#26 송금 요청 수락/거절 기능

src/main/java/com/donggi/sendzy/account/application/AccountLockingService.java

@@ -0,0 +1,54 @@
+package com.donggi.sendzy.account.application;
+
+import com.donggi.sendzy.account.domain.Account;
+import com.donggi.sendzy.account.domain.AccountRepository;
+import com.donggi.sendzy.account.domain.LockedAccounts;
+import com.donggi.sendzy.account.exception.AccountNotFoundException;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.util.List;
+import java.util.stream.Stream;
+
+@RequiredArgsConstructor
+@Service
+public class AccountLockingService {
+
+    private final AccountRepository accountRepository;
+
+    /**
+     * 두 개의 계좌를 계좌 ID 기준으로 오름차순 정렬하여 락을 획득합니다.
+     * 데드락을 방지하기 위해 항상 일정한 순서로 락을 획득합니다.
+     * @param senderId 송금 회원 ID
+     * @param receiverId 수신 회원 ID
+     * @return 락을 획득한 계좌 목록
+     */
+    @Transactional
+    public LockedAccounts getAccountsWithLockOrdered(final long senderId, final long receiverId) {
+        final List<Long> sortedIds = getSortedIds(senderId, receiverId);
+        final List<Account> lockedAccounts = sortedIds.stream()
+            .map(accountId -> accountRepository.findByMemberIdForUpdate(accountId)
+                .orElseThrow(() -> new AccountNotFoundException(accountId)))
+            .toList();
+
+        return LockedAccounts.of(lockedAccounts, senderId, receiverId);
+    }
+
+    /**
+     * 회원 ID로 계좌를 조회하고 해당 계좌의 락을 획득합니다.
+     * @param senderId 송신자 ID
+     * @return 조회된 계좌
+     */
+    @Transactional
+    public Account getByMemberIdForUpdate(final long senderId) {
+        return accountRepository.findByMemberIdForUpdate(senderId)
+            .orElseThrow(() -> new AccountNotFoundException(senderId));
+    }
+
+    private List<Long> getSortedIds(final long senderId, final long receiverId) {
+        return Stream.of(senderId, receiverId)
+            .sorted()
+            .toList();
+    }
+}

src/main/java/com/donggi/sendzy/account/domain/Account.java

@@ -22,11 +22,20 @@ public Account(final Long memberId) {
         this.pendingAmount = 0L;
     }
 
-    public void withdraw(final Long amount) {
+    public void reserveWithdraw(final Long amount) {
         validateWithdraw(amount);
         this.pendingAmount += amount;
     }
 
+    public void commitWithdraw(final long amount) {
+        this.balance -= amount;
+        this.pendingAmount -= amount;
+    }
+
+    public void cancelWithdraw(final long amount) {
+        this.pendingAmount -= amount;
+    }
+
     public void deposit(final Long amount) {
         final var fieldName = "amount";
         Validator.notNull(amount, fieldName);

src/main/java/com/donggi/sendzy/account/domain/AccountRepository.java

@@ -16,26 +16,18 @@ public interface AccountRepository {
      * @param memberId 회원 ID
      * @return 조회된 계좌
      */
-    Optional<Account> findByMemberId(final Long memberId);
+    Optional<Account> findByMemberId(final long memberId);
 
     /**
      * 회원 ID로 계좌를 조회하고, 조회된 계좌에 배타적 잠금(Exclusive Lock)을 겁니다.
      * @param memberId 회원 ID
      * @return 잠금이 설정된 계좌(Optional)
      */
-    Optional<Account> findByIdForUpdate(final Long memberId);
+    Optional<Account> findByMemberIdForUpdate(final long memberId);
 
     /**
-     * 계좌의 대기 중인 금액을 업데이트합니다.
-     * @param id 계좌 ID
-     * @param pendingAmount 대기 중인 금액
+     * 계좌를 업데이트합니다.
+     * @param account 업데이트할 계좌
      */
-    void updatePendingAmount(final Long id, final Long pendingAmount);
-
-    /**
-     * 계좌의 잔액을 업데이트합니다.
-     * @param id 계좌 ID
-     * @param balance 잔액
-     */
-    void updateBalance(final Long id, final Long balance);
+    void update(final Account account);
 }

src/main/java/com/donggi/sendzy/account/domain/AccountService.java

@@ -19,19 +19,26 @@ public Account getByMemberId(final long memberId) {
 
     @Transactional
     public void withdraw(final Account account, final long amount) {
-        account.withdraw(amount);
-        accountRepository.updatePendingAmount(account.getId(), account.getPendingAmount());
+        account.reserveWithdraw(amount);
+        accountRepository.update(account);
     }
 
