LibreChat/client/src/utils/latex.ts

// Regex to check if the processed content contains any potential LaTeX patterns
const containsLatexRegex =
  /\\\(.*?\\\)|\\\[.*?\\\]|\$.*?\$|\\begin\{equation\}.*?\\end\{equation\}/;

// Regex for inline and block LaTeX expressions
const inlineLatex = new RegExp(/\\\((.+?)\\\)/, 'g');
const blockLatex = new RegExp(/\\\[(.*?[^\\])\\\]/, 'gs');

// Function to restore code blocks
const restoreCodeBlocks = (content: string, codeBlocks: string[]) => {
  return content.replace(/<<CODE_BLOCK_(\d+)>>/g, (match, index) => codeBlocks[index]);
};

// Regex to identify code blocks and inline code
const codeBlockRegex = /(```[\s\S]*?```|`.*?`)/g;

export const processLaTeX = (_content: string) => {
  let content = _content;
  // Temporarily replace code blocks and inline code with placeholders
  const codeBlocks: string[] = [];
  let index = 0;
  content = content.replace(codeBlockRegex, (match) => {
    codeBlocks[index] = match;
    return `<<CODE_BLOCK_${index++}>>`;
  });

  // Escape dollar signs followed by a digit or space and digit
  let processedContent = content.replace(/(\$)(?=\s?\d)/g, '\\$');

  // If no LaTeX patterns are found, restore code blocks and return the processed content
  if (!containsLatexRegex.test(processedContent)) {
    return restoreCodeBlocks(processedContent, codeBlocks);
  }

  // Convert LaTeX expressions to a markdown compatible format
  processedContent = processedContent
    .replace(inlineLatex, (match: string, equation: string) => `$${equation}$`) // Convert inline LaTeX
    .replace(blockLatex, (match: string, equation: string) => `$$${equation}$$`); // Convert block LaTeX

  // Restore code blocks
  return restoreCodeBlocks(processedContent, codeBlocks);
};

/**
 * Preprocesses LaTeX content by replacing delimiters and escaping certain characters.
 *
 * @param content The input string containing LaTeX expressions.
 * @returns The processed string with replaced delimiters and escaped characters.
 */
export function preprocessLaTeX(content: string): string {
  // Step 1: Protect code blocks
  const codeBlocks: string[] = [];
  content = content.replace(/(```[\s\S]*?```|`[^`\n]+`)/g, (match, code) => {
    codeBlocks.push(code);
    return `<<CODE_BLOCK_${codeBlocks.length - 1}>>`;
  });

  // Step 2: Protect existing LaTeX expressions
  const latexExpressions: string[] = [];
  content = content.replace(/(\$\$[\s\S]*?\$\$|\\\[[\s\S]*?\\\]|\\\(.*?\\\))/g, (match) => {
    latexExpressions.push(match);
    return `<<LATEX_${latexExpressions.length - 1}>>`;
  });

  // Step 3: Escape dollar signs that are likely currency indicators
  content = content.replace(/\$(?=\d)/g, '\\$');

  // Step 4: Restore LaTeX expressions
  content = content.replace(/<<LATEX_(\d+)>>/g, (_, index) => latexExpressions[parseInt(index)]);

  // Step 5: Restore code blocks
  content = content.replace(/<<CODE_BLOCK_(\d+)>>/g, (_, index) => codeBlocks[parseInt(index)]);

  // Step 6: Apply additional escaping functions
  content = escapeBrackets(content);
  content = escapeMhchem(content);

  return content;
}

export function escapeBrackets(text: string): string {
  const pattern = /(```[\S\s]*?```|`.*?`)|\\\[([\S\s]*?[^\\])\\]|\\\((.*?)\\\)/g;
  return text.replace(
    pattern,
    (
      match: string,
      codeBlock: string | undefined,
      squareBracket: string | undefined,
      roundBracket: string | undefined,
    ): string => {
      if (codeBlock != null) {
        return codeBlock;
      } else if (squareBracket != null) {
        return `$$${squareBracket}$$`;
      } else if (roundBracket != null) {
        return `$${roundBracket}$`;
      }
      return match;
    },
  );
}

export function escapeMhchem(text: string) {
  return text.replaceAll('$\\ce{', '$\\\\ce{').replaceAll('$\\pu{', '$\\\\pu{');
}