Validate a South African ID number

RsaIdValidator.java

import java.time.YearMonth;
import java.util.Optional;
import java.util.regex.Pattern;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;

public class RsaIdValidator {
    
    public static boolean validateRsaId(String id, boolean validateGender, boolean isMale) {
        return Optional.ofNullable(id)
                .filter(i -> Pattern.matches("^\\d{13}", i))
                .map(i -> Stream.of(i.split("")).map(Integer::parseInt).collect(Collectors.toList()))
                // Validate date of birth
                .filter(digits -> {
                    int month = digits.get(2) * 10 + digits.get(3);
                    if (month > 12 || month < 1) {
                        return false;
                    }

                    YearMonth now = YearMonth.now();
                    int yearNow = now.getYear();
                    int monthNow = now.getMonthValue();
                    int century = yearNow / 100;
                    yearNow = (yearNow % 10) + ((yearNow / 10) % 10) * 10; // If 2019, get the 19
                    int year = digits.get(0) * 10 + digits.get(1);

                    // 18 -> 2018, 20 -> 1920, 19 -> 2019 if month < nowMonth given calculated in 2019
                    year += yearNow > year || (yearNow == year && month <= monthNow)
                            ? century*100
                            : (century - 1)* 100;

                    int day = digits.get(4)*10 + digits.get(5);
                    return YearMonth.of(year, month).lengthOfMonth() >= day;
                })
                .filter(digits -> !validateGender || (isMale && digits.get(6) < 5))
                .filter(digits -> digits.get(10) == 0 || digits.get(10) == 1) // 11th digit must be either 0 (RSA citizen) or 1 (Permanent resident)
                // Start calculating the Luhn check number
                .map(digits ->
                        IntStream.range(0, digits.size()/2)
                            .map(i -> i * 2 + 1 ) // Get even indexes if arrays starts at 1
                            .map(digits::get)
                            .map(i -> i * 2) // Even indexes x 2
                            .map(i -> i % 10 + ((i / 10) % 10)) // Sum the characters
                            .reduce(0, Integer::sum) +
                        IntStream.range(0, digits.size()/2)
                            .map(i -> i * 2) // Get odd indexes
                            .map(digits::get)
                            .map(i -> i % 10 + ((i / 10) % 10))
                            .reduce(0, Integer::sum)
                )
                .map(i -> (10 - (i % 10)) % 10) // Luhn number here
                .map(i -> Integer.parseInt(id.substring(id.length() - 2)) % 10 == i) // Compare the calculated Luhn check with the last char of the number
                .orElse(false);
    }
}