import type { GitStore } from "../git/store";

const BINARY_SNIFF = 8000;

export type BoundedBlob = { size: number; bytes: Uint8Array | null; binary: boolean };

/**
 * Reads a blob only when it fits `maxBytes`: the size comes from the blob handle before any bytes are
 * copied, so a huge file costs a metadata read rather than a full buffer. Oversized blobs still get a
 * binary sniff from a bounded slice.
 */
export async function readBounded(store: GitStore, sha: string, maxBytes: number): Promise<BoundedBlob | null> {
  const handle = await store.blobStream(sha);
  if (!handle) return null;
  if (handle.size > maxBytes) {
    const head = new Uint8Array(await handle.slice(0, BINARY_SNIFF).arrayBuffer());
    return { size: handle.size, bytes: null, binary: head.includes(0) };
  }
  const bytes = new Uint8Array(await handle.arrayBuffer());
  return { size: handle.size, bytes, binary: bytes.subarray(0, BINARY_SNIFF).includes(0) };
}