/*
 * Copyright (C) 2012 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 static com.google.common.base.Preconditions.checkPositionIndexes;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;

import com.google.common.primitives.Chars;
import com.google.common.primitives.Ints;
import com.google.common.primitives.Longs;
import com.google.common.primitives.Shorts;

/**
 * Abstract {@link Hasher} that handles converting primitives to bytes using a
 * scratch {@code
 * ByteBuffer} and streams all bytes to a sink to compute the hash.
 *
 * @author Colin Decker
 */
abstract class AbstractByteHasher extends AbstractHasher {

	private final ByteBuffer scratch = ByteBuffer.allocate(8).order(ByteOrder.LITTLE_ENDIAN);

	/**
	 * Updates this hasher with the given byte.
	 */
	protected abstract void update(byte b);

	/**
	 * Updates this hasher with the given bytes.
	 */
	protected void update(byte[] b) {
		update(b, 0, b.length);
	}

	/**
	 * Updates this hasher with {@code len} bytes starting at {@code off} in the
	 * given buffer.
	 */
	protected void update(byte[] b, int off, int len) {
		for (int i = off; i < off + len; i++) {
			update(b[i]);
		}
	}

	@Override
	public Hasher putByte(byte b) {
		update(b);
		return this;
	}

	@Override
	public Hasher putBytes(byte[] bytes) {
		checkNotNull(bytes);
		update(bytes);
		return this;
	}

	@Override
	public Hasher putBytes(byte[] bytes, int off, int len) {
		checkPositionIndexes(off, off + len, bytes.length);
		update(bytes, off, len);
		return this;
	}

	/**
	 * Updates the sink with the given number of bytes from the buffer.
	 */
	private Hasher update(int bytes) {
		try {
			update(scratch.array(), 0, bytes);
		} finally {
			scratch.clear();
		}
		return this;
	}

	@Override
	public Hasher putShort(short s) {
		scratch.putShort(s);
		return update(Shorts.BYTES);
	}

	@Override
	public Hasher putInt(int i) {
		scratch.putInt(i);
		return update(Ints.BYTES);
	}

	@Override
	public Hasher putLong(long l) {
		scratch.putLong(l);
		return update(Longs.BYTES);
	}

	@Override
	public Hasher putChar(char c) {
		scratch.putChar(c);
		return update(Chars.BYTES);
	}

	@Override
	public <T> Hasher putObject(T instance, Funnel<? super T> funnel) {
		funnel.funnel(instance, this);
		return this;
	}
}
