interface BlobRef {
  $type: "blob";
  ref: {
    $link: string;
  };
  mimeType?: string;
  size?: number;
}

/**
 * Check if value is a blob reference
 */
export function isBlobRef(value: unknown): value is BlobRef {
  return (
    typeof value === "object" &&
    value !== null &&
    "$type" in value &&
    value.$type === "blob" &&
    "ref" in value &&
    typeof value.ref === "object" &&
    value.ref !== null &&
    "$link" in value.ref &&
    typeof value.ref.$link === "string"
  );
}

/**
 * Convert blob ref to CDN URL
 */
export function blobRefToCdnUrl(
  did: string,
  blobRef: BlobRef,
  preset: "avatar" | "banner" | "feed_thumbnail" | "feed_fullsize" = "feed_fullsize",
  cdnBaseUrl = "https://cdn.bsky.app/img"
): string {
  const cid = blobRef.ref.$link;
  return `${cdnBaseUrl}/${preset}/plain/${did}/${cid}@jpeg`;
}