/** Downloads through the authenticated canvas export route, including cross-origin media. */
export async function downloadCanvasMedia(files: Array<{ url: string; name: string }>) {
  if (!files.length) throw Error("没有可下载的素材");
  if (files.length > 200) throw Error("每次最多下载 200 项，请分批选择");
  const batch = files.length > 1;
  const response = await fetch(batch ? "/api/canvas/download-zip" : "/api/canvas/download-image", {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify(batch ? { files, folderName: "画布素材" } : files[0]),
    signal: AbortSignal.timeout(300000),
  });
  if (!response.ok) {
    const data = await response.json().catch(() => ({}));
    throw Error(data.error || "素材下载失败");
  }
  const blob = await response.blob();
  if (!blob.size) throw Error("返回的下载文件为空");
  const encodedName = response.headers
    .get("content-disposition")
    ?.match(/filename\*=UTF-8''([^;]+)/i)?.[1];
  const filename = encodedName
    ? decodeURIComponent(encodedName)
    : batch
      ? "画布素材.zip"
      : files[0].name;
  const url = URL.createObjectURL(blob);
  const link = document.createElement("a");
  link.href = url;
  link.download = filename;
  document.body.appendChild(link);
  link.click();
  link.remove();
  window.setTimeout(() => URL.revokeObjectURL(url), 60000);
  return { failed: Number(response.headers.get("X-Download-Failed-Count") || 0) };
}