     @Transactional
     public void deposit(final Account account, final long amount) {
         account.deposit(amount);
-        accountRepository.updateBalance(account.getId(), account.getBalance());
+        accountRepository.update(account);
     }
 
-    @Transactional(readOnly = true)
-    public Account getByIdForUpdate(final long memberId) {
-        return accountRepository.findByIdForUpdate(memberId)
-            .orElseThrow(() -> new AccountNotFoundException(memberId));
+    @Transactional
+    public void transfer(final Account sender, final Account receiver, final long amount) {
+        sender.commitWithdraw(amount);
+        receiver.deposit(amount);
+        accountRepository.update(sender);
+        accountRepository.update(receiver);
+    }
+
+    @Transactional
+    public void update(final Account account) {
+        accountRepository.update(account);
     }
 }

src/main/java/com/donggi/sendzy/account/domain/LockedAccounts.java

@@ -0,0 +1,23 @@
+package com.donggi.sendzy.account.domain;
+
+import java.util.List;
+
+/**
+ * 락이 걸린 송금자 계좌와 수신자 계좌를 묶어 표현하는 도메인 객체
+ *
+ * @param senderAccount 송금자 계좌
+ * @param receiverAccount 수신자 계좌
+ */
+public record LockedAccounts(
+    Account senderAccount,
+    Account receiverAccount
+) {
+    public static LockedAccounts of(final List<Account> lockedAccounts, final long senderId, final long receiverId) {
+        final var first = lockedAccounts.get(0);
+        final var second = lockedAccounts.get(1);
+
+        final var sender = first.getMemberId() == senderId ? first : second;
+        final var receiver = first.getMemberId() == receiverId ? first : second;
+        return new LockedAccounts(sender, receiver);
+    }
+}

src/main/java/com/donggi/sendzy/account/infrastructure/AccountMapper.java

@@ -4,19 +4,18 @@
 import com.donggi.sendzy.account.domain.AccountRepository;
 import com.donggi.sendzy.account.domain.TestAccountRepository;
 import org.apache.ibatis.annotations.Mapper;
-import org.apache.ibatis.annotations.Param;
 
 import java.util.Optional;
 
 @Mapper
 public interface AccountMapper extends AccountRepository, TestAccountRepository {
     Long create(final Account account);
 
-    Optional<Account> findByMemberId(final Long memberId);
-
     void deleteAll();
 
-    void updatePendingAmount(@Param("id") final Long id, @Param("pendingAmount") final Long pendingAmount);
+    void update(final Account account);
+
+    Optional<Account> findByMemberId(final long memberId);
 
-    void updateBalance(@Param("id") final Long id, @Param("balance") final Long balance);
+    Optional<Account> findByMemberIdForUpdate(final long memberId);
 }

src/main/java/com/donggi/sendzy/common/exception/ClientErrorControllerAdvice.java

@@ -3,7 +3,7 @@
 import com.donggi.sendzy.account.exception.InvalidWithdrawalException;
 import com.donggi.sendzy.member.exception.EmailDuplicatedException;
 import com.donggi.sendzy.member.exception.InvalidPasswordException;
-import com.donggi.sendzy.member.exception.MemberNotFoundException;
+import com.donggi.sendzy.remittance.exception.InvalidRemittanceRequestStatusException;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ProblemDetail;
 import org.springframework.security.access.AccessDeniedException;
@@ -85,4 +85,12 @@ public ProblemDetail handleInvalidWithdrawalException(final InvalidWithdrawalExc
     public ProblemDetail handleBadRequestException(final BadRequestException e) {
         return ProblemDetail.forStatusAndDetail(HttpStatus.BAD_REQUEST, e.getMessage());
     }
+
+    /**
+     * 송금 요청이 수락 또는 거절 가능한 상태가 아닌 경우
+     */
+    @ExceptionHandler(InvalidRemittanceRequestStatusException.class)
+    public ProblemDetail handleInvalidRemittanceRequestStatusException(final InvalidRemittanceRequestStatusException e) {
+        return ProblemDetail.forStatusAndDetail(HttpStatus.CONFLICT, e.getMessage());
+    }
 }

src/main/java/com/donggi/sendzy/remittance/application/RemittanceRequestApplicationService.java

