/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.hash;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;

An OutputStream that maintains a hash of the data written to it. 
Author:
Nick Piepmeier
Since:
16.0/**
 * An {@link OutputStream} that maintains a hash of the data written to it.
 *
 * @author Nick Piepmeier
 * @since 16.0
 */
@Beta
public final class HashingOutputStream extends FilterOutputStream {
  private final Hasher hasher;

  
Creates an output stream that hashes using the given HashFunction, and forwards all data written to it to the underlying OutputStream. 
The OutputStream should not be written to before or after the hand-off. /**
   * Creates an output stream that hashes using the given {@link HashFunction}, and forwards all
   * data written to it to the underlying {@link OutputStream}.
   *
   * <p>The {@link OutputStream} should not be written to before or after the hand-off.
   */
  // TODO(user): Evaluate whether it makes sense to always piggyback the computation of a
  // HashCode on an existing OutputStream, compared to creating a separate OutputStream that could
  // be (optionally) be combined with another if needed (with something like
  // MultiplexingOutputStream).
  public HashingOutputStream(HashFunction hashFunction, OutputStream out) {
    super(checkNotNull(out));
    this.hasher = checkNotNull(hashFunction.newHasher());
  }

  @Override
  public void write(int b) throws IOException {
    hasher.putByte((byte) b);
    out.write(b);
  }

  @Override
  public void write(byte[] bytes, int off, int len) throws IOException {
    hasher.putBytes(bytes, off, len);
    out.write(bytes, off, len);
  }

  
Returns the HashCode based on the data written to this stream. The result is unspecified if this method is called more than once on the same instance. /**
   * Returns the {@link HashCode} based on the data written to this stream. The result is
   * unspecified if this method is called more than once on the same instance.
   */
  public HashCode hash() {
    return hasher.hash();
  }

  // Overriding close() because FilterOutputStream's close() method pre-JDK8 has bad behavior:
  // it silently ignores any exception thrown by flush(). Instead, just close the delegate stream.
  // It should flush itself if necessary.
  @Override
  public void close() throws IOException {
    out.close();
  }
}