*/
@Immutable
@ElementTypesAreNonnullByDefault
final class MessageDigestHashFunction extends AbstractHashFunction implements Serializable {

  @SuppressWarnings("Immutable") // cloned before each use
  private final MessageDigest prototype;

  private final int bytes;
  private final boolean supportsClone;
  private final String toString;

  MessageDigestHashFunction(String algorithmName, String toString) {

        assertEquals(
            HashCode.fromBytes(Arrays.copyOf(digest.digest(input), bytes)),
            new MessageDigestHashFunction(algorithmName, bytes, algorithmName).hashBytes(input));
      }
      try {
        int maxSize = digest.getDigestLength();
        new MessageDigestHashFunction(algorithmName, maxSize + 1, algorithmName);
        fail();
      } catch (IllegalArgumentException expected) {
      }

        assertEquals(
            HashCode.fromBytes(Arrays.copyOf(digest.digest(input), bytes)),
            new MessageDigestHashFunction(algorithmName, bytes, algorithmName).hashBytes(input));
      }
      try {
        int maxSize = digest.getDigestLength();
        new MessageDigestHashFunction(algorithmName, maxSize + 1, algorithmName);
        fail();
      } catch (IllegalArgumentException expected) {
      }

    static final HashFunction SHA_1 = new MessageDigestHashFunction("SHA-1", "Hashing.sha1()");
  }

  /** Returns a hash function implementing the SHA-256 algorithm (256 hash bits). */
  public static HashFunction sha256() {
    return Sha256Holder.SHA_256;
  }

  private static class Sha256Holder {
    static final HashFunction SHA_256 =
        new MessageDigestHashFunction("SHA-256", "Hashing.sha256()");
  }