/*
    * Copyright (C) 2011 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 com.google.common.base.Preconditions;
  
  import java.io.ByteArrayOutputStream;
  import java.io.IOException;
  import java.nio.charset.Charset;
  
  /**
   * Skeleton implementation of {@link HashFunction}, appropriate for non-streaming algorithms.
   * All the hash computation done using {@linkplain #newHasher()} are delegated to the {@linkplain
   * #hashBytes(byte[], int, int)} method.
   *
   * @author Dimitris Andreou
   */
  abstract class AbstractNonStreamingHashFunction implements HashFunction {
    @Override
    public Hasher newHasher() {
      return new BufferingHasher(32);
    }
  
    @Override
    public Hasher newHasher(int expectedInputSize) {
      Preconditions.checkArgument(expectedInputSize >= 0);
      return new BufferingHasher(expectedInputSize);
    }
  
    @Override public <T> HashCode hashObject(T instance, Funnel<? super T> funnel) {
      return newHasher().putObject(instance, funnel).hash();
    }
  
    @Override public HashCode hashUnencodedChars(CharSequence input) {
      int len = input.length();
      Hasher hasher = newHasher(len * 2);
      for (int i = 0; i < len; i++) {
        hasher.putChar(input.charAt(i));
      }
      return hasher.hash();
    }
  
    @Override public HashCode hashString(CharSequence input, Charset charset) {
      return hashBytes(input.toString().getBytes(charset));
    }
  
    @Override public HashCode hashInt(int input) {
      return newHasher(4).putInt(input).hash();
    }
  
    @Override public HashCode hashLong(long input) {
      return newHasher(8).putLong(input).hash();
    }
  
    @Override public HashCode hashBytes(byte[] input) {
      return hashBytes(input, 0, input.length);
    }
  
    /**
     * In-memory stream-based implementation of Hasher.
     */
    private final class BufferingHasher extends AbstractHasher {
      final ExposedByteArrayOutputStream stream;
      static final int BOTTOM_BYTE = 0xFF;
  
      BufferingHasher(int expectedInputSize) {
        this.stream = new ExposedByteArrayOutputStream(expectedInputSize);
      }
  
      @Override
      public Hasher putByte(byte b) {
        stream.write(b);
        return this;
      }
  
      @Override
      public Hasher putBytes(byte[] bytes) {
        try {
          stream.write(bytes);
        } catch (IOException e) {
          throw new RuntimeException(e);
        }
        return this;
      }
  
     @Override
     public Hasher putBytes(byte[] bytes, int off, int len) {
       stream.write(bytes, off, len);
       return this;
     }
 
     @Override
     public Hasher putShort(short s) {
       stream.write(s & BOTTOM_BYTE);
       stream.write((s >>> 8)  & BOTTOM_BYTE);
       return this;
     }
 
     @Override
     public Hasher putInt(int i) {
       stream.write(i & BOTTOM_BYTE);
       stream.write((i >>> 8) & BOTTOM_BYTE);
       stream.write((i >>> 16) & BOTTOM_BYTE);
       stream.write((i >>> 24) & BOTTOM_BYTE);
       return this;
     }
 
     @Override
     public Hasher putLong(long l) {
       for (int i = 0; i < 64; i += 8) {
         stream.write((byte) ((l >>> i) & BOTTOM_BYTE));
       }
       return this;
     }
 
     @Override
     public Hasher putChar(char c) {
       stream.write(c & BOTTOM_BYTE);
       stream.write((c >>> 8) & BOTTOM_BYTE);
       return this;
     }
 
     @Override
     public <T> Hasher putObject(T instance, Funnel<? super T> funnel) {
       funnel.funnel(instance, this);
       return this;
     }
 
     @Override
     public HashCode hash() {
       return hashBytes(stream.byteArray(), 0, stream.length());
     }
   }
 
   // Just to access the byte[] without introducing an unnecessary copy
   private static final class ExposedByteArrayOutputStream extends ByteArrayOutputStream {
     ExposedByteArrayOutputStream(int expectedInputSize) {
       super(expectedInputSize);
     }
     byte[] byteArray() {
       return buf;
     }
     int length() {
       return count;
     }
   }
 }