import type { Root, Paragraph, PhrasingContent } from 'mdast';
import type { VFile } from 'vfile';
import { visit } from 'unist-util-visit';
import { toString } from 'mdast-util-to-string';


export function remarkDescription() {
    return (tree: Root, vfile: VFile) => {
        let description: string | null = null;

        visit(tree, 'paragraph', (node: Paragraph) => {
            if (description !== null) return;
            description = summarize(node);
        });

        // Astro exposes this as `remarkPluginFrontmatter` from render()
        const astro = (vfile.data.astro ??= { frontmatter: {} }) as { frontmatter: Record<string, unknown> };
        astro.frontmatter.description = description;
    };
}


/**
 * Convert a paragraph node to a plain-text string, stripping any
 * MDX JSX elements (e.g. <Sidenote>) so their content doesn't
 * leak into the summary.
 */
function summarize(par: Paragraph): string {
    const filtered = par.children.filter(
        (child: PhrasingContent) => !(child.type as string).startsWith('mdxJsx')
    );
    return toString({ type: 'paragraph', children: filtered });
}