remark-variables.js

/* eslint-env node */
/* eslint import/no-nodejs-modules:0 */
/* eslint-disable no-console */

import {visit} from 'unist-util-visit';

function scopedEval(expr, context = {}) {
  // eslint-disable-next-line no-new-func
  const evaluator = Function.apply(null, [
    ...Object.keys(context),
    'expr',
    'return eval(expr)',
  ]);
  return evaluator.apply(null, [...Object.values(context), expr]);
}

const matchEach = (text, pattern, callback) => {
  let match, rv;
  const promises = [];
  // eslint-disable-next-line no-cond-assign
  while ((match = pattern.exec(text)) !== null) {
    rv = callback(match);
    if (rv instanceof Promise) {
      promises.push(rv);
    }
  }
  return Promise.all(promises);
};

export default function remarkVariables(options) {
  return async (markdownAST, markdownNode) => {
    const page = markdownNode.data?.frontmatter;

    const scope = await options.resolveScopeData();

    visit(
      markdownAST,
      () => true,
      node => {
        // XXX(dcramer): by far the worst template language of all time

        if (!node.value) {
          return;
        }

        // TODO(dcramer): this could be improved by parsing the string piece by piece so you can
        // safely quote template literals e.g. {{ '{{ foo }}' }}
        matchEach(node.value, /\{\{\\?@inject (\s*[^}]+) \}\}/gi, match => {
          const expr = match[1].trim();

          // Inject sequence is escaped
          if (match[0].includes('{{\\@inject')) {
            node.value = node.value.replace('\\@inject', '@inject');
            return;
          }

          // YOU CAN EXECUTE CODE HERE JUST FYI
          let result;
          try {
            result = scopedEval(expr, {...scope, page});
          } catch (err) {
            console.error(`Failed to interpolate expression: "${expr}"`);
            throw err;
          }

          // replace the match with the result (even if it's empty)
          node.value = node.value.replace(match[0], result);
          if (!result) {
            console.error(new Error(`Failed to interpolate expression: "${expr}"`));
            // fail the build process in production
            if (process.env.NODE_ENV === 'production') {
              process.exit(1);
            }
          }
        });
      }
    );
  };
}