✨ Feat: 색상 편지지 구매 로직

src/main/java/com/example/egobook_be/domain/letters/dto/request/CreateLetterRequest.java

@@ -23,7 +23,8 @@ public class CreateLetterRequest {
     @Schema(description = "편지 내용(360자 이하)", example = "요즘 자꾸 불안해져서... 누가 한마디 해주면 좋겠어.")
     private String text;
 
+
     @Schema(description = "배경 기본은 하얀색", example = "WHITE", nullable = true)
-    @NotNull
     private PlazaLetterColor backgroundColor;
+
 }

src/main/java/com/example/egobook_be/domain/letters/dto/response/CreateLetterResponse.java

@@ -14,5 +14,6 @@ public record CreateLetterResponse(
         PlazaLetterMode mode,
         String fromLabel,
         String backgroundColor,
-        OffsetDateTime createdAt
-) {}
+        OffsetDateTime createdAt,
+        String backgroundImageUrl
+        ) {}

src/main/java/com/example/egobook_be/domain/letters/enums/LettersErrorCode.java

@@ -20,6 +20,9 @@ public enum LettersErrorCode implements BaseErrorCode {
     INVALID_REPORT_REASON(HttpStatus.BAD_REQUEST, "PLAZA400_INVALID_REPORT_REASON", "잘못된 신고 사유입니다."),
     ALREADY_REPORTED(HttpStatus.BAD_REQUEST, "PLAZA400_ALREADY_REPORTED", "이미 신고한 답장입니다."),
     NOT_FRIEND(HttpStatus.BAD_REQUEST, "PLAZA400_NOT_FRIEND", "친구 관계가 아닙니다."),
+    INSUFFICIENT_INK(HttpStatus.BAD_REQUEST, "PLAZA400_INSUFFICIENT_INK", "잉크가 부족합니다."),
+
+
 
 
 
@@ -34,6 +37,7 @@ public enum LettersErrorCode implements BaseErrorCode {
     USER_NOT_FOUND(HttpStatus.NOT_FOUND,"PLAZA404_USER_NOT_FOUND", "유저를 찾을 수 없어요."),
 
 
+
     // 409
     ALREADY_REPLIED(HttpStatus.CONFLICT, "PLAZA409_ALREADY_REPLIED", "이미 답장한 편지예요"),
     ALREADY_GAVE_UP(HttpStatus.CONFLICT, "PLAZA409_ALREADY_GAVE_UP", "24시간이 지나 답장할 수 없어요"),

src/main/java/com/example/egobook_be/domain/letters/enums/PlazaLetterColor.java

@@ -16,5 +16,6 @@ public enum PlazaLetterColor {
     public int getPrice() {
         return price;
     }
+
 }
 

src/main/java/com/example/egobook_be/domain/letters/service/PlazaLetterService.java

@@ -36,6 +36,7 @@
 import org.springframework.transaction.annotation.Transactional;
 import lombok.RequiredArgsConstructor;
 import org.springframework.stereotype.Service;
+import org.springframework.beans.factory.annotation.Value;
 
 
 import java.time.*;
@@ -66,6 +67,10 @@ public class PlazaLetterService {
 
     private final NotificationService notificationService;
 
+    @Value("${spring.cloud.aws.cloudfront.domain}")
+    private String cloudfrontDomain;
+
+
     @Transactional(readOnly = true)
     public InboxNextResponse getNextArrivedLetter(Long userId) {
         return plazaLetterRepository
@@ -118,8 +123,35 @@ public CreateLetterResponse createLetter(Long userId, CreateLetterRequest reques
             }
         }
 
+        // =========================
+        // 편지지 색상/잉크 결제 로직
+        // - null 또는 WHITE => WHITE로 확정, price=0, 차감 없음
+        // - 유료 색상 => 잉크 부족 체크 + 차감 + 로그
+        // =========================
+        // 1. 색상 안전 처리
+        PlazaLetterColor color =
+                (request.getBackgroundColor() == null)
+                        ? PlazaLetterColor.WHITE
+                        : request.getBackgroundColor();
+
+// 2. 가격 조회
+        int price = color.getPrice(); // WHITE면 0
+
+// 3. 잉크 차감 (유료일 때만)
+        if (price > 0) {
+            user.usingInk(price);   // 부족하면 여기서 예외 발생
+
+            InkLog inkLog = InkLog.builder()
+                    .user(user)
+                    .amount(-price)
+                    .reason(InkLogType.LETTER_COLOR_PURCHASE)
+                    .build();
+
+            inkLogRepository.save(inkLog);
+        }
+
+
         PlazaLetterThread thread = plazaLetterThreadRepository.save(PlazaLetterThread.createNow());
-        String bg = request.getBackgroundColor() == null ? "WHITE" : request.getBackgroundColor().name();
 
