/** Download-URL (href der API) → dieselbe URL mit ?inline=1 für Anzeige */
export function hrefToInlineView(href) {
  if (!href) return href;
  const u = new URL(href, window.location.origin);
  u.searchParams.set('inline', '1');
  return u.pathname + u.search + u.hash;
}

const TEXT_PREVIEW_MAX = 512 * 1024;

/** @param {string} mime @param {string} fileName */
export function attachmentPreviewKind(mime, fileName) {
  const m = (mime || '').toLowerCase().trim();
  const ext = (fileName || '').split('.').pop()?.toLowerCase() || '';
  if (m.startsWith('image/')) return 'image';
  if (m === 'application/pdf' || ext === 'pdf') return 'pdf';
  if (m.startsWith('video/')) return 'video';
  if (m.startsWith('audio/')) return 'audio';
  if (
    m.startsWith('text/') ||
    m === 'application/json' ||
    m === 'application/xml' ||
    ['csv', 'json', 'xml', 'txt', 'log', 'md', 'svg'].includes(ext)
  ) {
    return 'text';
  }
  return 'other';
}

let dialogEl;
let bodyEl;
let titleEl;
let downloadLink;

function setPageScrollLocked(locked) {
  if (locked) {
    document.documentElement.style.overflow = 'hidden';
    document.body.style.overflow = 'hidden';
  } else {
    document.documentElement.style.overflow = '';
    document.body.style.overflow = '';
  }
}

function ensureDialog() {
  if (dialogEl) return;
  dialogEl = document.createElement('dialog');
  dialogEl.className = 'attachment-preview-dialog';
  dialogEl.setAttribute('aria-modal', 'true');
  dialogEl.innerHTML = `
    <div class="attachment-preview-inner">
      <header class="attachment-preview-header">
        <h3 class="attachment-preview-title"></h3>
        <button type="button" class="attachment-preview-close" aria-label="Schließen">×</button>
      </header>
      <div class="attachment-preview-body"></div>
      <footer class="attachment-preview-footer">
        <a class="button secondary attachment-preview-download" href="#" download>Herunterladen</a>
      </footer>
    </div>`;
  document.body.appendChild(dialogEl);
  bodyEl = dialogEl.querySelector('.attachment-preview-body');
  titleEl = dialogEl.querySelector('.attachment-preview-title');
  downloadLink = dialogEl.querySelector('.attachment-preview-download');
  dialogEl.querySelector('.attachment-preview-close').addEventListener('click', () => {
    dialogEl.close();
  });
  dialogEl.addEventListener('click', (e) => {
    if (e.target === dialogEl) dialogEl.close();
  });
  dialogEl.addEventListener('close', () => {
    if (bodyEl) bodyEl.innerHTML = '';
    setPageScrollLocked(false);
  });
}

/**
 * Klick-Delegation: Links mit .js-attachment-preview öffnen das Modal.
 */
export function bindAttachmentPreview(root = document.body) {
  ensureDialog();
  root.addEventListener('click', (e) => {
    const a = e.target.closest('a.js-attachment-preview');
    if (!a) return;
    e.preventDefault();
    openAttachmentPreview(a);
  });
}

/**
 * @param {HTMLAnchorElement} a
 */
export async function openAttachmentPreview(a) {
  ensureDialog();
  const name = a.getAttribute('data-name') || a.textContent?.trim() || 'Datei';
  const mime = a.getAttribute('data-mime') || '';
  const rawHref = a.getAttribute('href') || '';
  const viewUrl = hrefToInlineView(rawHref);
  const kind = attachmentPreviewKind(mime, name);

  titleEl.textContent = name;
  downloadLink.href = rawHref;
  downloadLink.setAttribute('download', name);

  bodyEl.className = 'attachment-preview-body attachment-preview-body--scroll';
  bodyEl.innerHTML = '<p class="muted attachment-preview-loading">Lade Vorschau …</p>';

  try {
    if (kind === 'image') {
      bodyEl.innerHTML = '';
      const img = document.createElement('img');
      img.className = 'attachment-preview-img';
      img.alt = name;
      img.src = viewUrl;
      img.referrerPolicy = 'same-origin';
      bodyEl.appendChild(img);
    } else if (kind === 'pdf') {
      bodyEl.className = 'attachment-preview-body attachment-preview-body--embed';
      bodyEl.innerHTML = '';
      const iframe = document.createElement('iframe');
      iframe.className = 'attachment-preview-iframe';
      iframe.title = name;
      iframe.src = viewUrl;
      bodyEl.appendChild(iframe);
    } else if (kind === 'video') {
      bodyEl.innerHTML = '';
      const v = document.createElement('video');
      v.className = 'attachment-preview-video';
      v.controls = true;
      v.playsInline = true;
      v.src = viewUrl;
      bodyEl.appendChild(v);
    } else if (kind === 'audio') {
      bodyEl.innerHTML = '';
      const v = document.createElement('audio');
      v.className = 'attachment-preview-audio';
      v.controls = true;
      v.src = viewUrl;
      bodyEl.appendChild(v);
    } else if (kind === 'text') {
      const res = await fetch(viewUrl, { credentials: 'include' });
      if (!res.ok) throw new Error('Laden fehlgeschlagen');
      let text = await res.text();
      if (text.length > TEXT_PREVIEW_MAX) {
        text = `${text.slice(0, TEXT_PREVIEW_MAX)}\n\n… (gekürzt)`;
      }
      bodyEl.innerHTML = '';
      const pre = document.createElement('pre');
      pre.className = 'attachment-preview-text';
      pre.textContent = text;
      bodyEl.appendChild(pre);
    } else {
      bodyEl.innerHTML =
        '<p class="muted">Für diesen Dateityp gibt es keine eingebaute Vorschau. Nutzen Sie „Herunterladen“.</p>';
    }
  } catch (err) {
    bodyEl.className = 'attachment-preview-body attachment-preview-body--scroll';
    bodyEl.innerHTML = `<p class="error">Vorschau konnte nicht geladen werden: ${err.message || err}</p>`;
  }

  if (typeof dialogEl.showModal === 'function') {
    setPageScrollLocked(true);
    dialogEl.showModal();
  }
}