/*
    * Copyright (C) 2019 uwe
    *
    * This program is free software: you can redistribute it and/or modify
    * it under the terms of the GNU General Public License as published by
    * the Free Software Foundation, either version 3 of the License, or
    * (at your option) any later version.
    *
    * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
   */
  package org.sw4j.sample.memory.heap;
  
  import java.security.MessageDigest;
  import java.security.NoSuchAlgorithmException;
  import java.util.Random;
  import java.util.logging.Logger;
  
  /**
   *
   * @author Uwe Plonus &lt;u.plonus@gmail.com&gt;
   */
  public class Allocator {
          //implements Runnable {
  
      private static final int kiByte = 1024;
  
      private static final Logger logger = Logger.getLogger(Allocator.class.getName());
  
      private byte[] data;
  
      private byte[] digest;
  
      private final Random rand = new Random();
  
      /**
       * Creates a new allocator and reserves {@code blocks} 1 KiB blocks.
       *
       * @param blocks the number of blocks to reserve.
       */
      public Allocator(int blocks) {
          data = new byte[blocks * kiByte];
      }
  
      public void calculateHash() throws NoSuchAlgorithmException {
          byte[] filler = new byte[kiByte];
          for (int i = 0; i < data.length / kiByte; i++) {
              rand.nextBytes(filler);
              System.arraycopy(filler, 0, data, kiByte * i, kiByte);
          }
          String digestAlgorithm = "SHA3-512";
          String javaVersion = System.getProperty("java.specification.version");
          try {
              double version = Double.parseDouble(javaVersion);
              if (version < 9.0d) {
                  logger.config("Pre Java 9 VM detected.");
                  digestAlgorithm = "SHA-512";
              } else {
                  logger.config("Post Java 8 VM detected.");
              }
          } catch (NumberFormatException nfex) {
              logger.config(String.format("Unknown Java version: %s.", javaVersion));
              digestAlgorithm = "SHA-512";
          }
          logger.config(String.format("Using hash algorithm %s", digestAlgorithm));
          MessageDigest digester = MessageDigest.getInstance(digestAlgorithm);
          digest = digester.digest(data);
      }
  
      public String getHash() {
          StringBuilder sb = new StringBuilder();
          for (int i = 0; i < digest.length; i++) {
              sb.append(String.format("%02x", digest[i]));
          }
          return sb.toString();
      }
  
  //    @Override
  //    public void run() {
  //        data = null;
  //    }
  
  }