tasks2/StringCalculator/src/main/java/pl/dmcs/Calculator.java

package pl.dmcs;

import java.util.ArrayList;
import java.util.List;
import java.util.regex.Pattern;

public class Calculator {
    public int add(String numbers) {
        if (numbers == null || numbers.isEmpty()) {
            return 0;
        }

        String delimiter = "[,\n]";
        if (numbers.startsWith("//")) {
            int delimiterIndex = numbers.indexOf("\n");
            delimiter = Pattern.quote(numbers.substring(2, delimiterIndex));
            numbers = numbers.substring(delimiterIndex + 1);
        }

        String[] numArray = numbers.split(delimiter);
        int sum = 0;
        List<Integer> negativeNumbers = new ArrayList<>();
        for (String num : numArray) {
            if (!num.trim().isEmpty()) {
                int number = Integer.parseInt(num.trim());
                if (number < 0) {
                    negativeNumbers.add(number);
                }
                sum += number;
            }
        }

        if (!negativeNumbers.isEmpty()) {
            throw new NegativeNumberException(negativeNumbers);
        }

        return sum;
    }
}