@wiris/mathtype-html-integration-devkit/src/latex.js

Allows to integrate MathType Web into any JavaScript HTML WYSIWYG rich text editor.

import TextCache from "./textcache";
import MathML from "./mathml";
import ServiceProvider from "./serviceprovider";
import Constants from "./constants";
import Util from "./util";

/**
 * @classdesc
 * This class represents a LaTeX parser. Manages the services which allows to convert
 * LaTeX into MathML and MathML into LaTeX.
 */
export default class Latex {
  /**
   * Static property.
   * Return latex cache.
   * @private
   * @type {Cache}
   */
  static get cache() {
    return Latex._cache;
  }

  /**
   * Static property setter.
   * Set latex cache.
   * @param {Cache} value - The property value.
   * @ignore
   */
  static set cache(value) {
    Latex._cache = value;
  }

  /**
   * Converts MathML to LaTeX by calling mathml2latex service. For text services
   * we call a text service with the param mathml2latex.
   * @param {String} mathml - MathML String.
   * @return {String} LaTeX string generated by the MathML argument.
   */
  static getLatexFromMathML(mathml) {
    const mathmlWithoutSemantics = MathML.removeSemantics(mathml);
    /**
     * @type {TextCache}
     */
    const { cache } = Latex;

    const data = {
      service: "mathml2latex",
      mml: mathmlWithoutSemantics,
    };

    const jsonResponse = JSON.parse(ServiceProvider.getService("service", data));

    // TODO: Error handling.
    let latex = "";

    if (jsonResponse.status === "ok") {
      latex = jsonResponse.result.text;
      const latexHtmlEntitiesEncoded = Util.htmlEntities(latex);
      // Inserting LaTeX semantics.
      const mathmlWithSemantics = MathML.addAnnotation(mathml, latexHtmlEntitiesEncoded, "LaTeX");
      cache.populate(latex, mathmlWithSemantics);
    }

    return latex;
  }

  /**
   * Converts LaTeX to MathML by calling latex2mathml service. For text services
   * we call a text service with the param latex2mathml.
   * @param {String} latex - String containing a LaTeX formula.
   * @param {Boolean} includeLatexOnSemantics
   * - If true LaTeX would me included into MathML semantics.
   * @return {String} MathML string generated by the LaTeX argument.
   */
  static getMathMLFromLatex(latex, includeLatexOnSemantics) {
    /**
     * @type {TextCache}
     */
    const latexCache = Latex.cache;

    if (Latex.cache.get(latex)) {
      return Latex.cache.get(latex);
    }
    const data = {
      service: "latex2mathml",
      latex,
    };

    if (includeLatexOnSemantics) {
      data.saveLatex = "";
    }

    const jsonResponse = JSON.parse(ServiceProvider.getService("service", data));

    let output;
    if (jsonResponse.status === "ok") {
      let mathml = jsonResponse.result.text;
      mathml = mathml.split("\r").join("").split("\n").join(" ");

      // Populate LatexCache.
      if (mathml.indexOf("semantics") === -1 && mathml.indexOf("annotation") === -1) {
        const content = Util.htmlEntities(latex);
        mathml = MathML.addAnnotation(mathml, content, "LaTeX");
        output = mathml;
      } else {
        output = mathml;
      }
      if (!latexCache.get(latex)) {
        latexCache.populate(latex, mathml);
      }
    } else {
      output = `$$${latex}$$`;
    }
    return output;
  }

  /**
   * Converts all occurrences of MathML code to LaTeX.
   * The MathML code should containing <annotation encoding="LaTeX"/> to be converted.
   * @param {String} content - A string containing MathML valid code.
   * @param {Object} characters - An object containing special characters.
   * @return {String} A string containing all MathML annotated occurrences
   * replaced by the corresponding LaTeX code.
   */
  static parseMathmlToLatex(content, characters) {
    let output = "";
    const mathTagBegin = `${characters.tagOpener}math`;
    const mathTagEnd = `${characters.tagOpener}/math${characters.tagCloser}`;
    const openTarget = `${characters.tagOpener}annotation encoding=${characters.doubleQuote}LaTeX${characters.doubleQuote}${characters.tagCloser}`;
    const closeTarget = `${characters.tagOpener}/annotation${characters.tagCloser}`;
    let start = content.indexOf(mathTagBegin);
    let end = 0;
    let mathml;
    let startAnnotation;
    let closeAnnotation;

    while (start !== -1) {
      output += content.substring(end, start);
      end = content.indexOf(mathTagEnd, start);

      if (end === -1) {
        end = content.length - 1;
      } else {
        end += mathTagEnd.length;
      }

      mathml = content.substring(start, end);

      startAnnotation = mathml.indexOf(openTarget);
      if (startAnnotation !== -1) {
        startAnnotation += openTarget.length;
        closeAnnotation = mathml.indexOf(closeTarget);
        let latex = mathml.substring(startAnnotation, closeAnnotation);
        if (characters === Constants.safeXmlCharacters) {
          latex = MathML.safeXmlDecode(latex);
        }
        output += `$$${latex}$$`;
        // Populate latex into cache.

