture
     * @returns array containing the picture dimensions
     */
    function getDimensions($filename) {
        $output=exec($this->_identify_path." ".$filename);
        $result=explode(" ",$output);
        $dim=explode("x",$result[2]);
        $dim["x"] = $dim[0];
        $dim["y"] = $dim[1];

        return $dim;
    }

    /**
     * Renders a LaTeX formula by the using the following method:
     *  - write the formula into a wrapped tex-file in a temporary directory
     *    and change to it
     *  - Create a DVI file using latex (tetex)
     *  - Convert DVI file to Postscript (PS) using dvips (tetex)
     *  - convert, trim and add transparancy by using 'convert' from the
     *    imagemagick package.
     *  - Save the resulting image to the picture cache directory using an
     *    md5 hash as filename. Already rendered formulas can be found directly
     *    this way.
     *
     * @param string LaTeX formula
     * @returns true if the picture has been successfully saved to the picture
     *          cache directory
     */
    function renderLatex($latex_formula) {
        $latex_document = $this->wrap_formula($latex_formula);

        $current_dir = getcwd();

        chdir($this->_tmp_dir);

        // create temporary latex file
        $fp = fopen($this->_tmp_dir."/".$this->_tmp_filename.".tex","a+");
        fputs($fp,$latex_document);
        fclose($fp);

        // create temporary dvi file
        $command = $this->_latex_path." --interaction=nonstopmode ".$this->_tmp_filename.".tex";
        $status_code = exec($command);

        if (!$status_code) { $this->cleanTemporaryDirectory(); chdir($current_dir); $this->_errorcode = 4; return false; }

        // convert dvi file to postscript using dvips
        $command = $this->_dvips_path." -E ".$this->_tmp_filename.".dvi"." -o ".$this->_tmp_filename.".ps";
        $status_code = exec($command);

        // imagemagick convert ps to image and trim picture
        $command = $this->_convert_path." -density ".$this->_formula_density.
                    " -trim -transparent \"#FFFFFF\" ".$this->_tmp_filename.".ps ".
                    $this->_tmp_filename.".".$this->_image_format;

        $status_code = exec($command);

        // test picture for correct dimensions
        $dim = $this->getDimensions($this->_tmp_filename.".".$this->_image_format);

        if ( ($dim["x"] > $this->_xsize_limit) or ($dim["y"] > $this->_ysize_limit)) {
            $this->cleanTemporaryDirectory();
            chdir($current_dir);
            $this->_errorcode = 5;
            $this->_errorextra = ": " . $dim["x"] . "x" . number_format($dim["y"],0,"","");
            return false;
        }

        // copy temporary formula file to cahed formula directory
        $latex_hash = md5($latex_formula . ";fd=" . $this->_formula_density);
        $filename = $this->getPicturePath()."/".$latex_hash.".".$this->_image_format;

        $status_code = copy($this->_tmp_filename.".".$this->_image_format,$filename);

        $this->cleanTemporaryDirectory();

        if (!$status_code) { chdir($current_dir); $this->_errorcode = 6; return false; }
        chdir($current_dir);

        return true;
    }

    /**
     * Cleans the temporary directory
     */
    function cleanTemporaryDirectory() {
        $current_dir = getcwd();
        chdir($this->_tmp_dir);

        unlink($this->_tmp_dir."/".$this->_tmp_filename.".tex");
        unlink($this->_tmp_dir."/".$this->_tmp_filename.".aux");
        unlink($this->_tmp_dir."/".$this->_tmp_filename.".log");
        unlink($this->_tmp_dir."/".$this->_tmp_filename.".dvi");
        unlink($this->_tmp_dir."/".$this->_tmp_filename.".ps");
        unlink($this->_tmp_dir."/".$this->_tmp_filename.".".$this->_image_format);

        chdir($current_dir);
    }

}
