/*
    * 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 {@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 {@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 {@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();
    }
  }