import { visit } from 'unist-util-visit';
import { toString } from 'mdast-util-to-string';

import fs from 'node:fs';

// build table of contents and inject into frontmatter
export function localRemark() {
    return (tree, vfile) => {
        if (vfile.data.fm.toc === false) {
            return;
        }

        let toc = [];
        let description = null;
        
        visit(tree, ['heading', 'paragraph'], node => {
            // build table of contents and inject into frontmatter
            if (node.type === 'heading') {
                toc.push({
                    text: toString(node),
                    depth: node.depth,
                });
            }

            // inject description (first 25 words of the first paragraph)
            if (node.type === 'paragraph' && description === null) {
                description = summarize(node);
            }
        });

        vfile.data.fm.toc = toc;
        vfile.data.fm.description = description;
    }
}


// convert paragraph to single string after stripping everything between html tags
function summarize(par) {
    let newChildren = [];
    let push = true;
    for (const child of par.children) {
        if (child.type === 'html') {
            push = !push;
            continue;
        }
        if (push) {
            newChildren.push(child);
        }
    }

    return toString({type: 'paragraph', children: newChildren});
}