package org.codekata;

public class StringCalculator {

    private static final String NEGATIVE_NUMBER_EXCEPTION_MSG = "negatives not allowed - ";

    private static final String DEFAULT_SEPARATOR = ",";

    private static final String OPTIONAL_DELIMITER = "//";

    public int add(String numbers) {
        if (numbersIsBlank(numbers))
            return 0;
        handleNegativeNumbers(numbers);
        if (hasOptionalDelimiter(numbers)) {
            return handleSumOfMoreThanOneNumber(extractNumberPart(numbers),
                    extractDelimiter(numbers));
        }
        if (hasMoreThanOneNumber(numbers)) {
            return handleSumOfMoreThanOneNumber(numbers, DEFAULT_SEPARATOR);
        }
        return handleOneNumber(numbers);
    }

    private void handleNegativeNumbers(String numbers) {
        if (hasMoreThanOneNumber(numbers)) {
            handleMoreThanOneNegativeNumber(numbers);
        } else {
            handleOneNegativeNumber(numbers);
        }
    }

    private void handleOneNegativeNumber(String numbers) {
        if (numberHasHypen(numbers)) {
            throwNegativeNumberException(numbers);
        }
    }

    private void throwNegativeNumberException(String numbers) {
        throw new IllegalArgumentException(NEGATIVE_NUMBER_EXCEPTION_MSG
                + numbers);
    }

    private void handleMoreThanOneNegativeNumber(String numbers) {
        StringBuffer negativeNumbers = new StringBuffer();
        for (String num : numbers.split(DEFAULT_SEPARATOR)) {
            if (numberHasHypen(num)) {
                negativeNumbers.append(num).append(" ");
            }
        }
        if (negativeNumbers.length() > 0) {
            throwNegativeNumberException(negativeNumbers.toString());
        }
    }

    private boolean numberHasHypen(String numbers) {
        return numbers.contains("-");
    }

    private boolean hasOptionalDelimiter(String numbers) {
        return numbers.startsWith(OPTIONAL_DELIMITER);
    }

    private String extractDelimiter(String numbers) {
        return numbers.substring(2, 3);
    }

    private String extractNumberPart(String numbers) {
        return numbers.substring(4, numbers.length());
    }

    private int handleSumOfMoreThanOneNumber(String numbers, String delimiter) {
        int sum = 0;
        numbers = replaceNewLineToDelimiter(numbers, delimiter);
        for (String num : numbers.split(delimiter)) {
            sum += handleOneNumber(num);
        }
        return sum;
    }

    private String replaceNewLineToDelimiter(String numbers, String delimiter) {
        return numbers.replaceAll("\n", delimiter);
    }

    private boolean hasMoreThanOneNumber(String numbers) {
        return numbers.contains(DEFAULT_SEPARATOR);
    }

    private int handleOneNumber(String numbers) {
        return Integer.parseInt(numbers);
    }

    private boolean numbersIsBlank(String numbers) {
        return "".equals(numbers);
    }

}