feat : 코딩 테스트 코드 자동 저장(Draft) 기능 및 동시성 제어 구현

src/main/java/org/ezcode/codetest/application/draft/dto/request/DraftSaveRequest.java

@@ -0,0 +1,19 @@
+package org.ezcode.codetest.application.draft.dto.request;
+
+import jakarta.validation.constraints.NotNull;
+import jakarta.validation.constraints.Size;
+
+public record DraftSaveRequest(
+	@NotNull(message = "문제 ID는 필수입니다.")
+	Long problemId,
+
+	@NotNull(message = "언어 ID는 필수입니다.")
+	Long languageId,
+
+	@NotNull(message = "코드는 필수입니다.")
+	@Size(max = 100000, message = "코드는 최대 100,000자까지 입력 가능합니다.")
+	String code,
+
+	Long version  // 새 엔티티는 null일 수 있으므로 @NotNull 제외
+) {
+}

src/main/java/org/ezcode/codetest/application/draft/dto/response/DraftResponse.java

@@ -0,0 +1,22 @@
+package org.ezcode.codetest.application.draft.dto.response;
+
+import org.ezcode.codetest.domain.draft.model.entity.Draft;
+
+import lombok.Builder;
+
+@Builder
+public record DraftResponse(
+	Long problemId,
+	Long languageId,
+	String code,
+	Long version
+) {
+	public static DraftResponse from(Draft draft) {
+		return DraftResponse.builder()
+			.problemId(draft.getProblem().getId())
+			.languageId(draft.getLanguage().getId())
+			.code(draft.getCode())
+			.version(draft.getVersion())
+			.build();
+	}
+}

src/main/java/org/ezcode/codetest/application/draft/servcie/DraftService.java

@@ -0,0 +1,68 @@
+package org.ezcode.codetest.application.draft.servcie;
+
+import java.util.Optional;
+
+import org.ezcode.codetest.application.draft.dto.request.DraftSaveRequest;
+import org.ezcode.codetest.application.draft.dto.response.DraftResponse;
+import org.ezcode.codetest.domain.draft.exception.DraftException;
+import org.ezcode.codetest.domain.draft.exception.DraftExceptionCode;
+import org.ezcode.codetest.domain.draft.model.entity.Draft;
+import org.ezcode.codetest.domain.draft.service.DraftDomainService;
+import org.ezcode.codetest.domain.language.model.entity.Language;
+import org.ezcode.codetest.domain.language.service.LanguageDomainService;
+import org.ezcode.codetest.domain.problem.model.entity.Problem;
+import org.ezcode.codetest.domain.problem.service.ProblemDomainService;
+import org.ezcode.codetest.domain.user.model.entity.User;
+import org.ezcode.codetest.domain.user.service.UserDomainService;
+import org.springframework.orm.ObjectOptimisticLockingFailureException;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+
+@Slf4j
+@Service
+@RequiredArgsConstructor
+public class DraftService {
+
+	private final DraftDomainService draftDomainService;
+
+	private final UserDomainService userDomainService;
+	private final ProblemDomainService problemDomainService;
+	private final LanguageDomainService languageDomainService;
+
+	@Transactional
+	public DraftResponse autoSave(Long userId, DraftSaveRequest request) {
+
+		User user = userDomainService.getUserById(userId);
+		Problem problem = problemDomainService.getProblem(request.problemId());
+		Language language = languageDomainService.getLanguage(request.languageId());
+
+		Draft draft;
+		try {
+			draft = draftDomainService.autoSave(
+				user,
+				problem,
+				language,
+				request.code(),
+				request.version()
+			);
+		} catch (ObjectOptimisticLockingFailureException e) {
+			throw new DraftException(DraftExceptionCode.DRAFT_VERSION_CONFLICT);
+		}
+
+		return DraftResponse.from(draft);
+	}
+
+	@Transactional(readOnly = true)
+	public Optional<DraftResponse> getDraft(Long userId, Long problemId, Long languageId) {
+
+		User user = userDomainService.getUserById(userId);
+		Problem problem = problemDomainService.getProblem(problemId);
+		Language language = languageDomainService.getLanguage(languageId);
+
+		return draftDomainService.getDraft(user, problem, language)
+			.map(DraftResponse::from);
+	}
+}

