import DOMPurify from 'dompurify';
import { lexer, marked } from 'marked';
import type { Token } from 'marked';

const stripHtmlTags = (html: string): string => html.replace(/<[^>]*>/g, ' ');

const getInlineText = (tokens: Token[]): string => tokens.map(getTokenText).join('');

function getTokenText(token: Token): string {
  switch (token.type) {
    case 'space':
    case 'hr':
    case 'br':
    case 'def':
      return '';
    case 'code':
    case 'codespan':
    case 'escape':
      return token.text;
    case 'html':
      return stripHtmlTags(token.text);
    case 'image':
      return token.text;
    case 'blockquote':
    case 'list_item':
      return (token.tokens ?? []).map(getTokenText).join(' ');
    case 'list':
      return token.items.map(getTokenText).join(' ');
    case 'table': {
      const cells = [
        ...token.header,
        ...token.rows.flat(),
      ];
      return cells.map(cell => getInlineText(cell.tokens)).join(' ');
    }
    default:
      if ('tokens' in token && token.tokens) {
        return getInlineText(token.tokens);
      }
      return 'text' in token && typeof token.text === 'string'
        ? token.text
        : '';
  }
}

/**
 * Converts Markdown into compact plain text for single-line message previews.
 */
export function markdownToPlainText(markdown: string): string {
  if (!markdown) {
    return '';
  }

  return lexer(markdown, { gfm: true })
    .map(getTokenText)
    .join(' ')
    .replace(/\s+/g, ' ')
    .trim();
}

export function renderMarkdown(markdown: string): string {
  if (!markdown) {
    return '';
  }

  // `marked` does not sanitize its output, so the HTML it produces from a
  // remote message is untrusted. Every HTML string this package hands to
  // `dangerouslySetInnerHTML` must go through DOMPurify first.
  const html = marked.parse(markdown, { async: false });

  // DOMPurify needs a DOM. Without one it returns the input unchanged, which
  // would emit unsanitized HTML, so fail closed instead.
  if (!DOMPurify.isSupported) {
    return '';
  }

  return DOMPurify.sanitize(html);
}