export const MAX_FETCH_RESPONSE_BYTES = 10 * 1024 * 1024;

export async function readBoundedResponseBytes(response: Response, maxBytes: number) {
  const contentLength = Number(response.headers.get("content-length"));
  if (Number.isFinite(contentLength) && contentLength > maxBytes) {
    await response.body?.cancel();
    throw new Error(`URL response exceeds the ${Math.floor(maxBytes / (1024 * 1024))} MiB download limit.`);
  }

  const reader = response.body?.getReader();
  if (!reader) return new Uint8Array();
  const chunks: Uint8Array[] = [];
  let totalBytes = 0;
  try {
    while (true) {
      const { done, value } = await reader.read();
      if (done) break;
      totalBytes += value.byteLength;
      if (totalBytes > maxBytes) {
        await reader.cancel();
        throw new Error(`URL response exceeds the ${Math.floor(maxBytes / (1024 * 1024))} MiB download limit.`);
      }
      chunks.push(value);
    }
  } finally {
    reader.releaseLock();
  }

  const bytes = new Uint8Array(totalBytes);
  let offset = 0;
  for (const chunk of chunks) {
    bytes.set(chunk, offset);
    offset += chunk.byteLength;
  }
  return bytes;
}