src/main/java/org/ezcode/codetest/domain/draft/exception/DraftException.java

@@ -0,0 +1,21 @@
+package org.ezcode.codetest.domain.draft.exception;
+
+import org.ezcode.codetest.common.base.exception.BaseException;
+import org.ezcode.codetest.common.base.exception.ResponseCode;
+import org.springframework.http.HttpStatus;
+
+import lombok.Getter;
+
+@Getter
+public class DraftException extends BaseException {
+
+    private final ResponseCode responseCode;
+    private final HttpStatus httpStatus;
+    private final String message;
+
+    public DraftException(ResponseCode responseCode) {
+        this.responseCode = responseCode;
+        this.httpStatus = responseCode.getStatus();
+        this.message = responseCode.getMessage();
+    }
+}

src/main/java/org/ezcode/codetest/domain/draft/exception/DraftExceptionCode.java

@@ -0,0 +1,25 @@
+package org.ezcode.codetest.domain.draft.exception;
+
+import org.ezcode.codetest.common.base.exception.ResponseCode;
+import org.springframework.http.HttpStatus;
+
+import lombok.Getter;
+import lombok.RequiredArgsConstructor;
+
+@Getter
+@RequiredArgsConstructor
+public enum DraftExceptionCode implements ResponseCode {
+
+	DRAFT_NOT_FOUND(false, HttpStatus.NOT_FOUND, "해당 임시 저장 내역이 존재하지 않습니다."),
+
+	// 409 Conflict: 낙관적 락 충돌 발생 시 사용
+	DRAFT_VERSION_CONFLICT(false, HttpStatus.CONFLICT, "다른 탭에서 저장된 최신 코드가 존재합니다. 새로고침이 필요합니다."),
+
+	// 본인의 Draft가 아닌데 조회/수정하려 할 때 (URL 조작 등)
+	DRAFT_ACCESS_DENIED(false, HttpStatus.FORBIDDEN, "해당 임시 저장 내역에 접근할 권한이 없습니다."),
+	;
+
+	private final boolean success;
+	private final HttpStatus status;
+	private final String message;
+}

src/main/java/org/ezcode/codetest/domain/draft/model/entity/Draft.java

@@ -0,0 +1,72 @@
+package org.ezcode.codetest.domain.draft.model.entity;
+
+import org.ezcode.codetest.domain.language.model.entity.Language;
+import org.ezcode.codetest.domain.problem.model.entity.Problem;
+import org.ezcode.codetest.domain.user.model.entity.User;
+
+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.Lob;
+import jakarta.persistence.ManyToOne;
+import jakarta.persistence.Table;
+import jakarta.persistence.UniqueConstraint;
+import jakarta.persistence.Version;
+import lombok.AccessLevel;
+import lombok.Builder;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+
+@Entity
+@Table(
+	name = "draft",
+	uniqueConstraints = {
+		// 언어별 저장 지원
+		@UniqueConstraint(
+			name = "uk_draft_user_problem_language",
+			columnNames = {"user_id", "problem_id", "language_id"}
+		)
+	}
+)
+@Getter
+@NoArgsConstructor(access = AccessLevel.PROTECTED)
+public class Draft {
+
+	@Id
+	@GeneratedValue(strategy = GenerationType.IDENTITY)
+	private Long id;
+
+	@ManyToOne(fetch = FetchType.LAZY)
+	@JoinColumn(name = "user_id", nullable = false)
+	private User user;
+
+	@ManyToOne(fetch = FetchType.LAZY)
+	@JoinColumn(name = "problem_id", nullable = false)
+	private Problem problem;
+
+	@ManyToOne(fetch = FetchType.LAZY)
+	@JoinColumn(name = "language_id", nullable = false)
+	private Language language;
+
+	@Lob
+	private String code;
+
+	@Version        // 낙관적 락을 위한 버전 관리
+	private Long version;
+
+	public void updateCode(String newCode) {
+		this.code = newCode;
+	}
+
+	@Builder
+	public Draft(User user, Problem problem, Language language, String code, Long version) {
+		this.user = user;
+		this.problem = problem;
+		this.language = language;
+		this.code = code;
+		this.version = version;
+	}
+}

src/main/java/org/ezcode/codetest/domain/draft/repository/DraftRepository.java

@@ -0,0 +1,18 @@
+package org.ezcode.codetest.domain.draft.repository;
+
+import java.util.Optional;
+
+import org.ezcode.codetest.domain.draft.model.entity.Draft;
+import org.ezcode.codetest.domain.language.model.entity.Language;
+import org.ezcode.codetest.domain.problem.model.entity.Problem;
+import org.ezcode.codetest.domain.user.model.entity.User;
+
+public interface DraftRepository {
+
+	Draft save(Draft draft);
+
+	Optional<Draft> findByUserAndProblemAndLanguage(User user, Problem problem, Language language);
+
+	Draft saveAndFlush(Draft draft);
+
+}

