How to use the postcss-scss.parse function in postcss-scss

module.exports = (cssString, filePath, pathToVariables = '../variables') => {
  const root = postcssScss.parse(cssString, { from: filePath });

  const output = processRoot(root, filePath);

  // e.g styles.scss
  const isJustSassImports = root.nodes.every(
    node => node.type === 'atrule' && node.name === 'import',
  );
  if (isJustSassImports) return null;

  let fileIsJustVarExports = true;

  const classesEntries = Array.from(output.classes.entries());

  const oneDefault = classesEntries.filter(([, { isUsedInFile }]) => !isUsedInFile).length === 1;

  const emotionExports = classesEntries

const code = fs.readFileSync(file, 'utf8');
            let destinationFile = destinationDirectory + path.sep + file.replace(sourceDirectory, '');
            let tss = '';

            console.log('Transforming', file, 'to', destinationFile);

            switch (fileNameExtension(file)) {

                case "sass":
                    console.error('TODO: Sass not implemented yet, file will be empty!');
                    postcssSass.process(code).result.root;
                    sassFiles++;
                    break;
                case "scss":
                    console.error('TODO: Sass not implemented yet, file will be empty!');
                    postcssScss.parse(code);
                    scssFiles++;
                    break;
                case "less":
                    console.error('TODO: Sass not implemented yet, file will be empty!');
                    postcssLess.parse(code);
                    lessFiles++;
                    break;
                case "css":
                    tss = transformCSStoTSS(postcssCss.parse(code));
                    destinationFile = destinationFile.replace('.css', '.tss.ts');
                    cssFiles++;
            }

            if (!existsSync(destinationDirectory)) {
                mkdirSync(destinationDirectory);
            }

function parse(scssString, ignoreList) {
    const parsedScss = scssParse(scssString);
    const variables = [];

    parseNodes(parsedScss.nodes, variables, ignoreList);
    return variables;
}

parse(code) {
    this._ast = postcss.parse(code);
  }