docs/packages/epub/src/markdown-to-html.ts

import type { Transformer } from 'unified';
import remarkGfm from 'remark-gfm';
import remarkRehype from 'remark-rehype';
import rehypeStringify from 'rehype-stringify';
import type { Root } from 'mdast';
import { visit } from 'unist-util-visit';
import { remark } from 'remark';
import { resolveImageSrc } from './image-resolver';

const processor = remark()
  .use(remarkGfm)
  .use(remarkResolveImg)
  .use(remarkRehype, { allowDangerousHtml: true })
  .use(rehypeStringify, { allowDangerousHtml: true });

declare module 'vfile' {
  export interface DataMap {
    pageDir: string;
    publicDir: string;
  }
}

function remarkResolveImg(): Transformer<Root, Root> {
  return (tree, file) => {
    const { pageDir, publicDir } = file.data;
    if (!pageDir || !publicDir) return;

    visit(tree, 'image', (node, idx, parent) => {
      const resolved = resolveImageSrc(node.url, pageDir, publicDir);
      if (resolved) {
        node.url = resolved;
      } else if (idx !== undefined && parent) {
        parent.children.splice(idx, 1);
      }
    });
  };
}

/**
 * Convert markdown string to HTML suitable for EPUB chapters.
 * Uses unified pipeline: remark-parse -> remark-gfm -> remark-rehype -> rehype-stringify
 */
export async function markdownToHtml(
  markdown: string,
  pageDir: string,
  publicDir: string,
): Promise<string> {
  const result = await processor.process({
    value: markdown,
    data: {
      pageDir,
      publicDir,
    },
  });
  return String(result);
}