refactor: 테마 API 로깅 추가

src/main/kotlin/roomescape/theme/business/ThemeService.kt

@@ -1,5 +1,6 @@
 package roomescape.theme.business
 
+import io.github.oshai.kotlinlogging.KotlinLogging
 import org.springframework.data.repository.findByIdOrNull
 import org.springframework.stereotype.Service
 import org.springframework.transaction.annotation.Transactional
@@ -10,44 +11,71 @@ import roomescape.theme.infrastructure.persistence.ThemeRepository
 import roomescape.theme.web.*
 import java.time.LocalDate
 
+private val log = KotlinLogging.logger {}
+
 @Service
 class ThemeService(
-        private val themeRepository: ThemeRepository
+    private val themeRepository: ThemeRepository,
 ) {
     @Transactional(readOnly = true)
-    fun findById(id: Long): ThemeEntity = themeRepository.findByIdOrNull(id)
+    fun findById(id: Long): ThemeEntity {
-            ?: throw ThemeException(ThemeErrorCode.THEME_NOT_FOUND)
+        log.debug { "[ThemeService.findById] 테마 조회 시작: themeId=$id" }
+
+        return themeRepository.findByIdOrNull(id)
+            ?.also { log.info { "[ThemeService.findById] 테마 조회 완료: themeId=$id" } }
+            ?: run {
+                log.warn { "[ThemeService.findById] 테마 조회 실패: themeId=$id" }
+                throw ThemeException(ThemeErrorCode.THEME_NOT_FOUND)
+            }
+    }
 
     @Transactional(readOnly = true)
-    fun findThemes(): ThemeRetrieveListResponse = themeRepository.findAll()
+    fun findThemes(): ThemeRetrieveListResponse {
+        log.debug { "[ThemeService.findThemes] 모든 테마 조회 시작" }
+
+        return themeRepository.findAll()
+            .also { log.info { "[ThemeService.findThemes] ${it.size}개의 테마 조회 완료" } }
             .toResponse()
+    }
 
     @Transactional(readOnly = true)
     fun findMostReservedThemes(count: Int): ThemeRetrieveListResponse {
+        log.debug { "[ThemeService.findMostReservedThemes] 인기 테마 조회 시작: count=$count" }
+
         val today = LocalDate.now()
         val startDate = today.minusDays(7)
         val endDate = today.minusDays(1)
 
         return themeRepository.findPopularThemes(startDate, endDate, count)
-                .toResponse()
+            .also { log.info { "[ThemeService.findMostReservedThemes] ${it.size} 개의 인기 테마 조회 완료" } }
+            .toResponse()
     }
 
     @Transactional
     fun createTheme(request: ThemeCreateRequest): ThemeRetrieveResponse {
+        log.debug { "[ThemeService.createTheme] 테마 생성 시작: name=${request.name}" }
+
         if (themeRepository.existsByName(request.name)) {
+            log.info { "[ThemeService.createTheme] 테마 생성 실패(이름 중복): name=${request.name}" }
             throw ThemeException(ThemeErrorCode.THEME_NAME_DUPLICATED)
         }
 
         val theme: ThemeEntity = request.toEntity()
-        return themeRepository.save(theme).toResponse()
+        return themeRepository.save(theme)
+            .also { log.info { "[ThemeService.createTheme] 테마 생성 완료: themeId=${it.id}" } }
+            .toResponse()
     }
 
     @Transactional
     fun deleteTheme(id: Long) {
+        log.debug { "[ThemeService.deleteTheme] 테마 삭제 시작: themeId=$id" }
+
         if (themeRepository.isReservedTheme(id)) {
+            log.info { "[ThemeService.deleteTheme] 테마 삭제 실패(예약이 있는 테마): themeId=$id" }
             throw ThemeException(ThemeErrorCode.THEME_ALREADY_RESERVED)
         }
 
         themeRepository.deleteById(id)
+            .also { log.info { "[ThemeService.deleteTheme] 테마 삭제 완료: themeId=$id" } }
     }
 }