/*
 * 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.hbase.util.test;

import java.util.Random;

import org.apache.hadoop.hbase.util.Bytes;
import org.apache.hadoop.hbase.util.MD5Hash;

/**
 * A generator of random keys and values for load testing. Keys are generated
 * by converting numeric indexes to strings and prefixing them with an MD5
 * hash. Values are generated by selecting value size in the configured range
 * and generating a pseudo-random sequence of bytes seeded by key, column
 * qualifier, and value size.
 * <p>
 * Not thread-safe, so a separate instance is needed for every writer thread/
 */
public class LoadTestKVGenerator {

  /** A random number generator for determining value size */
  private Random randomForValueSize = new Random();

  private final int minValueSize;
  private final int maxValueSize;

  public LoadTestKVGenerator(int minValueSize, int maxValueSize) {
    if (minValueSize <= 0 || maxValueSize <= 0) {
      throw new IllegalArgumentException("Invalid min/max value sizes: " +
          minValueSize + ", " + maxValueSize);
    }
    this.minValueSize = minValueSize;
    this.maxValueSize = maxValueSize;
  }

  /**
   * Verifies that the given byte array is the same as what would be generated
   * for the given row key and qualifier. We are assuming that the value size
   * is correct, and only verify the actual bytes. However, if the min/max
   * value sizes are set sufficiently high, an accidental match should be
   * extremely improbable.
   */
  public static boolean verify(String rowKey, String qual, byte[] value) {
    byte[] expectedData = getValueForRowColumn(rowKey, qual, value.length);
    return Bytes.equals(expectedData, value);
  }

  /**
   * Converts the given key to string, and prefixes it with the MD5 hash of
   * the index's string representation.
   */
  public static String md5PrefixedKey(long key) {
    String stringKey = Long.toString(key);
    String md5hash = MD5Hash.getMD5AsHex(Bytes.toBytes(stringKey));

    // flip the key to randomize
    return md5hash + "-" + stringKey;
  }

  /**
   * Generates a value for the given key index and column qualifier. Size is
   * selected randomly in the configured range. The generated value depends
   * only on the combination of the key, qualifier, and the selected value
   * size. This allows to verify the actual value bytes when reading, as done
   * in {@link #verify(String, String, byte[])}.
   */
  public byte[] generateRandomSizeValue(long key, String qual) {
    String rowKey = md5PrefixedKey(key);
    int dataSize = minValueSize;
    if(minValueSize != maxValueSize){
      dataSize = minValueSize + randomForValueSize.nextInt(Math.abs(maxValueSize - minValueSize));
    }
    return getValueForRowColumn(rowKey, qual, dataSize);
  }

  /**
   * Generates random bytes of the given size for the given row and column
   * qualifier. The random seed is fully determined by these parameters.
   */
  private static byte[] getValueForRowColumn(String rowKey, String qual,
      int dataSize) {
    Random seededRandom = new Random(rowKey.hashCode() + qual.hashCode() +
        dataSize);
    byte[] randomBytes = new byte[dataSize];
    seededRandom.nextBytes(randomBytes);
    return randomBytes;
  }

}