src/main/kotlin/kr/co/vividnext/sodalive/v2/recommendation/application/HomeRecommendationQueryService.kt

@@ -1,6 +1,7 @@
 package kr.co.vividnext.sodalive.v2.recommendation.application
 
 import kr.co.vividnext.sodalive.v2.common.domain.CreatorActivityType
+import kr.co.vividnext.sodalive.v2.recommendation.domain.RecommendationSnapshotWindowPolicy
 import kr.co.vividnext.sodalive.v2.recommendation.domain.RecommendedSectionType
 import kr.co.vividnext.sodalive.v2.recommendation.port.out.HomeAiCharacterRecommendationRecord
 import kr.co.vividnext.sodalive.v2.recommendation.port.out.HomeBannerRecommendationRecord
@@ -13,8 +14,10 @@ import kr.co.vividnext.sodalive.v2.recommendation.port.out.HomeRecommendationQue
 import kr.co.vividnext.sodalive.v2.recommendation.port.out.RecentDebutCreatorRecord
 import kr.co.vividnext.sodalive.v2.recommendation.port.out.RecentlyActiveCreatorRecord
 import kr.co.vividnext.sodalive.v2.recommendation.port.out.RecommendationSnapshotPort
+import kr.co.vividnext.sodalive.v2.recommendation.port.out.RecommendationSnapshotRecord
 import org.springframework.stereotype.Service
 import org.springframework.transaction.annotation.Transactional
+import java.time.Clock
 import java.time.LocalDateTime
 
 @Service
@@ -22,8 +25,12 @@ import java.time.LocalDateTime
 class HomeRecommendationQueryService(
     private val queryPort: HomeRecommendationQueryPort,
     private val snapshotPort: RecommendationSnapshotPort,
-    private val aiCharacterSnapshotFallbackService: AiCharacterSnapshotFallbackPort? = null
+    private val aiCharacterSnapshotFallbackService: AiCharacterSnapshotFallbackPort? = null,
+    private val cheerCreatorSnapshotFallbackService: CheerCreatorSnapshotFallbackPort? = null,
+    private val clock: Clock = Clock.systemUTC()
 ) {
+    private val snapshotWindowPolicy = RecommendationSnapshotWindowPolicy()
+
     fun findLiveRecommendations(
         offset: Long = 0,
         limit: Int = DEFAULT_LIVE_LIMIT,
@@ -95,13 +102,28 @@ class HomeRecommendationQueryService(
         limit: Int = DEFAULT_CHEER_CREATOR_LIMIT,
         memberId: Long? = null
     ): List<HomeCheerCreatorRecommendationRecord> {
-        val snapshots = snapshotPort.findLatestSnapshots(RecommendedSectionType.CHEER_CREATOR).take(CHEER_CREATOR_CANDIDATE_LIMIT)
+        val snapshots = findCheerCreatorSnapshotsWithFallback()
         val detailsById = queryPort.findCheerCreatorRecommendationDetails(snapshots.map { it.targetId }, memberId)
             .associateBy { it.creatorId }
 
         return snapshots.mapNotNull { detailsById[it.targetId] }.take(limit)
     }
 
+    private fun findCheerCreatorSnapshotsWithFallback(): List<RecommendationSnapshotRecord> {
+        val nowUtc = LocalDateTime.now(clock)
+        val snapshotAt = snapshotWindowPolicy.previousKstDayUtcWindow(nowUtc).snapshotAt
+        val snapshots = snapshotPort.findSnapshots(
+            RecommendedSectionType.CHEER_CREATOR,
+            snapshotAt,
+            limit = CHEER_CREATOR_CANDIDATE_LIMIT
+        )
+        if (snapshots.isNotEmpty()) return snapshots
+        if (snapshotPort.existsSnapshot(RecommendedSectionType.CHEER_CREATOR, snapshotAt)) return emptyList()
+        return cheerCreatorSnapshotFallbackService
+            ?.refreshCheerCreatorIfMissing(offset = 0, limit = CHEER_CREATOR_CANDIDATE_LIMIT, nowUtc = nowUtc)
+            .orEmpty()
+    }
+
     fun findPopularCommunityRecommendations(
         limit: Int = DEFAULT_POPULAR_COMMUNITY_LIMIT,
         memberId: Long? = null,

src/test/kotlin/kr/co/vividnext/sodalive/v2/recommendation/application/HomeRecommendationQueryServiceTest.kt

