(() => {
  const MarkdownIt = window.markdownit;
  const purifier = window.DOMPurify;
  const MAX_MARKDOWN_LENGTH = 256 * 1024;

  function safeExternalUrl(value) {
    const raw = String(value || '').trim();
    if (!/^https?:\/\//i.test(raw)) return '';
    try {
      const url = new URL(raw);
      if (!/^https?:$/.test(url.protocol) || url.username || url.password) return '';
      return url.toString();
    } catch (error) {
      return '';
    }
  }

  if (typeof MarkdownIt !== 'function' || !purifier || typeof purifier.sanitize !== 'function') {
    window.AiMarkdown = Object.freeze({
      available: false,
      mount(root, source) {
        root.classList.add('ai-output-plain');
        root.textContent = String(source || '');
      },
      externalUrl() {
        return '';
      }
    });
    return;
  }

  const markdown = new MarkdownIt({
    html: false,
    breaks: true,
    linkify: true,
    typographer: false
  });

  markdown.renderer.rules.link_open = (tokens, index, options, env, renderer) => {
    const token = tokens[index];
    const url = safeExternalUrl(token.attrGet('href'));
    token.attrSet('href', '#');
    if (url) {
      token.attrSet('data-external-url', url);
      token.attrSet('rel', 'noopener noreferrer');
    } else {
      token.attrJoin('class', 'ai-md-link-blocked');
      token.attrSet('aria-disabled', 'true');
    }
    return renderer.renderToken(tokens, index, options);
  };

  markdown.renderer.rules.image = (tokens, index) => {
    const alt = markdown.utils.escapeHtml(String(tokens[index].content || '').trim());
    const label = alt ? `图片：${alt}` : '外部图片已阻止';
    return `<span class="ai-md-image-placeholder" role="note">[${label}]</span>`;
  };

  const sanitizeOptions = Object.freeze({
    ALLOWED_TAGS: [
      'p', 'br', 'strong', 'em', 's', 'blockquote', 'pre', 'code',
      'ul', 'ol', 'li', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6',
      'table', 'thead', 'tbody', 'tr', 'th', 'td', 'hr', 'a', 'span'
    ],
    ALLOWED_ATTR: [
      'href', 'title', 'class', 'rel', 'role', 'aria-disabled', 'data-external-url'
    ],
    ALLOW_DATA_ATTR: true,
    ALLOW_ARIA_ATTR: true
  });

  function render(source) {
    return purifier.sanitize(markdown.render(String(source || '')), sanitizeOptions);
  }

  window.AiMarkdown = Object.freeze({
    available: true,
    render,
    mount(root, source) {
      const text = String(source || '');
      if (text.length > MAX_MARKDOWN_LENGTH) {
        root.classList.add('ai-output-plain');
        root.textContent = text;
        return;
      }
      root.classList.remove('ai-output-plain');
      root.innerHTML = render(text);
    },
    externalUrl(target) {
      const link = target && typeof target.closest === 'function'
        ? target.closest('a[data-external-url]')
        : null;
      return link ? safeExternalUrl(link.getAttribute('data-external-url')) : '';
    }
  });
})();