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Nuts'n'Bolts Utilities
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/*
 * Copyright (c) 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020 David Berkman
 *
 * This file is part of the SmallMind Code Project.
 *
 * The SmallMind Code Project is free software, you can redistribute
 * it and/or modify it under either, at your discretion...
 *
 * 1) The terms of GNU Affero General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or (at
 * your option) any later version.
 *
 * ...or...
 *
 * 2) The terms of the Apache License, Version 2.0.
 *
 * The SmallMind Code Project 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 or Apache License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * and the Apache License along with the SmallMind Code Project. If not, see
 *  or .
 *
 * Additional permission under the GNU Affero GPL version 3 section 7
 * ------------------------------------------------------------------
 * If you modify this Program, or any covered work, by linking or
 * combining it with other code, such other code is not for that reason
 * alone subject to any of the requirements of the GNU Affero GPL
 * version 3.
 */
package org.smallmind.nutsnbolts.util;

import java.lang.management.ManagementFactory;
import java.math.BigInteger;
import java.security.SecureRandom;
import java.util.Arrays;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.StampedLock;
import org.smallmind.nutsnbolts.security.HexCodec;

public class SnowflakeId implements Comparable {

  private static final StampedLock LOCK = new StampedLock();

  private static final int[] DOT_OFFSET_0 = {0, 0, 0};
  private static final int[] DOT_OFFSET_1 = {0, 0, 0};
  private static final int[] DOT_OFFSET_2 = {0, 1, 0};
  private static final int[] DOT_OFFSET_3 = {0, 1, 1};

  private static final int CODE_TEMPLATE_BITS = 5;
  private static final String CODE_TEMPLATE = "ABCDEFGHIJKMNPQRSTUVWXYZ23456789";

  private static final int COMPACT_CODE_TEMPLATE_BITS = 6;
  private static final String COMPACT_CODE_TEMPLATE = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890$*";

  private static final int[] POWER_ARRAY = {1, 2, 4, 8, 16, 32, 64, 128};

  private static final SecureRandom RANDOM = new SecureRandom(Bytes.getBytes(System.currentTimeMillis()));

  private static final byte[] MAC_BYTES = createMachineIdentifier();
  private static final byte[] JVM_BYTES = createJVMProcessIdentifier();
  private static final AtomicInteger COUNT = new AtomicInteger(Short.MIN_VALUE);
  private static long TIME = System.currentTimeMillis();
  private final byte[] uniqueArray;

  public SnowflakeId () {

    uniqueArray = generateByteArray();
  }

  public SnowflakeId (byte[] uniqueArray) {

    this.uniqueArray = uniqueArray;
  }

  public static int byteSize () {

    return 18;
  }

  public static SnowflakeId newInstance () {

    return new SnowflakeId();
  }

  private static byte[] createMachineIdentifier () {

    byte[] macBytes = new byte[6];

    try {

      byte[] macAddress = MacAddress.getBytes();

      System.arraycopy(macAddress, 0, macBytes, 0, 6);
    } catch (Exception exception) {
      RANDOM.nextBytes(macBytes);
    }

    return macBytes;
  }

  private static byte[] createJVMProcessIdentifier () {

    try {

      String processName = ManagementFactory.getRuntimeMXBean().getName();
      int atSignPos;

      if ((atSignPos = processName.indexOf('@')) >= 0) {

        return Bytes.getBytes((short)Integer.parseInt(processName.substring(0, atSignPos)));
      } else {

        return Bytes.getBytes((short)processName.hashCode());
      }
    } catch (Throwable t) {

      byte[] jvmBytes = new byte[2];

      ThreadLocalRandom.current().nextBytes(jvmBytes);

      return jvmBytes;
    }
  }

  private byte[] generateByteArray () {

    byte[] bytes = new byte[18];
    long currentTime = 0;
    int currentCount;
    long stamp;

    do {
      stamp = LOCK.readLock();
      try {
        if ((currentCount = COUNT.incrementAndGet()) < Short.MAX_VALUE) {
          currentTime = TIME;
        } else if (currentCount == Short.MAX_VALUE) {

          long upgradedStamp;

          if ((upgradedStamp = LOCK.tryConvertToWriteLock(stamp)) == 0L) {
            LOCK.unlock(stamp);
            upgradedStamp = LOCK.writeLock();
          }

          stamp = upgradedStamp;
          TIME = currentTime = Math.max(TIME + 1, System.currentTimeMillis());
          COUNT.set(currentCount = Short.MIN_VALUE);
        }
      } finally {
        LOCK.unlock(stamp);
      }
    } while (currentCount > Short.MAX_VALUE);

    if (currentTime == 0) {
      throw new IllegalStateException("Current time value should never be '0'");
    }

