synctos/src/loading/file-fragment-loader.js

The Syncmaker. A tool to build comprehensive sync functions for Couchbase Sync Gateway.

/**
 * Replaces each instance of the specified macro in the given raw text with the contents of the referenced file fragment.
 *
 * @param {string} baseDir The base directory to use when attempting to read a file fragment as a relative path
 * @param {string} macroName The name of the macro to replace in the raw text
 * @param {string} rawText The raw content string in which to replace instances of the specified macro
 *
 * @returns A copy of the given text where each instance of the macro has been replaced with the contents of its corresponding file fragment
 */
exports.load = load;

const fs = require('fs');

function load(baseDir, macroName, rawText) {
  function replacer(fullMatch, fragmentFilename) {
    const rawFileContents = readFileFragment(fragmentFilename, baseDir);

    // Recursively replace macros nested an arbitrary number of levels deep. Recursion terminates when it encounters a
    // template file that does not contain the specified macro (i.e. this replacer will not run when `rawText.replace`
    // is called without an instance of the macro in the file contents).
    return load(baseDir, macroName, rawFileContents);
  }

  return rawText.replace(new RegExp(`\\b${macroName}\\s*\\(\\s*"((?:\\\\"|[^"])+)"\\s*\\)`, 'g'), replacer)
    .replace(new RegExp(`\\b${macroName}\\s*\\(\\s*'((?:\\\\'|[^'])+)'\\s*\\)`, 'g'), replacer);
}

function readFileFragment(fragmentFilename, baseDir) {
  // The filename may have been defined with escape sequences (e.g. \\, \', \") in it, so unescape them
  const sanitizedFragmentFilename = fragmentFilename.replace(/\\(.)/g, (escapeSequence, escapedChar) => escapedChar);

  try {
    // Attempt to import the fragment file with a path that is relative to the base directory
    return fs.readFileSync(`${baseDir}/${sanitizedFragmentFilename}`, 'utf8').trim();
  } catch (relativePathEx) {
    try {
      // It's possible the fragment file path was not relative so try again as an absolute path
      return fs.readFileSync(sanitizedFragmentFilename, 'utf8').trim();
    } catch (absolutePathEx) {
      console.error(`ERROR: Unable to read fragment file "${sanitizedFragmentFilename}": ${absolutePathEx}`);

      throw absolutePathEx;
    }
  }
}