/*
 * 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.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import java.io.Serializable;
import java.util.zip.Checksum;

import com.google.common.base.Supplier;

/**
 * {@link HashFunction} adapter for {@link Checksum} instances.
 *
 * @author Colin Decker
 */
final class ChecksumHashFunction extends AbstractStreamingHashFunction implements Serializable {

	private final Supplier<? extends Checksum> checksumSupplier;
	private final int bits;
	private final String toString;

	ChecksumHashFunction(Supplier<? extends Checksum> checksumSupplier, int bits, String toString) {
		this.checksumSupplier = checkNotNull(checksumSupplier);
		checkArgument(bits == 32 || bits == 64, "bits (%s) must be either 32 or 64", bits);
		this.bits = bits;
		this.toString = checkNotNull(toString);
	}

	@Override
	public int bits() {
		return bits;
	}

	@Override
	public Hasher newHasher() {
		return new ChecksumHasher(checksumSupplier.get());
	}

	@Override
	public String toString() {
		return toString;
	}

	/**
	 * Hasher that updates a checksum.
	 */
	private final class ChecksumHasher extends AbstractByteHasher {

		private final Checksum checksum;

		private ChecksumHasher(Checksum checksum) {
			this.checksum = checkNotNull(checksum);
		}

		@Override
		protected void update(byte b) {
			checksum.update(b);
		}

		@Override
		protected void update(byte[] bytes, int off, int len) {
			checksum.update(bytes, off, len);
		}

		@Override
		public HashCode hash() {
			long value = checksum.getValue();
			if (bits == 32) {
				/*
				 * The long returned from a 32-bit Checksum will have all 0s for its second
				 * word, so the cast won't lose any information and is necessary to return a
				 * HashCode of the correct size.
				 */
				return HashCode.fromInt((int) value);
			} else {
				return HashCode.fromLong(value);
			}
		}
	}

	private static final long serialVersionUID = 0L;
}
