refactor: 상품 상세 조회 최적화

- brandId 캐시 사용으로 불필요한 DB 조회 제거
- 실시간 랭킹 조회 연동

Author: sylee6529

apps/commerce-api/src/main/java/com/loopers/application/product/ProductFacade.java

@@ -2,13 +2,12 @@
 
 import com.loopers.application.event.product.ProductViewedEvent;
 import com.loopers.domain.like.service.LikeReadService;
-import com.loopers.domain.product.Product;
-import com.loopers.domain.product.repository.ProductRepository;
 import com.loopers.domain.product.service.ProductReadService;
 import com.loopers.domain.product.command.ProductSearchFilter;
 import com.loopers.domain.product.enums.ProductSortCondition;
 import com.loopers.infrastructure.cache.ProductDetailCache;
 import com.loopers.infrastructure.cache.ProductListCache;
+import com.loopers.infrastructure.cache.ProductRankingCache;
 import lombok.RequiredArgsConstructor;
 import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.data.domain.Page;
@@ -29,7 +28,7 @@ public class ProductFacade {
     private final LikeReadService likeReadService;
     private final ProductDetailCache productDetailCache;
     private final ProductListCache productListCache;
-    private final ProductRepository productRepository;
+    private final ProductRankingCache productRankingCache;
     private final ApplicationEventPublisher eventPublisher;
 
     @Transactional(readOnly = true)
@@ -100,33 +99,33 @@ public ProductDetailInfo getProductDetail(Long productId, Long memberIdOrNull) {
                     return result;
                 });
 
-        // 2. Product 엔티티 조회 (brandId 획득용)
-        Product product = productRepository.findById(productId)
-                .orElseThrow(() -> new com.loopers.support.error.CoreException(
-                        com.loopers.support.error.ErrorType.NOT_FOUND,
-                        "상품을 찾을 수 없습니다."));
-
-        // 3. isLikedByMember 동적 계산
+        // 2. isLikedByMember 동적 계산
         boolean isLiked = memberIdOrNull != null && likeReadService.isLikedBy(memberIdOrNull, productId);
 
-        // 4. isLikedByMember 필드만 교체해서 반환
+        // 3. 순위 조회 (실시간)
+        Integer ranking = productRankingCache.getRank(productId);
+
+        // 4. 동적 필드(isLikedByMember, ranking)를 교체해서 반환
         ProductDetailInfo result = ProductDetailInfo.builder()
                 .id(cachedInfo.getId())
                 .name(cachedInfo.getName())
                 .description(cachedInfo.getDescription())
+                .brandId(cachedInfo.getBrandId())
                 .brandName(cachedInfo.getBrandName())
                 .brandDescription(cachedInfo.getBrandDescription())
                 .price(cachedInfo.getPrice())
                 .stock(cachedInfo.getStock())
                 .likeCount(cachedInfo.getLikeCount())
-                .isLikedByMember(isLiked)  // ⭐ 동적 계산
+                .isLikedByMember(isLiked)
+                .ranking(ranking)
                 .build();
 
         // 5. ProductViewedEvent 발행 (조회수 집계)
+        // brandId는 캐시된 정보에서 가져옴 (불필요한 DB 조회 제거)
         eventPublisher.publishEvent(new ProductViewedEvent(
             memberIdOrNull,  // 비로그인 사용자는 null
             productId,
-            product.getBrandId(),
+            cachedInfo.getBrandId(),
             LocalDateTime.now()
         ));