@@ -1,7 +1,9 @@
 package com.donggi.sendzy.remittance.application;
 
+import com.donggi.sendzy.account.application.AccountLockingService;
 import com.donggi.sendzy.account.domain.Account;
 import com.donggi.sendzy.account.domain.AccountService;
+import com.donggi.sendzy.account.domain.LockedAccounts;
 import com.donggi.sendzy.common.exception.BadRequestException;
 import com.donggi.sendzy.member.domain.Member;
 import com.donggi.sendzy.member.domain.MemberService;
@@ -16,14 +18,12 @@
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
-import java.util.List;
-import java.util.stream.Stream;
-
 @Service
 @RequiredArgsConstructor
 public class RemittanceRequestApplicationService {
 
     private final AccountService accountService;
+    private final AccountLockingService accountLockingService;
     private final RemittanceHistoryService remittanceHistoryService;
     private final RemittanceRequestService remittanceRequestService;
     private final RemittanceStatusHistoryService remittanceStatusHistoryService;
@@ -40,12 +40,9 @@ public long createRemittanceRequest(final Long senderId, final Long receiverId,
         validateSenderAndReceiver(senderId, receiverId);
 
         // 계좌 ID를 오름차순으로 정렬하여 일관된 순서로 Lock 확보
-        List<Long> sortedIds = getSortedIds(senderId, receiverId);
-        final Account firstAccount = accountService.getByIdForUpdate(sortedIds.get(0));
-        final Account secondAccount = accountService.getByIdForUpdate(sortedIds.get(1));
-
-        final Account senderAccount = senderId.equals(firstAccount.getMemberId()) ? firstAccount : secondAccount;
-        final Account receiverAccount = receiverId.equals(firstAccount.getMemberId()) ? firstAccount : secondAccount;
+        final LockedAccounts lockedAccounts = accountLockingService.getAccountsWithLockOrdered(senderId, receiverId);
+        final Account senderAccount = lockedAccounts.senderAccount();
+        final Account receiverAccount = lockedAccounts.receiverAccount();
 
         final var sender = memberService.findById(senderAccount.getMemberId());
         final var receiver = memberService.findById(receiverAccount.getMemberId());
@@ -112,10 +109,4 @@ private void validateSenderAndReceiver(final Long senderId, final Long receiverI
             throw new BadRequestException("송금자와 수신자가 동일합니다.");
         }
     }
-
-    private List<Long> getSortedIds(final Long senderId, final Long receiverId) {
-        return Stream.of(senderId, receiverId)
-            .sorted()
-            .toList();
-    }
 }

src/main/java/com/donggi/sendzy/remittance/application/RemittanceRequestProcessor.java

