@instructure/canvas-rce/es/rce/plugins/instructure_equation/EquationEditorModal/parseLatex.js

A component wrapping Canvas's usage of Tinymce

/*
 * Copyright (C) 2022 - present Instructure, Inc.
 *
 * This file is part of Canvas.
 *
 * Canvas is free software: you can redistribute it and/or modify it under
 * the terms of the GNU Affero General Public License as published by the Free
 * Software Foundation, version 3 of the License.
 *
 * Canvas 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 Affero General Public License for more
 * details.
 *
 * You should have received a copy of the GNU Affero General Public License along
 * with this program. If not, see <http://www.gnu.org/licenses/>.
 */

import { containsAdvancedSyntax } from './advancedOnlySyntax';
// Used to detect inline latex delimited like: \( ... \) OR $$ ... $$
const BOUNDARY_REGEX = /\\\((.+?)\\\)|\$\$(.+?)\$\$/g;
export const selectionIsLatex = selection => {
  return selection.startsWith('\\(') && selection.endsWith('\\)') || selection.startsWith('$$') && selection.endsWith('$$');
};
export const cleanLatex = latex => {
  const sansDelimiters = latex.substr(2, latex.length - 4);
  return sansDelimiters.replace(/&nbsp;/g, '').trim();
};
export const findLatex = (nodeValue, cursor) => {
  // The range could still contain more than one formulae, so we need to
  // isolate them and figure out which one the cursor is within.
  const latexMatches = nodeValue.match(BOUNDARY_REGEX);
  if (!latexMatches) return {};
  let leftIndex;
  let rightIndex;
  const foundLatex = latexMatches.find(latex => {
    leftIndex = nodeValue.indexOf(latex);
    rightIndex = leftIndex + latex.length;
    return leftIndex < cursor && cursor < rightIndex && selectionIsLatex(latex);
  });
  return foundLatex ? {
    latex: cleanLatex(foundLatex),
    leftIndex,
    rightIndex
  } : {};
};
export const parseLatex = editor => {
  const selection = editor.selection.getContent();
  const selectionNode = editor.selection.getNode();
  const editorRange = editor.selection.getRng();
  const startContainer = editorRange?.startContainer;
  const wholeText = startContainer?.wholeText;

  // check if selection is inline latex
  if (selection && selectionIsLatex(selection)) {
    const latex = cleanLatex(selection);
    return {
      latex,
      advancedOnly: containsAdvancedSyntax(latex)
    };
  } else if (selectionNode?.tagName === 'IMG' && selectionNode?.classList.contains('equation_image')) {
    // check if we launched modal from an equation image
    try {
      const src = new URL(selectionNode.src);
      const encodedLatex = src.pathname.replace(/^\/equation_images\//, '');
      const latex = decodeURIComponent(decodeURIComponent(encodedLatex));
      return {
        latex,
        advancedOnly: containsAdvancedSyntax(latex)
      };
    } catch (ex) {
      // probably failed to create the new URL
      return {};
    }
  } else if (wholeText) {
    // check if the cursor was within inline latex when launched

    // The `wholeText` value is not sufficient, since we could be dealing with
    // a number of nested ranges. The `nodeValue` is the text in the range in
    // which we have found the cursor.
    const nodeValue = startContainer.nodeValue || '';
    const cursor = editorRange.startOffset;
    const parsedLatex = findLatex(nodeValue, cursor);
    if (parsedLatex.latex) {
      parsedLatex.startContainer = startContainer;
      parsedLatex.advancedOnly = containsAdvancedSyntax(parsedLatex.latex);
    }
    return parsedLatex;
  } else {
    return {};
  }
};