/*
 * Copyright (C) 2013 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 java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

import com.google.common.annotations.Beta;

/**
 * An {@link InputStream} that maintains a hash of the data read from it.
 *
 * @author Qian Huang
 * @since 16.0
 */
@Beta
public final class HashingInputStream extends FilterInputStream {
	private final Hasher hasher;

	/**
	 * Creates an input stream that hashes using the given {@link HashFunction} and
	 * delegates all data read from it to the underlying {@link InputStream}.
	 *
	 * <p>
	 * The {@link InputStream} should not be read from before or after the hand-off.
	 */
	public HashingInputStream(HashFunction hashFunction, InputStream in) {
		super(checkNotNull(in));
		this.hasher = checkNotNull(hashFunction.newHasher());
	}

	/**
	 * Reads the next byte of data from the underlying input stream and updates the
	 * hasher with the byte read.
	 */
	@Override
	public int read() throws IOException {
		int b = in.read();
		if (b != -1) {
			hasher.putByte((byte) b);
		}
		return b;
	}

	/**
	 * Reads the specified bytes of data from the underlying input stream and
	 * updates the hasher with the bytes read.
	 */
	@Override
	public int read(byte[] bytes, int off, int len) throws IOException {
		int numOfBytesRead = in.read(bytes, off, len);
		if (numOfBytesRead != -1) {
			hasher.putBytes(bytes, off, numOfBytesRead);
		}
		return numOfBytesRead;
	}

	/**
	 * mark() is not supported for HashingInputStream
	 * 
	 * @return {@code false} always
	 */
	@Override
	public boolean markSupported() {
		return false;
	}

	/**
	 * mark() is not supported for HashingInputStream
	 */
	@Override
	public void mark(int readlimit) {
	}

	/**
	 * reset() is not supported for HashingInputStream.
	 * 
	 * @throws IOException this operation is not supported
	 */
	@Override
	public void reset() throws IOException {
		throw new IOException("reset not supported");
	}

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