@@ -0,0 +1,88 @@
+package com.donggi.sendzy.remittance.application;
+
+import com.donggi.sendzy.account.application.AccountLockingService;
+import com.donggi.sendzy.account.domain.AccountService;
+import com.donggi.sendzy.account.domain.LockedAccounts;
+import com.donggi.sendzy.remittance.domain.RemittanceRequest;
+import com.donggi.sendzy.remittance.domain.RemittanceRequestStatus;
+import com.donggi.sendzy.remittance.domain.RemittanceStatusHistory;
+import com.donggi.sendzy.remittance.domain.service.RemittanceRequestService;
+import com.donggi.sendzy.remittance.domain.service.RemittanceStatusHistoryService;
+import com.donggi.sendzy.remittance.exception.InvalidRemittanceRequestStatusException;
+import lombok.RequiredArgsConstructor;
+import org.springframework.security.access.AccessDeniedException;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@RequiredArgsConstructor
+@Service
+public class RemittanceRequestProcessor {
+
+    private final RemittanceRequestService remittanceRequestService;
+    private final AccountLockingService accountLockingService;
+    private final RemittanceStatusHistoryService remittanceStatusHistoryService;
+    private final AccountService accountService;
+
+    @Transactional
+    public void handleAcceptance(final long requestId, final long receiverId) {
+        // 송금 요청 조회 및 상태 확인 (PENDING 여부)
+        final var remittanceRequest = remittanceRequestService.getByIdForUpdate(requestId);
+        validateReceiverAuthorityAndStatus(remittanceRequest, receiverId);
+
+        // 송금자/수신자 계좌 락 + 조회 (ID 오름차순 → 데드락 방지)
+        final LockedAccounts lockedAccounts = accountLockingService.getAccountsWithLockOrdered(remittanceRequest.getSenderId(), remittanceRequest.getReceiverId());
+        final var senderAccount = lockedAccounts.senderAccount();
+        final var receiverAccount = lockedAccounts.receiverAccount();
+
+        // 이체 처리
+        accountService.transfer(senderAccount, receiverAccount, remittanceRequest.getAmount());
+
+        // 송금 요청 상태 변경 → ACCEPTED
+        remittanceRequestService.accept(remittanceRequest);
+
+        // 상태 변경 히스토리 저장
+        recordStatus(remittanceRequest, RemittanceRequestStatus.ACCEPTED);
+    }
+
+    @Transactional
+    public void handleRejection(final long requestId, final long receiverId) {
+        // 송금 요청 조회 (락 획득)
+        final var remittanceRequest = remittanceRequestService.getByIdForUpdate(requestId);
+
+        // 수신자 권한 확인
+        validateReceiverAuthorityAndStatus(remittanceRequest, receiverId);
+
+        // 송금자 계좌 롤백 처리
+        final var senderAccount = accountLockingService.getByMemberIdForUpdate(remittanceRequest.getSenderId());
+        senderAccount.cancelWithdraw(remittanceRequest.getAmount());
+        accountService.update(senderAccount);
+
+        // 송금 요청 상태 변경 → REJECTED
+        remittanceRequestService.reject(remittanceRequest);
+
+        // 상태 변경 히스토리 저장
+        recordStatus(remittanceRequest, RemittanceRequestStatus.REJECTED);
+    }
+
+    private void validateReceiverAuthorityAndStatus(final RemittanceRequest remittanceRequest, final long receiverId) {
+        if (!remittanceRequest.getReceiverId().equals(receiverId)) {
+            throw new AccessDeniedException("해당 송금 요청의 수신자만 처리할 수 있습니다.");
+        }
+
+        if (!remittanceRequest.isPending()) {
+            throw new InvalidRemittanceRequestStatusException(remittanceRequest.getStatus());
+        }
+    }
+
+    private void recordStatus(RemittanceRequest request, RemittanceRequestStatus status) {
+        remittanceStatusHistoryService.recordStatusHistory(
+            new RemittanceStatusHistory(
+                request.getId(),
+                request.getSenderId(),
+                request.getReceiverId(),
+                request.getAmount(),
+                status
+            )
+        );
+    }
+}

src/main/java/com/donggi/sendzy/remittance/controller/RemittanceRequestRestController.java

@@ -0,0 +1,40 @@
+package com.donggi.sendzy.remittance.controller;
+
+import com.donggi.sendzy.common.security.CustomUserDetails;
+import com.donggi.sendzy.remittance.application.RemittanceRequestProcessor;
+import lombok.RequiredArgsConstructor;
+import org.springframework.security.core.annotation.AuthenticationPrincipal;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+@RequiredArgsConstructor
+@RestController
+@RequestMapping("/v1/remittance")
+public class RemittanceRequestRestController {
+
+    private final RemittanceRequestProcessor remittanceRequestProcessor;
+
+    /**
+     * 송금 요청 수락
+     * @param requestId 송금 요청 ID
+     * @param userDetails 로그인 정보
+     */
+    @PostMapping("/{requestId}/accept")
+    public void accept(@PathVariable("requestId") final long requestId, @AuthenticationPrincipal final CustomUserDetails userDetails) {
+        final var receiverId = userDetails.getMemberId();
+        remittanceRequestProcessor.handleAcceptance(requestId, receiverId);
+    }
+
+    /**
+     * 송금 요청 거절
+     * @param requestId 송금 요청 ID
+     * @param userDetails 로그인 정보
+     */
+    @PostMapping("/{requestId}/reject")
+    public void reject(@PathVariable("requestId") final long requestId, @AuthenticationPrincipal final CustomUserDetails userDetails) {
+        final var receiverId = userDetails.getMemberId();
+        remittanceRequestProcessor.handleRejection(requestId, receiverId);
+    }
+}