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A set of utilities for classes of the java.lang and the java.util packages.
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/*
 * Copyright (C) 2011-2021 Objectos Software LTDA.
 *
 * This file is part of the ObjectosComuns project.
 *
 * ObjectosComuns is free software: you can redistribute it and/or modify
 * it under the terms of the 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.
 *
 * ObjectosComuns 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with ObjectosComuns.  If not, see .
 */
package br.com.objectos.lang;

import static br.com.objectos.lang.Lang.checkArgument;
import static br.com.objectos.lang.Lang.checkNotNull;

import java.security.SecureRandom;
import java.util.Random;

final class RandomImpl {

  static final String DEFAULT_DICTIONARY
      = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

  static final RandomImpl INSTANCE = new RandomImpl();

  private static final char[] DEFAULT_DICTIONARY_CHARS = DEFAULT_DICTIONARY.toCharArray();

  private final Random delegate = new SecureRandom();

  private RandomImpl() {}

  public final byte[] randomByteArray(int length) {
    checkArgument(length >= 0, "length has to be >= 0");

    switch (length) {
      case 0:
        return Lang.emptyByteArray();
      default:
        byte[] array;
        array = new byte[length];

        randomBytes(array);

        return array;
    }
  }

  public final void randomBytes(byte[] bytes) {
    checkNotNull(bytes, "bytes == null");

    delegate.nextBytes(bytes);
  }

  public final double randomDouble() {
    return delegate.nextDouble();
  }

  public final int randomInt() {
    return delegate.nextInt();
  }

  public final int randomInt(int bound) {
    return delegate.nextInt(bound);
  }

  public final String randomString(int length) {
    checkArgument(length > 0, "length has to be > 0");

    return randomString0(DEFAULT_DICTIONARY_CHARS, length);
  }

  private String randomString0(char[] chars, int length) {
    char[] result;
    result = new char[length];

    int index;
    index = 0;

    int fullIntCount;
    fullIntCount = length / 4;

    for (int i = 0; i < fullIntCount; i++) {
      int value;
      value = delegate.nextInt();

      result[index++] = chars[((value >> 12) & 0xFF) % chars.length];

      result[index++] = chars[((value >> 8) & 0xFF) % chars.length];

      result[index++] = chars[((value >> 4) & 0xFF) % chars.length];

      result[index++] = chars[(value & 0xFF) % chars.length];
    }

    int lastIntCount;
    lastIntCount = length % 4;

    if (lastIntCount > 0) {
      int value;
      value = delegate.nextInt();

      switch (lastIntCount) {
        case 3:
          result[index + 2] = chars[((value >> 4) & 0xFF) % chars.length];
          // fall through
        case 2:
          result[index + 1] = chars[((value >> 8) & 0xFF) % chars.length];
          // fall through
        case 1:
          result[index + 0] = chars[((value >> 12) & 0xFF) % chars.length];
          break;
        default:
          throw new AssertionError("Should not happen");
      }
    }

    return new String(result);
  }

}