        Latex.cache.populate(latex, mathml);
      } else {
        output += mathml;
      }
      start = content.indexOf(mathTagBegin, end);
    }

    output += content.substring(end, content.length);
    return output;
  }

  /**
   * Extracts the latex of a determined position in a text.
   * @param {Node} textNode - textNode to extract the LaTeX
   * @param {Number} caretPosition - Starting position to find LaTeX.
   * @param {Object} latexTags - Optional parameter representing tags between latex is inserted.
   * It has the 'open' attribute for the open tag and the 'close' attribute for the close tag.
   * "$$" by default.
   * @return {Object} An object with 3 keys: 'latex', 'start' and 'end'. Null if latex is not found.
   * @static
   */
  static getLatexFromTextNode(textNode, caretPosition, latexTags) {
    // TODO: Set LaTeX Tags as Core variable. Fix the call to this function (third argument).
    // Tags used for LaTeX formulas.
    const defaultLatexTags = {
      open: "$$",
      close: "$$",
    };
    // latexTags is an optional parameter. If is not set, use default latexTags.
    if (typeof latexTags === "undefined" || latexTags == null) {
      latexTags = defaultLatexTags;
    }
    // Looking for the first textNode.
    let startNode = textNode;

    while (startNode.previousSibling && startNode.previousSibling.nodeType === 3) {
      // TEXT_NODE.
      startNode = startNode.previousSibling;
    }

    /**
     * Returns the next latex position and node from a specific node and position.
     * @param {Node} currentNode - Node where searching latex.
     * @param {Number} currentPosition - Current position inside the currentNode.
     * @param {Object} latexTagsToUse - Tags used at latex beginning and latex final.
     * "$$" by default.
     * @param {Boolean} tag - Tag containing the current search.
     * @returns {Object} Object containing the current node and the position.
     */
    function getNextLatexPosition(currentNode, currentPosition, tag) {
      let position = currentNode.nodeValue.indexOf(tag, currentPosition);

      while (position === -1) {
        currentNode = currentNode.nextSibling;

        if (!currentNode) {
          // TEXT_NODE.
          return null; // Not found.
        }

        position = currentNode.nodeValue ? currentNode.nodeValue.indexOf(latexTags.close) : -1;
      }

      return {
        node: currentNode,
        position,
      };
    }

    /**
     * Determines if a node is previous, or not, to a second one.
     * @param {Node} node - Start node.
     * @param {Number} position - Start node position.
     * @param {Node} endNode - End node.
     * @param {Number} endPosition - End node position.
     * @returns {Boolean} True if the starting node is previous thant the en node. false otherwise.
     */
    function isPrevious(node, position, endNode, endPosition) {
      if (node === endNode) {
        return position <= endPosition;
      }
      while (node && node !== endNode) {
        node = node.nextSibling;
      }

      return node === endNode;
    }

    let start;
    let end = {
      node: startNode,
      position: 0,
    };
    // Is supposed that open and close tags has the same length.
    const tagLength = latexTags.open.length;
    do {
      start = getNextLatexPosition(end.node, end.position, latexTags.open);

      if (start == null || isPrevious(textNode, caretPosition, start.node, start.position)) {
        return null;
      }

      end = getNextLatexPosition(start.node, start.position + tagLength, latexTags.close);

      if (end == null) {
        return null;
      }

      end.position += tagLength;
    } while (isPrevious(end.node, end.position, textNode, caretPosition));

    // Isolating latex.
    let latex;

    if (start.node === end.node) {
      latex = start.node.nodeValue.substring(start.position + tagLength, end.position - tagLength);
    } else {
      const index = start.position + tagLength;
      latex = start.node.nodeValue.substring(index, start.node.nodeValue.length);
      let currentNode = start.node;

      do {
        currentNode = currentNode.nextSibling;
        if (currentNode === end.node) {
          latex += end.node.nodeValue.substring(0, end.position - tagLength);
        } else {
          latex += currentNode.nodeValue ? currentNode.nodeValue : "";
        }
      } while (currentNode !== end.node);
    }

    return {
      latex,
      startNode: start.node,
      startPosition: start.position,
      endNode: end.node,
      endPosition: end.position,
    };
  }
}

/**
 * Text cache. Stores all processed LaTeX strings and it's correspondent MathML string.
 * @type {Cache}
 * @static
 */
Latex._cache = new TextCache();