/** 商品无图时的占位（小程序端无本地兜底图时用空串由 UI 显示灰底） */
export const PRODUCT_IMAGE_FALLBACK = '';

export type ProductImageSource = {
  mainImageUrl?: string | null;
  carouselUrls?: string[] | null;
  detailImageUrls?: string[] | null;
};

function uniqueUrls(urls: Array<string | null | undefined>) {
  const seen = new Set<string>();
  const result: string[] = [];
  for (const url of urls) {
    if (!url || seen.has(url)) continue;
    seen.add(url);
    result.push(url);
  }
  return result;
}

export function getProductMainImage(source?: ProductImageSource | null): string {
  return source?.mainImageUrl ?? source?.carouselUrls?.[0] ?? PRODUCT_IMAGE_FALLBACK;
}

export function getProductImages(source?: ProductImageSource | null): string[] {
  const carousel = uniqueUrls(source?.carouselUrls ?? []);
  if (carousel.length > 0) return carousel;
  const main = source?.mainImageUrl;
  if (main) return [main];
  return PRODUCT_IMAGE_FALLBACK ? [PRODUCT_IMAGE_FALLBACK] : [];
}

/** 详情页顶部轮播 */
export function getProductCarouselImages(source?: ProductImageSource | null): string[] {
  const carousel = uniqueUrls(source?.carouselUrls ?? []);
  if (carousel.length > 0) return carousel;
  return getProductImages(source);
}

/** 详情页图文长图 */
export function getProductDetailImages(source?: ProductImageSource | null): string[] {
  return uniqueUrls(source?.detailImageUrls ?? []);
}

export const FALLBACK_CITY_CODE = '410100';