src/main/java/org/ezcode/codetest/domain/draft/service/DraftDomainService.java

@@ -0,0 +1,57 @@
+package org.ezcode.codetest.domain.draft.service;
+
+import java.util.Optional;
+
+import org.ezcode.codetest.domain.draft.exception.DraftException;
+import org.ezcode.codetest.domain.draft.exception.DraftExceptionCode;
+import org.ezcode.codetest.domain.draft.model.entity.Draft;
+import org.ezcode.codetest.domain.draft.repository.DraftRepository;
+import org.ezcode.codetest.domain.language.model.entity.Language;
+import org.ezcode.codetest.domain.problem.model.entity.Problem;
+import org.ezcode.codetest.domain.user.model.entity.User;
+import org.springframework.stereotype.Service;
+
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+
+@Slf4j
+@Service
+@RequiredArgsConstructor
+public class DraftDomainService {
+
+	private final DraftRepository draftRepository;
+
+	public Draft autoSave(User user, Problem problem, Language language, String code, Long version) {
+
+		Optional<Draft> existingDraftOpt = draftRepository.findByUserAndProblemAndLanguage(user, problem, language);
+
+		if (existingDraftOpt.isPresent()) {
+			Draft draft = existingDraftOpt.get();
+
+			// 명시적 버전 검증: 클라이언트가 보낸 version과 DB의 version이 일치해야 함
+			if (version != null && !draft.getVersion().equals(version)) {
+				throw new DraftException(DraftExceptionCode.DRAFT_VERSION_CONFLICT);
+			}
+
+			draft.updateCode(code);
+			draftRepository.saveAndFlush(draft);
+
+			return draft;
+		} else {
+			// 새 엔티티인 경우
+			Draft draft = Draft.builder()
+				.user(user)
+				.problem(problem)
+				.language(language)
+				.code(code)
+				.build();
+
+			return draftRepository.saveAndFlush(draft);
+		}
+	}
+
+	public Optional<Draft> getDraft(User user, Problem problem, Language language) {
+
+		return draftRepository.findByUserAndProblemAndLanguage(user, problem, language);
+	}
+}

src/main/java/org/ezcode/codetest/infrastructure/persistence/repository/draft/DraftJpaRepository.java

@@ -0,0 +1,14 @@
+package org.ezcode.codetest.infrastructure.persistence.repository.draft;
+
+import java.util.Optional;
+
+import org.ezcode.codetest.domain.draft.model.entity.Draft;
+import org.ezcode.codetest.domain.language.model.entity.Language;
+import org.ezcode.codetest.domain.problem.model.entity.Problem;
+import org.ezcode.codetest.domain.user.model.entity.User;
+import org.springframework.data.jpa.repository.JpaRepository;
+
+public interface DraftJpaRepository extends JpaRepository<Draft, Long> {
+
+	Optional<Draft> findByUserAndProblemAndLanguage(User user, Problem problem, Language language);
+}

src/main/java/org/ezcode/codetest/infrastructure/persistence/repository/draft/DraftRepositoryImpl.java

@@ -0,0 +1,37 @@
+package org.ezcode.codetest.infrastructure.persistence.repository.draft;
+
+import java.util.Optional;
+
+import org.ezcode.codetest.domain.draft.model.entity.Draft;
+import org.ezcode.codetest.domain.draft.repository.DraftRepository;
+import org.ezcode.codetest.domain.language.model.entity.Language;
+import org.ezcode.codetest.domain.problem.model.entity.Problem;
+import org.ezcode.codetest.domain.user.model.entity.User;
+import org.springframework.stereotype.Repository;
+
+import lombok.RequiredArgsConstructor;
+
+@Repository
+@RequiredArgsConstructor
+public class DraftRepositoryImpl implements DraftRepository {
+
+	private final DraftJpaRepository draftJpaRepository;
+
+	@Override
+	public Draft save(Draft draft) {
+
+		return draftJpaRepository.save(draft);
+	}
+
+	@Override
+	public Optional<Draft> findByUserAndProblemAndLanguage(User user, Problem problem, Language language) {
+
+		return draftJpaRepository.findByUserAndProblemAndLanguage(user, problem, language);
+	}
+
+	@Override
+	public Draft saveAndFlush(Draft draft) {
+
+		return draftJpaRepository.saveAndFlush(draft);
+	}
+}