import org.apache.commons.lang.StringUtils;
import org.apache.commons.lang.math.NumberUtils;

import java.util.regex.Pattern;

public class PersonalCode {

  /** Each Estonian personal code must match this pattern */
  private static final Pattern NUMBER_PATTERN = Pattern.compile("^\\d{11}$");

  /**
     * Checks if is valid.
     *
     * @param number
     *            the number
     *
     * @return true, if is valid
     */
  public static boolean isValid(final String number) {
    return StringUtils.isNotBlank(number)
           && NUMBER_PATTERN.matcher(number).matches()
           && calculateChecksum(number) == NumberUtils.toInt(number.substring(10));
  }


  /**
     * Calculates checksum number for a given personal code. By the general rule
     * calculated checksum must be the same as the last digit of the given
     * personal code
     *
     * @param number
     *            personal code as string
     *
     * @return registration number checksum
     */
  private static int calculateChecksum(String number) {
    int remainder = calculateWeightRemainder(number, new int[]{1, 2, 3, 4, 5, 6, 7, 8, 9, 1});
    if (remainder < 10)
      return remainder;
    if (remainder == 10)
      remainder = calculateWeightRemainder(number, new int[]{3, 4, 5, 6, 7, 8, 9, 1, 2, 3});
    return remainder < 10 ? remainder : 0;
  }

  /**
     * Calculate weight remainder.
     *
     * @param number
     *            the number
     * @param weights
     *            the weights
     *
     * @return the int
     */
  private static int calculateWeightRemainder(final String number, final int[] weights) {
    int sum = 0;
    for (int i = 0; i < weights.length; i++) {//sum up all weights
      sum += NumberUtils.toInt(number.substring(i, i + 1)) * weights[i];
    }
    return sum % 11;//return division remainder
  }

}