    System.arraycopy(Bytes.getBytes(currentTime), 0, bytes, 0, 8);
    System.arraycopy(MAC_BYTES, 0, bytes, 8, 6);
    System.arraycopy(JVM_BYTES, 0, bytes, 14, 2);
    System.arraycopy(Bytes.getBytes((short)currentCount), 0, bytes, 16, 2);

    return bytes;
  }

  public byte[] asByteArray () {

    return uniqueArray;
  }

  public BigInteger generateBigInteger () {

    return new BigInteger(uniqueArray);
  }

  public String generateHexEncoding () {

    return HexCodec.hexEncode(uniqueArray);
  }

  public String generateCompactString () {

    return generateTemplateString(COMPACT_CODE_TEMPLATE, COMPACT_CODE_TEMPLATE_BITS).toString();
  }

  public String generateDottedString () {

    StringBuilder dottedIdBuilder = generateTemplateString(CODE_TEMPLATE, CODE_TEMPLATE_BITS);
    int dashSize;

    dashSize = dottedIdBuilder.length() / 4;
    switch (dottedIdBuilder.length() % 4) {
      case 0:
        return insertDots(dottedIdBuilder, DOT_OFFSET_0, dashSize);
      case 1:
        return insertDots(dottedIdBuilder, DOT_OFFSET_1, dashSize);
      case 2:
        return insertDots(dottedIdBuilder, DOT_OFFSET_2, dashSize);
      default:
        return insertDots(dottedIdBuilder, DOT_OFFSET_3, dashSize);
    }
  }

  private String insertDots (StringBuilder dottedIdBuilder, int[] offsets, int dashSize) {

    for (int count = 0; count < offsets.length; count++) {
      dottedIdBuilder.insert((dashSize * (count + 1)) + count + offsets[count], '.');
    }

    return dottedIdBuilder.toString();
  }

  private StringBuilder generateTemplateString (String template, int templateBits) {

    StringBuilder uniqueIdBuilder = new StringBuilder();

    int codeIndex = 0;
    int codeValue = 0;

    for (byte codeByte : uniqueArray) {
      for (int count = 0; count < 8; count++) {
        if ((codeByte & POWER_ARRAY[count]) != 0) {
          codeValue += POWER_ARRAY[codeIndex];
        }

        if (++codeIndex == templateBits) {
          uniqueIdBuilder.append(template.charAt(codeValue));
          codeIndex = 0;
          codeValue = 0;
        }
      }
    }

    if (codeIndex > 0) {
      uniqueIdBuilder.append(CODE_TEMPLATE.charAt(codeValue));
    }

    return uniqueIdBuilder;
  }

  @Override
  public int hashCode () {

    return Arrays.hashCode(uniqueArray);
  }

  @Override
  public boolean equals (Object obj) {

    return (obj instanceof SnowflakeId) && Arrays.equals(uniqueArray, ((SnowflakeId)obj).asByteArray());
  }

  public int compareTo (SnowflakeId snowflakeId) {

    int comparison;

    if ((comparison = compareTimeBytes(snowflakeId)) == 0) {
      if ((comparison = compareCountBytes(snowflakeId)) == 0) {
        if ((comparison = compareMacBytes(snowflakeId)) == 0) {

          return compareJVMBytes(snowflakeId);
        }
      }
    }

    return comparison;
  }

  private int compareMacBytes (SnowflakeId snowflakeId) {

    int comparison;

    for (int count = 8; count < 14; count++) {
      if ((comparison = this.asByteArray()[count] - snowflakeId.asByteArray()[count]) != 0) {

        return comparison;
      }
    }

    return 0;
  }

  private int compareJVMBytes (SnowflakeId snowflakeId) {

    int comparison;

    for (int count = 14; count < 16; count++) {
      if ((comparison = this.asByteArray()[count] - snowflakeId.asByteArray()[count]) != 0) {

        return comparison;
      }
    }

    return 0;
  }

  private int compareTimeBytes (SnowflakeId snowflakeId) {

    return Long.compare(Bytes.getLong(Arrays.copyOfRange(this.asByteArray(), 0, 8)), Bytes.getLong(Arrays.copyOfRange(snowflakeId.asByteArray(), 0, 8)));
  }

  private int compareCountBytes (SnowflakeId snowflakeId) {

    return Short.compare(Bytes.getShort(Arrays.copyOfRange(this.asByteArray(), 16, 18)), Bytes.getShort(Arrays.copyOfRange(snowflakeId.asByteArray(), 16, 18)));
  }
}