feat: 즐겨찾기 기능을 구현한다.

src/main/java/kr/allcll/seatfinder/exception/AllcllErrorCode.java

@@ -3,7 +3,9 @@
 public enum AllcllErrorCode {
 
     PIN_LIMIT_EXCEEDED("이미 %d개의 핀을 등록했습니다."),
+    STAR_LIMIT_EXCEEDED("이미 %d개의 즐겨찾기를 등록했습니다."),
     DUPLICATE_PIN("%s은(는) 이미 핀 등록된 과목입니다."),
+    DUPLICATE_STAR("%s은(는) 이미 핀 등록된 과목입니다."),
     PIN_SUBJECT_MISMATCH("핀에 등록된 과목이 아닙니다."),
     TOKEN_NOT_FOUND("쿠키에 토큰이 존재하지 않습니다."),
     SUBJECT_NOT_FOUND("존재하지 않는 과목 입니다.");

src/main/java/kr/allcll/seatfinder/star/Star.java

@@ -0,0 +1,37 @@
+package kr.allcll.seatfinder.star;
+
+import jakarta.persistence.Column;
+import jakarta.persistence.Entity;
+import jakarta.persistence.FetchType;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.GenerationType;
+import jakarta.persistence.Id;
+import jakarta.persistence.JoinColumn;
+import jakarta.persistence.ManyToOne;
+import jakarta.persistence.Table;
+import kr.allcll.seatfinder.subject.Subject;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+
+@Table(name = "star")
+@Entity
+@Getter
+@NoArgsConstructor
+public class Star {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    @Column(name = "token")
+    private String token;
+
+    @ManyToOne(fetch = FetchType.LAZY, optional = false)
+    @JoinColumn(name = "subject_id", nullable = false)
+    private Subject subject;
+
+    public Star(String token, Subject subject) {
+        this.token = token;
+        this.subject = subject;
+    }
+}

src/main/java/kr/allcll/seatfinder/star/StarApi.java

@@ -0,0 +1,21 @@
+package kr.allcll.seatfinder.star;
+
+import kr.allcll.seatfinder.ThreadLocalHolder;
+import lombok.RequiredArgsConstructor;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestParam;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+@RequiredArgsConstructor
+public class StarApi {
+
+    private final StarService starService;
+
+    @PostMapping("/api/stars")
+    ResponseEntity<Void> addStarOnSubject(@RequestParam Long subjectId) {
+        starService.addStarOnSubject(subjectId, ThreadLocalHolder.SHARED_TOKEN.get());
+        return ResponseEntity.ok().build();
+    }
+}

src/main/java/kr/allcll/seatfinder/star/StarRepository.java

@@ -0,0 +1,12 @@
+package kr.allcll.seatfinder.star;
+
+import java.util.List;
+import kr.allcll.seatfinder.subject.Subject;
+import org.springframework.data.jpa.repository.JpaRepository;
+
+public interface StarRepository extends JpaRepository<Star, Long> {
+
+    boolean existsBySubjectAndToken(Subject subject, String token);
+
+    List<Star> findAllByToken(String token);
+}

src/main/java/kr/allcll/seatfinder/star/StarService.java

@@ -0,0 +1,39 @@
+package kr.allcll.seatfinder.star;
+
+import java.util.List;
+import kr.allcll.seatfinder.exception.AllcllErrorCode;
+import kr.allcll.seatfinder.exception.AllcllException;
+import kr.allcll.seatfinder.subject.Subject;
+import kr.allcll.seatfinder.subject.SubjectRepository;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@Service
+@Transactional(readOnly = true)
+@RequiredArgsConstructor
+public class StarService {
+
+    private static final int MAX_STAR_NUMBER = 10;
+
+    private final StarRepository starRepository;
+    private final SubjectRepository subjectRepository;
+
+    @Transactional
+    public void addStarOnSubject(Long subjectId, String token) {
+        List<Star> starsByToken = starRepository.findAllByToken(token);
+        Subject subject = subjectRepository.findById(subjectId)
+            .orElseThrow(() -> new AllcllException(AllcllErrorCode.SUBJECT_NOT_FOUND));
+        validateCanAddStar(starsByToken, subject, token);
+        starRepository.save(new Star(token, subject));
+    }
+
+    private void validateCanAddStar(List<Star> userStars, Subject subject, String token) {
+        if (userStars.size() >= MAX_STAR_NUMBER) {
+            throw new AllcllException(AllcllErrorCode.STAR_LIMIT_EXCEEDED, MAX_STAR_NUMBER);
+        }
+        if (starRepository.existsBySubjectAndToken(subject, token)) {
+            throw new AllcllException(AllcllErrorCode.DUPLICATE_STAR, subject.getCuriNm());
+        }
+    }
+}