         String fromLabel = "익명";
         if (request.getMode() == PlazaLetterMode.FRIEND) {
@@ -162,11 +194,11 @@ public CreateLetterResponse createLetter(Long userId, CreateLetterRequest reques
                 .mode(request.getMode())
                 .fromLabel(fromLabel)
                 .content(request.getText())
-                .backgroundColor(PlazaLetterColor.valueOf(bg))
-                .status(status)                    // ARRIVED or WAITING
+                .backgroundColor(color)
+                .status(status)
                 .createdAt(now)
-                .arrivedAt(arrivedAt)              // WAITING이면 null
-                .replyDeadlineAt(replyDeadlineAt)  // WAITING이면 null
+                .arrivedAt(arrivedAt)
+                .replyDeadlineAt(replyDeadlineAt)
                 .build();
 
         // =================================================
@@ -216,13 +248,22 @@ public CreateLetterResponse createLetter(Long userId, CreateLetterRequest reques
                     letter.getSenderId(), saved.getLetterId(), e);
         }
 
+
+        String imageUrl = null;
+        if (saved.getBackgroundColor() != PlazaLetterColor.WHITE) {
+            String fileName = saved.getBackgroundColor().name().substring(0, 1)
+                    + saved.getBackgroundColor().name().substring(1).toLowerCase();
+            imageUrl = cloudfrontDomain + "/letter/" + fileName + ".png";
+        }
+
         return CreateLetterResponse.builder()
                 .letterId(saved.getLetterId())
                 .threadId(saved.getThreadId())
                 .status(saved.getStatus())
                 .mode(saved.getMode())
                 .fromLabel(saved.getFromLabel())
                 .backgroundColor(saved.getBackgroundColor().name())
+                .backgroundImageUrl(imageUrl)
                 .createdAt(saved.getCreatedAt())
                 .build();
     }
@@ -269,19 +310,30 @@ private PlazaLetterColor resolveBackgroundColor(String requested) {
     }
 
 
+
     private void validateCreateLetterRequest(CreateLetterRequest request) {
-        if (request == null || request.getMode() == null) {
+        if (request == null) {
+            throw new CustomException(LettersErrorCode.INVALID_MODE);
+        }
+
+        if (request.getMode() == null) {
             throw new CustomException(LettersErrorCode.INVALID_MODE);
         }
+
         String text = request.getText();
         if (text == null || text.isBlank() || text.length() > LETTER_TEXT_LIMIT) {
             throw new CustomException(LettersErrorCode.LETTER_TEXT_LIMIT);
         }
+
         if (request.getMode() == PlazaLetterMode.FRIEND && request.getToFriendId() == null) {
             throw new CustomException(LettersErrorCode.FRIEND_ID_REQUIRED);
         }
+
+        // backgroundColor는 null 허용.
+        // null/WHITE면 이후 createLetter에서 WHITE로 보정 + price=0 처리함.
     }
 
+
     @Transactional
     public DeleteThreadResponse deleteThread(Long userId, Long threadId) {
         // 스레드 존재 체크

src/main/java/com/example/egobook_be/domain/user/entity/InkLogType.java

@@ -11,5 +11,6 @@ public enum InkLogType {
     DAILY_MISSION_REWARD,
     WEEKLY_MISSION_REWARD,
     WATCH_AD,
-    WEEKLY_UNLOCK
+    WEEKLY_UNLOCK,
+    LETTER_COLOR_PURCHASE
 }

src/main/java/com/example/egobook_be/domain/user/entity/User.java

@@ -1,10 +1,12 @@
 package com.example.egobook_be.domain.user.entity;
 
 import com.example.egobook_be.domain.ego_room.enums.CounselTone;
+import com.example.egobook_be.domain.letters.enums.LettersErrorCode;
 import com.example.egobook_be.domain.shop.entity.UserItem;
 import com.example.egobook_be.domain.user.enums.RoleType;
 import com.example.egobook_be.domain.user.enums.UserStatus;
 import com.example.egobook_be.global.entity.BaseTimeEntity;
+import com.example.egobook_be.global.exception.CustomException;
 import jakarta.persistence.*;
 import lombok.*;
 
@@ -173,6 +175,16 @@ public void useInk(int price){
         this.ink -= price;
     }
 
+    public void usingInk(int price){
+        if (price <= 0) return;
+
+        if (this.ink == null || this.ink < price) {
+            throw new CustomException(LettersErrorCode.INSUFFICIENT_INK);
+        }
+
+        this.ink -= price;
+    }
+
     public void updateNotificationEnabled() {
         this.notificationEnabled = !this.notificationEnabled;
     }