import { readFile } from 'node:fs/promises';
import xxhash from 'xxhash-wasm';

/**
 * Initialize xxHash instance (singleton)
 */
let hasherInstance: Awaited<ReturnType<typeof xxhash>> | null = null;

async function getHasher() {
  if (!hasherInstance) {
    hasherInstance = await xxhash();
  }
  return hasherInstance;
}

/**
 * Compute xxHash64 checksum for a file
 *
 * @param filePath - Path to file
 * @returns Hex string of xxHash64 checksum
 */
export async function computeFileChecksum(filePath: string): Promise<string> {
  const hasher = await getHasher();
  const content = await readFile(filePath);
  // Use h64Raw for binary data (returns bigint), then convert to hex string
  const hash = hasher.h64Raw(content);
  return hash.toString(16);
}

/**
 * Compute xxHash64 checksum for a buffer
 *
 * @param data - Buffer to hash
 * @returns Hex string of xxHash64 checksum
 */
export async function computeBufferChecksum(data: Buffer): Promise<string> {
  const hasher = await getHasher();
  // Use h64Raw for binary data (returns bigint), then convert to hex string
  const hash = hasher.h64Raw(data);
  return hash.toString(16);
}