src/test/java/kr/allcll/seatfinder/star/StarServiceTest.java

@@ -0,0 +1,95 @@
+package kr.allcll.seatfinder.star;
+
+import static kr.allcll.seatfinder.support.fixture.SubjectFixture.createSubject;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+import java.util.List;
+import kr.allcll.seatfinder.exception.AllcllErrorCode;
+import kr.allcll.seatfinder.exception.AllcllException;
+import kr.allcll.seatfinder.subject.Subject;
+import kr.allcll.seatfinder.subject.SubjectRepository;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
+
+@SpringBootTest(webEnvironment = WebEnvironment.NONE)
+class StarServiceTest {
+
+    private static final int MAX_STAR_NUMBER = 10;
+    private static final String TOKEN = "token";
+
+    @Autowired
+    private StarService starService;
+
+    @Autowired
+    private SubjectRepository subjectRepository;
+
+    @Autowired
+    private StarRepository starRepository;
+
+    @BeforeEach
+    void setUp() {
+        starRepository.deleteAllInBatch();
+        subjectRepository.deleteAllInBatch();
+    }
+
+    @Test
+    @DisplayName("즐겨찾기 5개 미만일 경우 정상 등록을 검증한다.")
+    void addStarOnProject() {
+        // given
+        Subject subjectA = createSubject("컴퓨터구조", "003278", "001", "김보예");
+        subjectRepository.save(subjectA);
+        starService.addStarOnSubject(subjectA.getId(), TOKEN);
+
+        // when
+        List<Star> result = starRepository.findAllByToken(TOKEN);
+
+        // then
+        assertThat(result).hasSize(1);
+    }
+
+    @Test
+    @DisplayName("즐겨찾기가 5개 이상일 경우 예외를 검증한다.")
+    void canNotAddStarOnSubject() {
+        // given
+        Subject subjectA = createSubject("컴퓨터구조", "003278", "001", "김보예");
+        Subject subjectB = createSubject("운영체제", "003279", "001", "김수민");
+        Subject subjectC = createSubject("자료구조", "003280", "001", "김봉케");
+        Subject subjectD = createSubject("알고리즘", "003281", "001", "오현지");
+        Subject subjectE = createSubject("컴퓨터구조", "003278", "002", "전유채");
+        Subject overCountSubject = createSubject("컴퓨터구조", "003278", "002", "전유채");
+        subjectRepository.saveAll(List.of(subjectA, subjectB, subjectC, subjectD, subjectE, overCountSubject));
+        starRepository.saveAll(
+            List.of(
+                new Star(TOKEN, subjectA),
+                new Star(TOKEN, subjectB),
+                new Star(TOKEN, subjectC),
+                new Star(TOKEN, subjectD),
+                new Star(TOKEN, subjectE))
+        );
+
+        // when, then
+        assertThatThrownBy(() -> starService.addStarOnSubject(overCountSubject.getId(), TOKEN))
+            .isInstanceOf(AllcllException.class)
+            .hasMessageContaining(String.format(AllcllErrorCode.STAR_LIMIT_EXCEEDED.getMessage(), MAX_STAR_NUMBER));
+    }
+
+    @Test
+    @DisplayName("이미 즐겨찾기 등록된 과목일 경우 예외를 검증한다.")
+    void alreadyExistStarSubject() {
+        // given
+        Subject subject = createSubject("컴퓨터구조", "003278", "001", "김보예");
+        subjectRepository.save(subject);
+        starRepository.save(new Star(TOKEN, subject));
+        String expectExceptionMessage = new AllcllException(AllcllErrorCode.DUPLICATE_STAR, "컴퓨터구조").getMessage();
+
+        // when, then
+        assertThatThrownBy(() -> starService.addStarOnSubject(subject.getId(), TOKEN))
+            .isInstanceOf(AllcllException.class)
+            .hasMessageContaining(expectExceptionMessage);
+    }
+}