/*
 * 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.
 */
/**
 * Copyright (c) 2005, European Commission project OneLab under contract 034819
 * (http://www.one-lab.org)
 * <p>
 * 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.
 * <p>
 * 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.
 */

package org.apache.hudi.common.bloom;

import org.apache.hudi.common.util.hash.Hash;

/**
 * Implements a hash object that returns a certain number of hashed values.
 * <p>
 * The code in class is ported from {@link org.apache.hadoop.util.bloom.HashFunction} in Apache Hadoop.
 *
 * @see Key The general behavior of a key being stored in a bloom filter
 * @see InternalBloomFilter The general behavior of a bloom filter
 */
public final class HashFunction {
  /**
   * The number of hashed values.
   */
  private int nbHash;

  /**
   * The maximum highest returned value.
   */
  private int maxValue;

  /**
   * Hashing algorithm to use.
   */
  private Hash hashFunction;

  /**
   * Constructor.
   * <p>
   * Builds a hash function that must obey to a given maximum number of returned values and a highest value.
   *
   * @param maxValue The maximum highest returned value.
   * @param nbHash   The number of resulting hashed values.
   * @param hashType type of the hashing function (see {@link Hash}).
   */
  public HashFunction(int maxValue, int nbHash, int hashType) {
    if (maxValue <= 0) {
      throw new IllegalArgumentException("maxValue must be > 0");
    }

    if (nbHash <= 0) {
      throw new IllegalArgumentException("nbHash must be > 0");
    }

    this.maxValue = maxValue;
    this.nbHash = nbHash;
    this.hashFunction = Hash.getInstance(hashType);
    if (this.hashFunction == null) {
      throw new IllegalArgumentException("hashType must be known");
    }
  }

  /**
   * Clears <i>this</i> hash function. A NOOP
   */
  public void clear() {
  }

  /**
   * Hashes a specified key into several integers.
   *
   * @param k The specified key.
   * @return The array of hashed values.
   */
  public int[] hash(Key k) {
    byte[] b = k.getBytes();
    if (b == null) {
      throw new NullPointerException("buffer reference is null");
    }
    if (b.length == 0) {
      throw new IllegalArgumentException("key length must be > 0");
    }
    int[] result = new int[nbHash];
    for (int i = 0, initval = 0; i < nbHash; i++) {
      initval = hashFunction.hash(b, initval);
      result[i] = Math.abs(initval % maxValue);
    }
    return result;
  }
}
