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

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

/**
 * {@link HashFunction} adapter for {@link Checksum} instances.
 *
 * @author Colin Decker
 */
final class ChecksumHashFunction extends AbstractStreamingHashFunction implements Serializable {
	private final Supplier checksumSupplier;
	private final int bits;
	private final String toString;

	ChecksumHashFunction(Supplier 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;
}