[Feature] 아이템 구매 기능

server/src/main/java/com/soopgyeol/api/common/exception/InsufficientBalanceException.java

@@ -0,0 +1,7 @@
+package com.soopgyeol.api.common.exception;
+
+public class InsufficientBalanceException extends RuntimeException {
+    public InsufficientBalanceException(String message) {
+        super(message);
+    }
+}

server/src/main/java/com/soopgyeol/api/common/exception/ItemAlreadyOwnedException.java

@@ -0,0 +1,8 @@
+package com.soopgyeol.api.common.exception;
+
+public class ItemAlreadyOwnedException extends RuntimeException {
+    public ItemAlreadyOwnedException(String message) {
+        super(message);
+    }
+}
+

server/src/main/java/com/soopgyeol/api/controller/AuthController.java

@@ -83,7 +83,7 @@ public void kakaoAutoLogin(@RequestParam String code, HttpServletResponse respon
 
 
 
-//    // 임시 토큰 생성시 활성화
+    // 임시 토큰 생성시 활성화
 //    private final UserRepository userRepository;
 //    private final JwtProvider jwtProvider;
 //    @PostMapping("/dev-login")

server/src/main/java/com/soopgyeol/api/controller/BuyController.java

@@ -0,0 +1,38 @@
+package com.soopgyeol.api.controller;
+
+import com.soopgyeol.api.domain.buy.dto.*;
+import com.soopgyeol.api.service.jwt.JwtProvider;
+import com.soopgyeol.api.service.buy.BuyService;
+import lombok.RequiredArgsConstructor;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.*;
+
+import java.util.List;
+
+@RestController
+@RequestMapping("/items/buy")
+@RequiredArgsConstructor
+public class BuyController {
+
+    private final BuyService buyService;
+    private final JwtProvider jwtProvider;
+
+    @PostMapping
+    public ResponseEntity<BuyResponse> buyItem(@RequestHeader("Authorization") String authorizationHeader,
+                                          @RequestBody BuyRequest request) {
+        String token = authorizationHeader.replace("Bearer ", "");
+        Long userId = jwtProvider.getUserId(token);
+
+        BuyResult result = buyService.buyItem(userId, request.getItemId());
+
+        BuyResponse response = BuyResponse.builder()
+                .itemId(result.getItemId())
+                .itemName(result.getItemName())
+                .itemPrice(result.getItemPrice())
+                .userMoneyBalance(result.getUserMoneyBalance())
+                .message("구매가 완료되었습니다.")
+                .build();
+
+        return ResponseEntity.ok(response);
+    }
+}

server/src/main/java/com/soopgyeol/api/domain/buy/dto/BuyRequest.java

@@ -0,0 +1,8 @@
+package com.soopgyeol.api.domain.buy.dto;
+
+import lombok.Getter;
+
+@Getter
+public class BuyRequest {
+    private Long itemId;   // 구매하려는 아이템 ID
+}

server/src/main/java/com/soopgyeol/api/domain/buy/dto/BuyResponse.java

@@ -0,0 +1,16 @@
+package com.soopgyeol.api.domain.buy.dto;
+
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Getter;
+
+@Builder
+@Getter
+@AllArgsConstructor
+public class BuyResponse {
+    private Long itemId;
+    private String itemName;
+    private int itemPrice;
+    private int userMoneyBalance;
+    private String message;
+}

server/src/main/java/com/soopgyeol/api/domain/buy/dto/BuyResult.java

@@ -0,0 +1,13 @@
+package com.soopgyeol.api.domain.buy.dto;
+
+import lombok.Builder;
+import lombok.Getter;
+
+@Getter
+@Builder
+public class BuyResult {
+    private Long itemId;
+    private String itemName;
+    private int itemPrice;
+    private int userMoneyBalance;
+}

server/src/main/java/com/soopgyeol/api/domain/buy/entity/Purchase.java

@@ -0,0 +1,36 @@
+package com.soopgyeol.api.domain.buy.entity;
+
+import com.soopgyeol.api.domain.user.User;
+import jakarta.persistence.*;
+import lombok.*;
+import com.soopgyeol.api.domain.item.entity.Item;
+import org.hibernate.annotations.CreationTimestamp;
+import java.time.LocalDateTime;
+
+@Entity
+@Getter
+@NoArgsConstructor
+@AllArgsConstructor
+@Builder
+public class Purchase {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    @Column(name = "buy_id")
+    private Long id;
+
+    @ManyToOne(optional = false, fetch = FetchType.LAZY)
+    @JoinColumn(name = "user_id")
+    private User user;  // 구매자 (FK)
+
+    @ManyToOne(optional = false, fetch = FetchType.LAZY)
+    @JoinColumn(name = "item_id")
+    private Item item;  // 구매한 아이템 (FK)
+
+    @Column(name = "item_money", nullable = false)
+    private int itemMoney;
+
+    @CreationTimestamp
+    @Column(name = "purchased_at", nullable = false, updatable = false)
+    private LocalDateTime purchasedAt;  // 구매 시각
+}