@@ -18,7 +18,10 @@ import kr.co.vividnext.sodalive.v2.recommendation.port.out.RecommendationSnapsho
 import org.junit.jupiter.api.Assertions.assertEquals
 import org.junit.jupiter.api.DisplayName
 import org.junit.jupiter.api.Test
+import java.time.Clock
+import java.time.Instant
 import java.time.LocalDateTime
+import java.time.ZoneOffset
 
 class HomeRecommendationQueryServiceTest {
     private val port = FakeHomeRecommendationQueryPort()
@@ -280,7 +283,14 @@ class HomeRecommendationQueryServiceTest {
     @Test
     @DisplayName("최근 응원 크리에이터 추천은 최신 스냅샷 8명을 기준으로 닉네임과 프로필을 조립한다")
     fun shouldFindCheerCreatorsFromLatestSnapshotsWithLimitAndDetails() {
-        val snapshotAt = LocalDateTime.of(2026, 5, 29, 23, 59, 59)
+        val fallback = FakeCheerCreatorSnapshotFallbackPort(emptyList())
+        val service = HomeRecommendationQueryService(
+            port,
+            snapshotPort,
+            cheerCreatorSnapshotFallbackService = fallback,
+            clock = fixedClock()
+        )
+        val snapshotAt = LocalDateTime.of(2026, 7, 9, 14, 59, 59)
         snapshotPort.replaceSnapshots(
             RecommendedSectionType.CHEER_CREATOR,
             snapshotAt,
@@ -303,12 +313,104 @@ class HomeRecommendationQueryServiceTest {
 
         val creators = service.findCheerCreatorRecommendations(memberId = 104L)
 
+        assertEquals(null, fallback.offset)
+        assertEquals(null, fallback.limit)
         assertEquals((1L..9L).toList(), port.cheerCreatorDetailIds)
         assertEquals(104L, port.cheerCreatorMemberId)
         assertEquals(listOf(1L, 2L), creators.map { it.creatorId })
         assertEquals(listOf("creator-1", "creator-2"), creators.map { it.creatorNickname })
     }
 
+    @Test
+    @DisplayName("최근 응원 크리에이터 추천은 최신 스냅샷이 없으면 fallback refresh 후 스냅샷 상세를 조립한다")
+    fun shouldFindCheerCreatorsAfterFallbackWhenLatestSnapshotsDoNotExist() {
+        val fallback = FakeCheerCreatorSnapshotFallbackPort(
+            listOf(snapshot(RecommendedSectionType.CHEER_CREATOR, 10L, 10.0, LocalDateTime.of(2026, 7, 9, 14, 59, 59)))
+        )
+        val service = HomeRecommendationQueryService(
+            port,
+            snapshotPort,
+            cheerCreatorSnapshotFallbackService = fallback,
+            clock = fixedClock()
+        )
+        port.cheerCreatorDetails = listOf(
+            HomeCheerCreatorRecommendationRecord(
+                creatorId = 10L,
+                creatorNickname = "fallback-creator",
+                creatorProfileImage = null
+            )
+        )
+
+        val creators = service.findCheerCreatorRecommendations(memberId = 104L)
+
+        assertEquals(0L, fallback.offset)
+        assertEquals(16, fallback.limit)
+        assertEquals(LocalDateTime.of(2026, 7, 9, 21, 0), fallback.nowUtc)
+        assertEquals(listOf(10L), port.cheerCreatorDetailIds)
+        assertEquals(listOf(10L), creators.map { it.creatorId })
+    }
+
+    @Test
+    @DisplayName("최근 응원 크리에이터 추천은 오래된 스냅샷만 있으면 fallback refresh를 호출한다")
+    fun shouldFallbackWhenOnlyStaleCheerCreatorSnapshotsExist() {
+        val fallback = FakeCheerCreatorSnapshotFallbackPort(
+            listOf(snapshot(RecommendedSectionType.CHEER_CREATOR, 10L, 10.0, LocalDateTime.of(2026, 7, 9, 14, 59, 59)))
+        )
+        val service = HomeRecommendationQueryService(
+            port,
+            snapshotPort,
+            cheerCreatorSnapshotFallbackService = fallback,
+            clock = fixedClock()
+        )
+        val staleSnapshotAt = LocalDateTime.of(2026, 7, 8, 14, 59, 59)
+        snapshotPort.replaceSnapshots(
+            RecommendedSectionType.CHEER_CREATOR,
+            staleSnapshotAt,
+            listOf(snapshot(RecommendedSectionType.CHEER_CREATOR, 99L, 99.0, staleSnapshotAt))
+        )
+        port.cheerCreatorDetails = listOf(
+            HomeCheerCreatorRecommendationRecord(
+                creatorId = 10L,
+                creatorNickname = "fallback-creator",
+                creatorProfileImage = null
+            )
+        )
+
+        val creators = service.findCheerCreatorRecommendations(memberId = 104L)
+
+        assertEquals(0L, fallback.offset)
+        assertEquals(16, fallback.limit)
+        assertEquals(LocalDateTime.of(2026, 7, 9, 21, 0), fallback.nowUtc)
+        assertEquals(listOf(10L), port.cheerCreatorDetailIds)
+        assertEquals(listOf(10L), creators.map { it.creatorId })
+    }
+
+    @Test
+    @DisplayName("최근 응원 크리에이터 추천은 빈 스냅샷 refresh 완료 marker가 있으면 fallback refresh를 반복하지 않는다")
+    fun shouldNotFallbackWhenEmptyCheerCreatorSnapshotCycleExists() {
+        val fallback = FakeCheerCreatorSnapshotFallbackPort(
+            listOf(snapshot(RecommendedSectionType.CHEER_CREATOR, 99L, 99.0, LocalDateTime.of(2026, 7, 9, 14, 59, 59)))
+        )
+        val service = HomeRecommendationQueryService(
+            port,
+            snapshotPort,
+            cheerCreatorSnapshotFallbackService = fallback,
+            clock = fixedClock()
+        )
+        snapshotPort.replaceSnapshots(
+            RecommendedSectionType.CHEER_CREATOR,
+            LocalDateTime.of(2026, 7, 9, 14, 59, 59),
+            emptyList()
+        )
+
+        val creators = service.findCheerCreatorRecommendations(memberId = 104L)
+
+        assertEquals(null, fallback.offset)
+        assertEquals(null, fallback.limit)
+        assertEquals(emptyList<Long>(), port.cheerCreatorDetailIds)
+        assertEquals(emptyList<HomeCheerCreatorRecommendationRecord>(), creators)
+    }
+
     @Test
     @DisplayName("인기 커뮤니티 추천은 최신 스냅샷 10개를 기준으로 크리에이터 중복을 제거하고 상세를 조립한다")
     fun shouldFindPopularCommunitiesFromLatestSnapshotsWithLimitDetailsAndCreatorUniqueness() {
@@ -861,7 +963,7 @@ class HomeRecommendationQueryServiceTest {
 
