자동차 경주: 2단계 - 문자열 덧셈 계산기

src/main/java/step2/CalculatorMatcher.java

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+package step2;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+public class CalculatorMatcher {
+
+    private static final String CUSTOM_DELIMITER_REGEX = "//(.)\n(.*)";
+
+    private static final Pattern CUSTOM_DELIMITER_PATTERN = Pattern.compile(CUSTOM_DELIMITER_REGEX);
+
+    public static Matcher getCustomMatcher(String input) {
+        return CUSTOM_DELIMITER_PATTERN.matcher(input);
+    }
+}

src/main/java/step2/StringAddCalculator.java

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+package step2;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.regex.Matcher;
+import java.util.stream.Collectors;
+
+public class StringAddCalculator {
+
+    public static final List<String> DEFAULT_DELIMITER = List.of(",", ":");
+    private static final int GROUP_INDEX_DELIMITER = 1;
+    private static final int GROUP_INDEX_NUMBERS = 2;
+
+    /**
+     * 문자열 덧셈 계산기
+     *
+     * @param input 입력값
+     * @return 계산 결과
+     */
+    public static int calculate(String input) {
+        if (isNullOrBlack(input)) {
+            return 0;
+        }
+
+        return sum(toInts(split(input)));
+    }
+
+    private static boolean isNullOrBlack(String input) {
+        return input == null || input.isBlank();
+    }
+
+    private static List<String> split(String input) {
+        Matcher customMatcher = CalculatorMatcher.getCustomMatcher(input);
+
+        if (customMatcher.find()) {
+            return splitWithCustomDelimiter(customMatcher);
+        }
+        return List.of(input.split(defaultDelimiterRegex()));
+    }
+
+    private static List<String> splitWithCustomDelimiter(Matcher customMatcher) {
+        return Arrays.stream(customMatcher.group(GROUP_INDEX_NUMBERS)
+                        .split(customMatcher.group(GROUP_INDEX_DELIMITER)))
+                .collect(Collectors.toList());
+    }
+
+    public static String defaultDelimiterRegex() {
+        return "[" + String.join("", DEFAULT_DELIMITER) + "]";
+    }
+
+    private static List<Integer> toInts(List<String> values) {
+        return values.stream()
+                .map(value -> toInt(value))
+                .collect(Collectors.toList());
+    }
+
+    private static int toInt(String value) {
+        int number = Integer.parseInt(value);
+        checkNegativeNumber(number);
+        return number;
+    }
+
+    private static void checkNegativeNumber(int number) {
+        if (number < 0) {
+            throw new RuntimeException(String.format("음수(%s)는 사용할 수 없습니다.", number));
+        }
+    }
+
+    private static int sum(List<Integer> values) {
+        return values.stream()
+                .mapToInt(Integer::intValue)
+                .sum();
+    }
+}

src/test/java/step2/StringAddCalculatorTest.java

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+package step2;
+
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.NullAndEmptySource;
+import org.junit.jupiter.params.provider.ValueSource;
+
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static step2.StringAddCalculator.calculate;
+
+public class StringAddCalculatorTest {
+
+    @ParameterizedTest
+    @DisplayName("숫자 하나를 문자열로 입력할 경우 해당 숫자를 반환한다.")
+    @ValueSource(strings = {"1", "2", "3"})
+    public void calculate_숫자하나(String input) throws Exception {
+        int result = calculate(input);
+        assertThat(result).isEqualTo(Integer.parseInt(input));
+    }
+
+    @ParameterizedTest
+    @NullAndEmptySource
+    @DisplayName("null 또는 빈문자를 입력할 경우 0을 반환해야 한다.")
+    public void calculate_null_또는_빈문자(String input) {
+        assertThat(calculate(input)).isEqualTo(0);
+    }
+
+    @ParameterizedTest
+    @DisplayName("숫자 두 개를 콤마(,) 구분자로 입력할 경우 두 숫자의 합을 반환한다.")
+    @ValueSource(strings = {"1,2", "1,2,"})
+    public void calculate_쉼표구분자(String input) throws Exception {
+        int result = calculate(input);
+        assertThat(result).isEqualTo(3);
+    }
+
+    @Test
+    @DisplayName("구분자는 콤마(,)와 콜론(:)을 사용할 수 있다.")
+    public void calculate_쉼표_또는_콜론_구분자() throws Exception {
+        int result = calculate("1,2:3");
+        assertThat(result).isEqualTo(6);
+    }
+
+    @ParameterizedTest
+    @DisplayName("구분자는 //와 /n 문자를 이용해 커스텀 구분자를 지정할 수 있다.")
+    @ValueSource(strings = {";", ":"})
+    public void calculate_custom_구분자(String delimiter) throws Exception {
+        List<String> inputNumbers = List.of("1", "2", "3");
+        String customDelimiter = "//" + delimiter + "\n";
+
+        int result = calculate(customDelimiter + String.join(delimiter, inputNumbers));
+        assertThat(result).isEqualTo(
+                inputNumbers.stream()
+                .mapToInt(Integer::parseInt)
+                .sum()
+        );
+    }
+
+    @ParameterizedTest
+    @DisplayName("음수를 전달할 경우 예외가 발생한다.")
+    @ValueSource(strings = {"-1", "1,-2,3"})
+    public void calculate_negative(String input) throws Exception {
+        assertThatThrownBy(() -> calculate(input))
+                .isInstanceOf(RuntimeException.class);
+    }
+}