/*
    * 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 com.google.common.base.Supplier;
  
  import java.io.Serializable;
  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<? 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;
  }