         override fun findCheerCreatorSnapshots(
             windowStart: LocalDateTime,
-            snapshotAt: LocalDateTime,
+            windowEndExclusive: LocalDateTime,
             limit: Int
         ): List<RecommendationSnapshotRecord> = emptyList()
 
@@ -931,17 +1033,35 @@ private class FakeHomeRecommendationSnapshotPort : RecommendationSnapshotPort {
         return all.drop(offset.toInt()).take(limit)
     }
 
+    override fun findSnapshots(
+        sectionType: RecommendedSectionType,
+        snapshotAt: LocalDateTime,
+        offset: Long,
+        limit: Int
+    ): List<RecommendationSnapshotRecord> {
+        val all = snapshots
+            .filter { it.sectionType == sectionType && it.snapshotAt == snapshotAt && it.targetId != 0L }
+            .sortedWith(compareByDescending<RecommendationSnapshotRecord> { it.score }.thenBy { it.randomTieBreaker })
+
+        if (offset == 0L && limit == Int.MAX_VALUE) return all
+        return all.drop(offset.toInt()).take(limit)
+    }
+
     override fun existsLatestSnapshot(sectionType: RecommendedSectionType): Boolean {
         return snapshots.any { it.sectionType == sectionType }
     }
 
+    override fun existsSnapshot(sectionType: RecommendedSectionType, snapshotAt: LocalDateTime): Boolean {
+        return snapshots.any { it.sectionType == sectionType && it.snapshotAt == snapshotAt }
+    }
+
     override fun replaceSnapshots(
         sectionType: RecommendedSectionType,
         snapshotAt: LocalDateTime,
         newSnapshots: List<RecommendationSnapshotRecord>
     ) {
-        if (newSnapshots.isEmpty() && sectionType == RecommendedSectionType.AI_CHARACTER) {
+        if (newSnapshots.isEmpty() && supportsEmptySnapshotMarker(sectionType)) {
-            snapshots.removeIf { it.sectionType == sectionType }
+            snapshots.removeIf { it.sectionType == sectionType && it.snapshotAt == snapshotAt }
             snapshots.add(snapshot(sectionType, targetId = 0L, score = 0.0, snapshotAt = snapshotAt))
             return
         }
@@ -949,6 +1069,33 @@ private class FakeHomeRecommendationSnapshotPort : RecommendationSnapshotPort {
         snapshots.removeIf { it.sectionType == sectionType && it.snapshotAt == snapshotAt }
         snapshots.addAll(newSnapshots)
     }
+
+    private fun supportsEmptySnapshotMarker(sectionType: RecommendedSectionType): Boolean {
+        return sectionType == RecommendedSectionType.AI_CHARACTER || sectionType == RecommendedSectionType.CHEER_CREATOR
+    }
+}
+
+private fun fixedClock(): Clock {
+    return Clock.fixed(Instant.parse("2026-07-09T21:00:00Z"), ZoneOffset.UTC)
+}
+
+private class FakeCheerCreatorSnapshotFallbackPort(
+    private val snapshots: List<RecommendationSnapshotRecord>
+) : CheerCreatorSnapshotFallbackPort {
+    var offset: Long? = null
+    var limit: Int? = null
+    var nowUtc: LocalDateTime? = null
+
+    override fun refreshCheerCreatorIfMissing(
+        offset: Long,
+        limit: Int,
+        nowUtc: LocalDateTime
+    ): List<RecommendationSnapshotRecord> {
+        this.offset = offset
+        this.limit = limit
+        this.nowUtc = nowUtc
+        return snapshots
+    }
 }
 
 private class FakeAiCharacterSnapshotFallbackPort(