const FALLBACK_MANIFEST = {
  variants: {
    mobile: { folder: 'mobile-image', images: [] },
    desktop: { folder: 'desketop-image', images: [] },
  },
};

export async function loadManifest(request) {
  try {
    const response = await fetch(new URL('/manifest.json', request.url));
    if (!response.ok) return FALLBACK_MANIFEST;
    return await response.json();
  } catch {
    return FALLBACK_MANIFEST;
  }
}

export function detectVariant(request) {
  const url = new URL(request.url);
  const params = url.searchParams;
  const mode = (params.get('mode') || 'auto').toLowerCase();
  const orientation = (params.get('orientation') || '').toLowerCase();
  const device = (params.get('device') || '').toLowerCase();
  const ua = (request.headers.get('user-agent') || '').toLowerCase();
  const chMobile = request.headers.get('sec-ch-ua-mobile');

  if (mode === 'mobile' || mode === 'desktop') return mode;
  if (orientation === 'portrait' || orientation === 'vertical') return 'mobile';
  if (orientation === 'landscape' || orientation === 'horizontal') return 'desktop';
  if (device === 'mobile' || device === 'desktop') return device;
  if (chMobile === '?1') return 'mobile';
  if (chMobile === '?0') return 'desktop';
  if (['mobi', 'android', 'iphone', 'ipad', 'ipod', 'phone'].some((token) => ua.includes(token))) return 'mobile';
  return 'desktop';
}

export function getVariantPayload(manifest, variant) {
  const data = manifest?.variants?.[variant] || {};
  const folder = data.folder || (variant === 'mobile' ? 'mobile-image' : 'desketop-image');
  const images = Array.isArray(data.images)
    ? data.images.filter((name) => typeof name === 'string' && name.toLowerCase().endsWith('.webp'))
    : [];
  return { folder, images };
}

export function buildAssetUrl(request, folder, filename) {
  return new URL(`/${folder}/${filename}`, request.url).toString();
}

export function pickRandom(items) {
  return items[Math.floor(Math.random() * items.length)];
}