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

/**
 * @typedef {import('@types/mdast').Root} Root - https://github.com/syntax-tree/mdast#root
 * @typedef {import('@types/mdast').Heading} Heading - https://github.com/syntax-tree/mdast#heading
 */

/**
 * Find all headings within a MDX document, and export them as JS array.
 * This uses the MDAST's `heading` and tries to guess the children's content.
 * When the node has an ID, generated by `remark-slug`, the ID is added to the exported object.
 *
 * @param {object} options
 * @param {string} [options.exportName="headings"]
 */
export default function remarkExportHeadings(options = {}) {
  const { exportName = 'headings' } = options;

  /** @param {Root} tree */
  return tree => {
    const headings = [];

    /** @param {Heading} node */
    const visitor = node => {
      if (node.children.length > 0) {
        headings.push({
          id: node.data?.id,
          depth: node.depth,
          type: node.children.find(node => node.type !== 'text')?.type || 'text',
          title: node.children.map(child => child.value).join(' '),
        });
      }
    };

    visit(tree, 'heading', visitor);

    tree.children.push({
      type: 'mdxjsEsm',
      data: {
        estree: parse(`export const ${exportName} = ${JSON.stringify(headings)};`, {
          sourceType: 'module',
          ecmaVersion: 2022,
        }),
      },
    });
  };
}