#16 board : pagination service impl & test

board/src/main/java/com/example/board/service/PaginationService.java

@@ -0,0 +1,23 @@
+package com.example.board.service;
+
+import org.springframework.stereotype.Service;
+
+import java.util.List;
+import java.util.stream.IntStream;
+
+@Service
+public class PaginationService {
+
+    private static final int BAR_LENGTH = 5;
+
+    public List<Integer> getPaginationBarNumbers(int currentPageNumber, int totalPages) {
+        int startNumber = Math.max(currentPageNumber - (BAR_LENGTH / 2), 0);
+        int endNumber = Math.min(startNumber + BAR_LENGTH, totalPages);
+
+        return IntStream.range(startNumber, endNumber).boxed().toList();
+    }
+
+    public int currentBarLength() {
+        return BAR_LENGTH;
+    }
+}

board/src/test/java/com/example/board/service/PaginationServiceTest.java

@@ -0,0 +1,67 @@
+package com.example.board.service;
+
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+
+import java.util.List;
+import java.util.stream.Stream;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.params.provider.Arguments.arguments;
+
+@DisplayName("비지니스 로직 - 페이지네이션")
+@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.NONE, classes = PaginationService.class)
+class PaginationServiceTest {
+
+    private final PaginationService sut;
+
+
+    public PaginationServiceTest(@Autowired PaginationService paginationService) {
+        this.sut = paginationService;
+    }
+
+    @DisplayName("현재 페이지 번호와 총 페이지 수를 주면, 페이징 바 리스트를 만들어준다.")
+    @MethodSource
+    @ParameterizedTest(name = "[{index}] {0}, {1} => {2}")
+    void givenCurrentPageNumberAndTotalPages_whenCalculating_thenReturnsPaginationBarNumbers(int currentPageNumber, int totalPages, List<Integer> expected) {
+        // given
+
+        // when
+        List<Integer> actual = sut.getPaginationBarNumbers(currentPageNumber, totalPages);
+
+        // then
+        assertThat(actual).isEqualTo(expected);
+    }
+
+    static Stream<Arguments> givenCurrentPageNumberAndTotalPages_whenCalculating_thenReturnsPaginationBarNumbers() {
+        return Stream.of(
+                arguments(0, 13, List.of(0, 1, 2, 3, 4)),
+                arguments(1, 13, List.of(0, 1, 2, 3, 4)),
+                arguments(2, 13, List.of(0, 1, 2, 3, 4)),
+                arguments(3, 13, List.of(1, 2, 3, 4, 5)),
+                arguments(4, 13, List.of(2, 3, 4, 5, 6)),
+                arguments(5, 13, List.of(3, 4, 5, 6, 7)),
+                arguments(6, 13, List.of(4, 5, 6, 7, 8)),
+                arguments(10, 13, List.of(8, 9, 10, 11, 12)),
+                arguments(11, 13, List.of(9, 10, 11, 12)),
+                arguments(12, 13, List.of(10, 11, 12))
+        );
+    }
+
+    @DisplayName("현재 설정되어 있는 페이지네이션 바의 길이를 알려준다.")
+    @Test
+    void givenNothing_whenCalling_thenReturnsCurrentBarLength() {
+        // given
+
+        // when
+        int barLength = sut.currentBarLength();
+
+        // then
+        assertThat(barLength).isEqualTo(5);
+    }
+}