/**
 *
 * Copyright (c) 2005, European Commission project OneLab under contract 034819 (http://www.one-lab.org)
 * All rights reserved.
 * Redistribution and use in source and binary forms, with or 
 * without modification, are permitted provided that the following 
 * conditions are met:
 *  - Redistributions of source code must retain the above copyright 
 *    notice, this list of conditions and the following disclaimer.
 *  - Redistributions in binary form must reproduce the above copyright 
 *    notice, this list of conditions and the following disclaimer in 
 *    the documentation and/or other materials provided with the distribution.
 *  - Neither the name of the University Catholique de Louvain - UCL
 *    nor the names of its contributors may be used to endorse or 
 *    promote products derived from this software without specific prior 
 *    written permission.
 *    
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 
 * POSSIBILITY OF SUCH DAMAGE.
 */

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.hadoop.util.bloom;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.io.WritableComparable;

/**
 * The general behavior of a key that must be stored in a filter.
 * 
 * @see Filter The general behavior of a filter
 */
@InterfaceAudience.LimitedPrivate({"HDFS", "MapReduce"})
@InterfaceStability.Unstable
public class Key implements WritableComparable<Key> {
  /** Byte value of key */
  byte[] bytes;
  
  /**
   * The weight associated to <i>this</i> key.
   * <p>
   * <b>Invariant</b>: if it is not specified, each instance of 
   * <code>Key</code> will have a default weight of 1.0
   */
  double weight;

  /** default constructor - use with readFields */
  public Key() {}

  /**
   * Constructor.
   * <p>
   * Builds a key with a default weight.
   * @param value The byte value of <i>this</i> key.
   */
  public Key(byte[] value) {
    this(value, 1.0);
  }

  /**
   * Constructor.
   * <p>
   * Builds a key with a specified weight.
   * @param value The value of <i>this</i> key.
   * @param weight The weight associated to <i>this</i> key.
   */
  public Key(byte[] value, double weight) {
    set(value, weight);
  }

  /**
   * @param value
   * @param weight
   */
  public void set(byte[] value, double weight) {
    if (value == null) {
      throw new IllegalArgumentException("value can not be null");
    }
    this.bytes = value;
    this.weight = weight;
  }
  
  /** @return byte[] The value of <i>this</i> key. */
  public byte[] getBytes() {
    return this.bytes;
  }

  /** @return Returns the weight associated to <i>this</i> key. */
  public double getWeight() {
    return weight;
  }

  /**
   * Increments the weight of <i>this</i> key with a specified value. 
   * @param weight The increment.
   */
  public void incrementWeight(double weight) {
    this.weight += weight;
  }

  /** Increments the weight of <i>this</i> key by one. */
  public void incrementWeight() {
    this.weight++;
  }

  @Override
  public boolean equals(Object o) {
    if (!(o instanceof Key)) {
      return false;
    }
    return this.compareTo((Key)o) == 0;
  }
  
  @Override
  public int hashCode() {
    int result = 0;
    for (int i = 0; i < bytes.length; i++) {
      result ^= Byte.valueOf(bytes[i]).hashCode();
    }
    result ^= Double.valueOf(weight).hashCode();
    return result;
  }

  // Writable

  @Override
  public void write(DataOutput out) throws IOException {
    out.writeInt(bytes.length);
    out.write(bytes);
    out.writeDouble(weight);
  }
  
  @Override
  public void readFields(DataInput in) throws IOException {
    this.bytes = new byte[in.readInt()];
    in.readFully(this.bytes);
    weight = in.readDouble();
  }
  
  // Comparable
  @Override
  public int compareTo(Key other) {
    int result = this.bytes.length - other.getBytes().length;
    for (int i = 0; result == 0 && i < bytes.length; i++) {
      result = this.bytes[i] - other.bytes[i];
    }
    
    if (result == 0) {
      result = (int)(this.weight - other.weight);
    }
    return result;
  }
}