Feat: 쿠폰 관련 서비스 메서드 추가

Author: ense333

src/main/java/com/threestar/trainus/domain/coupon/user/repository/UserCouponRepository.java

@@ -1,6 +1,7 @@
 package com.threestar.trainus.domain.coupon.user.repository;
 
 import java.util.List;
+import java.util.Optional;
 
 import org.springframework.data.jpa.repository.JpaRepository;
 import org.springframework.data.jpa.repository.Query;
@@ -12,6 +13,8 @@
 public interface UserCouponRepository extends JpaRepository<UserCoupon, Long> {
 	boolean existsByUserIdAndCouponId(Long userId, Long couponId);
 
+	Optional<UserCoupon> findByUserIdAndCouponId(Long userId, Long couponId);
+
 	@Query("SELECT uc FROM UserCoupon uc JOIN FETCH uc.coupon WHERE uc.user.id = :userId")
 	List<UserCoupon> findAllByUserIdWithCoupon(@Param("userId") Long userId);
 

src/main/java/com/threestar/trainus/domain/coupon/user/service/CouponService.java

@@ -94,4 +94,35 @@ public CouponPageResponseDto getCoupons(Long userId) {
 			.coupons(dtoList)
 			.build();
 	}
+
+	@Transactional
+	public UserCoupon getValidUserCoupon(Long userCouponId, Long userId) {
+		return userCouponRepository.findByUserIdAndCouponId(userId, userCouponId)
+			.filter(c -> c.getStatus() == CouponStatus.ACTIVE)
+			.orElseThrow(() -> new BusinessException(ErrorCode.COUPON_NOT_FOUND));
+	}
+
+	public int calculateDiscountedPrice(int originalPrice, UserCoupon coupon) {
+		String discountPrice = coupon.getCoupon().getDiscountPrice();
+		if (discountPrice.contains("%")) {
+			int discountPercentage = Integer.parseInt(discountPrice.substring(0, discountPrice.indexOf("%")));
+			return originalPrice * discountPercentage / 100;
+		} else {
+			return Integer.parseInt(discountPrice.replace("원", ""));
+		}
+	}
+
+	public void useCoupon(UserCoupon coupon) {
+		if (coupon.getStatus() == CouponStatus.ACTIVE) {
+			coupon.use();
+			userCouponRepository.save(coupon);
+		}
+	}
+
+	public void restoreCoupon(UserCoupon coupon) {
+		if (coupon.getStatus() == CouponStatus.INACTIVE) {
+			coupon.restore();
+			userCouponRepository.save(coupon);
+		}
+	}
 }