server/src/main/java/com/soopgyeol/api/domain/item/entity/Item.java

@@ -27,4 +27,8 @@ public class Item {
   @Enumerated(EnumType.STRING)
   @Column(nullable = false)
   private ItemCategory category;
+
+  public void setPrice(int price) {
+    this.price = price;
+  }
 }

server/src/main/java/com/soopgyeol/api/domain/user/User.java

@@ -54,4 +54,6 @@ public void increaseGrowthPoint(int point) {
     public void addMoney(int amount) {
         this.moneyBalance += amount;
     }
+
+    public void subMoney(int money) {this.moneyBalance -= money; }
 }

server/src/main/java/com/soopgyeol/api/repository/PurchaseRepository.java

@@ -0,0 +1,13 @@
+package com.soopgyeol.api.repository;
+
+import com.soopgyeol.api.domain.item.entity.Item;
+import com.soopgyeol.api.domain.user.User;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Repository;
+import com.soopgyeol.api.domain.buy.entity.Purchase;
+
+@Repository
+public interface PurchaseRepository extends JpaRepository<Purchase, Long> {
+
+    boolean existsByUserAndItem(User user, Item item);
+}

server/src/main/java/com/soopgyeol/api/service/buy/BuyService.java

@@ -0,0 +1,7 @@
+package com.soopgyeol.api.service.buy;
+
+import com.soopgyeol.api.domain.buy.dto.BuyResult;
+
+public interface BuyService {
+    BuyResult buyItem(Long userId, Long itemId);   // 반드시 BuyResult로 변경
+}

server/src/main/java/com/soopgyeol/api/service/buy/BuyServiceImpl.java

@@ -0,0 +1,71 @@
+package com.soopgyeol.api.service.buy;
+
+import com.soopgyeol.api.domain.buy.dto.BuyResult;
+import com.soopgyeol.api.domain.buy.entity.Purchase;
+import com.soopgyeol.api.domain.item.entity.Item;
+import com.soopgyeol.api.domain.user.User;
+import com.soopgyeol.api.repository.ItemRepository;
+import com.soopgyeol.api.repository.PurchaseRepository;
+import com.soopgyeol.api.repository.UserRepository;
+import com.soopgyeol.api.common.exception.InsufficientBalanceException;
+import com.soopgyeol.api.common.exception.ItemAlreadyOwnedException;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@Service
+public class BuyServiceImpl implements BuyService {
+
+    private final ItemRepository itemRepository;
+    private final PurchaseRepository purchaseRepository;
+    private final UserRepository userRepository;
+
+    public BuyServiceImpl(ItemRepository itemRepository,
+                          PurchaseRepository purchaseRepository,
+                          UserRepository userRepository) {
+        this.itemRepository = itemRepository;
+        this.purchaseRepository = purchaseRepository;
+        this.userRepository = userRepository;
+    }
+
+    @Transactional
+    @Override
+    public BuyResult buyItem(Long userId, Long itemId) {
+
+        // 1. 구매 가능 여부 (사용자 금액과 아이템 금액 비교)
+        User user = userRepository.findById(userId)
+                .orElseThrow(() -> new RuntimeException("해당 유저가 존재하지 않습니다."));
+
+        Item item = itemRepository.findById(itemId)
+                .orElseThrow(() -> new IllegalArgumentException("아이템이 존재하지 않습니다."));
+
+        if (user.getMoneyBalance() < item.getPrice()) {
+            throw new InsufficientBalanceException("보유 금액이 부족합니다.");
+        }
+
+        // 2. 보유 중복 여부
+        boolean alreadyOwned = purchaseRepository.existsByUserAndItem(user, item);
+        if (alreadyOwned) {
+            throw new ItemAlreadyOwnedException("이미 보유한 아이템입니다.");
+        }
+
+        // 3. 금액 차감
+        int money = item.getPrice();
+        user.subMoney(money);
+
+        // 4. 인벤토리 저장
+        Purchase purchase = Purchase.builder()
+                .user(user)
+                .item(item)
+                .itemMoney(item.getPrice())
+                .build();
+
+        purchaseRepository.save(purchase);
+
+        return BuyResult.builder()
+                .itemId(item.getId())
+                .itemName(item.getName())
+                .itemPrice(item.getPrice())
+                .userMoneyBalance(user.getMoneyBalance())
+                .build();
+    }
+}