feat(ranking): 주간 랭킹 기간 정책을 추가한다

src/main/kotlin/kr/co/vividnext/sodalive/v2/ranking/domain/CreatorRankingPeriodPolicy.kt

@@ -0,0 +1,42 @@
+package kr.co.vividnext.sodalive.v2.ranking.domain
+
+import java.time.DayOfWeek
+import java.time.LocalDateTime
+import java.time.ZoneId
+import java.time.ZonedDateTime
+import java.time.temporal.TemporalAdjusters
+
+class CreatorRankingPeriodPolicy {
+    fun resolveLastCompletedWeek(now: ZonedDateTime): CreatorRankingPeriod {
+        val nowKst = now.withZoneSameInstant(KST_ZONE)
+        val thisWeekMonday = nowKst.toLocalDate()
+            .with(TemporalAdjusters.previousOrSame(DayOfWeek.MONDAY))
+            .atStartOfDay()
+        return CreatorRankingPeriod(
+            startInclusiveKst = thisWeekMonday.minusWeeks(1),
+            endExclusiveKst = thisWeekMonday
+        )
+    }
+
+    fun toUtcRange(period: CreatorRankingPeriod): CreatorRankingUtcRange {
+        return CreatorRankingUtcRange(
+            startInclusiveUtc = period.startInclusiveKst.atZone(KST_ZONE).withZoneSameInstant(UTC_ZONE).toLocalDateTime(),
+            endExclusiveUtc = period.endExclusiveKst.atZone(KST_ZONE).withZoneSameInstant(UTC_ZONE).toLocalDateTime()
+        )
+    }
+
+    companion object {
+        private val KST_ZONE: ZoneId = ZoneId.of("Asia/Seoul")
+        private val UTC_ZONE: ZoneId = ZoneId.of("UTC")
+    }
+}
+
+data class CreatorRankingPeriod(
+    val startInclusiveKst: LocalDateTime,
+    val endExclusiveKst: LocalDateTime
+)
+
+data class CreatorRankingUtcRange(
+    val startInclusiveUtc: LocalDateTime,
+    val endExclusiveUtc: LocalDateTime
+)

src/test/kotlin/kr/co/vividnext/sodalive/v2/ranking/domain/CreatorRankingPeriodPolicyTest.kt

@@ -0,0 +1,59 @@
+package kr.co.vividnext.sodalive.v2.ranking.domain
+
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.DisplayName
+import org.junit.jupiter.api.Test
+import java.time.LocalDateTime
+import java.time.ZoneId
+import java.time.ZonedDateTime
+
+class CreatorRankingPeriodPolicyTest {
+    private val policy = CreatorRankingPeriodPolicy()
+
+    @Test
+    @DisplayName("월요일 KST 기준 지난 주 월요일 00시 이상 이번 주 월요일 00시 미만 기간을 산출한다")
+    fun shouldResolveLastCompletedWeekByKstMonday() {
+        val now = ZonedDateTime.of(2026, 6, 8, 6, 0, 0, 0, ZoneId.of("Asia/Seoul"))
+
+        val period = policy.resolveLastCompletedWeek(now)
+
+        assertEquals(LocalDateTime.of(2026, 6, 1, 0, 0), period.startInclusiveKst)
+        assertEquals(LocalDateTime.of(2026, 6, 8, 0, 0), period.endExclusiveKst)
+    }
+
+    @Test
+    @DisplayName("기간 산출은 서버 timezone UTC와 무관하게 KST 기준으로 계산한다")
+    fun shouldResolveLastCompletedWeekIndependentOfServerTimezone() {
+        val now = ZonedDateTime.of(2026, 6, 7, 21, 0, 0, 0, ZoneId.of("UTC"))
+
+        val period = policy.resolveLastCompletedWeek(now)
+
+        assertEquals(LocalDateTime.of(2026, 6, 1, 0, 0), period.startInclusiveKst)
+        assertEquals(LocalDateTime.of(2026, 6, 8, 0, 0), period.endExclusiveKst)
+    }
+
+    @Test
+    @DisplayName("연도 경계를 넘어도 KST 기준 지난 완료 주차를 산출한다")
+    fun shouldResolveLastCompletedWeekAcrossYearBoundary() {
+        val now = ZonedDateTime.of(2026, 1, 1, 12, 0, 0, 0, ZoneId.of("Asia/Seoul"))
+
+        val period = policy.resolveLastCompletedWeek(now)
+
+        assertEquals(LocalDateTime.of(2025, 12, 22, 0, 0), period.startInclusiveKst)
+        assertEquals(LocalDateTime.of(2025, 12, 29, 0, 0), period.endExclusiveKst)
+    }
+
+    @Test
+    @DisplayName("KST 기간은 DB 조회용 UTC LocalDateTime 이상/미만 조건으로 변환한다")
+    fun shouldConvertKstPeriodToUtcRange() {
+        val period = CreatorRankingPeriod(
+            startInclusiveKst = LocalDateTime.of(2026, 6, 1, 0, 0),
+            endExclusiveKst = LocalDateTime.of(2026, 6, 8, 0, 0)
+        )
+
+        val utcRange = policy.toUtcRange(period)
+
+        assertEquals(LocalDateTime.of(2026, 5, 31, 15, 0), utcRange.startInclusiveUtc)
+        assertEquals(LocalDateTime.of(2026, 6, 7, 15, 0), utcRange.endExclusiveUtc)
+    }
+}