public final class Ints {
  private Ints() {}

  public static boolean isInt(String value) {
    return isInt(value, DEFAULT_RADIX);
  }

  public static boolean isInt(String value, int radix) {
    if (canNotBeValid(value, radix)) {
      return false;
    }
    int index = findFirstValidNonSignCharacter(value);
    if (index == FIRST_CHARACTER_IS_INVALID) {
      return false;
    }
    return hasValidIntDigits(value, index, radix);
  }

  private static final int MIN_SUPPORTED_RADIX = 2;
  private static final int MAX_SUPPORTED_RADIX = 36;

  private static boolean isSupportedRadix(int radix) {
    return radix >= MIN_SUPPORTED_RADIX && radix <= MAX_SUPPORTED_RADIX;
  }

  private static final int DEFAULT_RADIX = 10; // decimal

  private static boolean isNullOrEmpty(String value) {
    return value == null || value.isEmpty();
  }

  private static boolean canNotBeValid(String value, int radix) {
    return isNullOrEmpty(value) || !isSupportedRadix(radix);
  }

  private static boolean hasValidIntDigits(String value, int index, int radix) {
    int length = value.length();
    while (index < length) {
      int digit = Character.digit(value.charAt(index++), radix);
      if (digit < 0 || digit > radix) {
        return false;
      }
    }
    return true;
  }

  private static final int FIRST_CHARACTER_IS_INVALID = -1;

  private static int findFirstValidNonSignCharacter(String value) {
    char firstCharacter = value.charAt(0);
    if (firstCharacter < '0') {
      switch (firstCharacter) {
        case '-':
          return 1;
        case '+':
          return value.length() > 1 ? 1 : FIRST_CHARACTER_IS_INVALID;
        default:
          return FIRST_CHARACTER_IS_INVALID;
      }
    }
    return firstCharacter == '0'
      ? findFirstValidDigitOfSpecialInt(value)
      : 0;
  }

  // Special strings are strings that contain a radix sign. Like: 0x0, 0b0, etc
  private static final int MIN_SPECIAL_STRING_LENGTH = 3;
  private static final int SPECIAL_STRING_RADIX_SIGN_INDEX = 1;
  private static final int SPECIAL_STRING_FIRST_DIGIT_INDEX = 2;

  private static int findFirstValidDigitOfSpecialInt(String value) {
    if (value.length() < MIN_SPECIAL_STRING_LENGTH) {
      return FIRST_CHARACTER_IS_INVALID;
    }
    switch (value.charAt(SPECIAL_STRING_RADIX_SIGN_INDEX)) {
      case 'x':
      case 'X':
      case 'b':
      case 'B':
        return SPECIAL_STRING_FIRST_DIGIT_INDEX;
    }
    return FIRST_CHARACTER_IS_INVALID;
  }
}