/*
 * 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.hudi.common.util.hash;

import org.apache.hudi.common.bloom.InternalBloomFilter;

/**
 * This class represents a common API for hashing functions used by
 * {@link InternalBloomFilter}.
 * <p>
 * The code in class is ported from {@link org.apache.hadoop.util.hash.Hash} in Apache Hadoop.
 */
public abstract class Hash {
  /**
   * Constant to denote invalid hash type.
   */
  public static final int INVALID_HASH = -1;
  /**
   * Constant to denote {@link JenkinsHash}.
   */
  public static final int JENKINS_HASH = 0;
  /**
   * Constant to denote {@link MurmurHash}.
   */
  public static final int MURMUR_HASH = 1;

  /**
   * This utility method converts String representation of hash function name
   * to a symbolic constant. Currently two function types are supported,
   * "jenkins" and "murmur".
   *
   * @param name hash function name
   * @return one of the predefined constants
   */
  public static int parseHashType(String name) {
    if ("jenkins".equalsIgnoreCase(name)) {
      return JENKINS_HASH;
    } else if ("murmur".equalsIgnoreCase(name)) {
      return MURMUR_HASH;
    } else {
      return INVALID_HASH;
    }
  }

  /**
   * Get a singleton instance of hash function of a given type.
   *
   * @param type predefined hash type
   * @return hash function instance, or null if type is invalid
   */
  public static Hash getInstance(int type) {
    switch (type) {
      case JENKINS_HASH:
        return JenkinsHash.getInstance();
      case MURMUR_HASH:
        return MurmurHash.getInstance();
      default:
        return null;
    }
  }

  /**
   * Calculate a hash using all bytes from the input argument, and
   * a seed of -1.
   *
   * @param bytes input bytes
   * @return hash value
   */
  public int hash(byte[] bytes) {
    return hash(bytes, bytes.length, -1);
  }

  /**
   * Calculate a hash using all bytes from the input argument,
   * and a provided seed value.
   *
   * @param bytes   input bytes
   * @param initval seed value
   * @return hash value
   */
  public int hash(byte[] bytes, int initval) {
    return hash(bytes, bytes.length, initval);
  }

  /**
   * Calculate a hash using bytes from 0 to <code>length</code>, and
   * the provided seed value
   *
   * @param bytes   input bytes
   * @param length  length of the valid bytes to consider
   * @param initval seed value
   * @return hash value
   */
  public abstract int hash(byte[] bytes, int length, int initval);
}
