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/*
 * Original Guava code is copyright (C) 2015 The Guava Authors.
 * Modifications from Guava are copyright (C) 2016 DiffPlug.
 *
 * 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.diffplug.common.hash;

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

import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

import javax.annotation.CheckReturnValue;

import com.diffplug.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}.
	 *
	 * 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
	@CheckReturnValue
	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.
	 */
	@CheckReturnValue
	public HashCode hash() {
		return hasher.hash();
	}
}