feat(gift): 신청번호 생성기를 추가한다

src/main/kotlin/kr/co/vividnext/sodalive/v2/gift/application/GiftApplicationNoGenerator.kt

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+package kr.co.vividnext.sodalive.v2.gift.application
+
+import kr.co.vividnext.sodalive.common.SodaException
+import kr.co.vividnext.sodalive.v2.gift.adapter.out.persistence.GiftApplicationNoSequence
+import kr.co.vividnext.sodalive.v2.gift.adapter.out.persistence.GiftApplicationNoSequenceRepository
+import org.springframework.dao.DataIntegrityViolationException
+import org.springframework.stereotype.Service
+import org.springframework.transaction.PlatformTransactionManager
+import org.springframework.transaction.support.TransactionTemplate
+import java.time.LocalDateTime
+import java.time.ZoneId
+import java.time.format.DateTimeFormatter
+
+@Service
+class GiftApplicationNoGenerator(
+    private val repository: GiftApplicationNoSequenceRepository,
+    transactionManager: PlatformTransactionManager
+) {
+    private val transactionTemplate = TransactionTemplate(transactionManager)
+
+    fun generate(now: LocalDateTime = LocalDateTime.now(SEOUL_ZONE)): String {
+        val sequenceDate = now.format(DATE_FORMATTER)
+        for (attempt in 1..MAX_RETRY_COUNT) {
+            try {
+                return transactionTemplate.execute {
+                    val sequence = repository.findBySequenceDateForUpdate(sequenceDate)
+                        ?: repository.saveAndFlush(GiftApplicationNoSequence(sequenceDate = sequenceDate, lastSequence = 0))
+                    sequence.lastSequence += 1
+                    "G$sequenceDate${sequence.lastSequence.toString().padStart(6, '0')}"
+                } ?: throw SodaException(messageKey = "common.error.invalid_request")
+            } catch (_: DataIntegrityViolationException) {
+                if (attempt == MAX_RETRY_COUNT) throw SodaException(messageKey = "gift.application_no.generate_failed")
+            }
+        }
+        throw SodaException(messageKey = "gift.application_no.generate_failed")
+    }
+
+    companion object {
+        private val SEOUL_ZONE = ZoneId.of("Asia/Seoul")
+        private val DATE_FORMATTER = DateTimeFormatter.ofPattern("yyyyMMdd")
+        private const val MAX_RETRY_COUNT = 3
+    }
+}

src/test/kotlin/kr/co/vividnext/sodalive/v2/gift/application/GiftApplicationNoGeneratorTest.kt

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+package kr.co.vividnext.sodalive.v2.gift.application
+
+import kr.co.vividnext.sodalive.configs.QueryDslConfig
+import kr.co.vividnext.sodalive.v2.gift.adapter.out.persistence.GiftApplicationNoSequenceRepository
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.BeforeEach
+import org.junit.jupiter.api.DisplayName
+import org.junit.jupiter.api.Test
+import org.springframework.beans.factory.annotation.Autowired
+import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest
+import org.springframework.context.annotation.Import
+import org.springframework.transaction.PlatformTransactionManager
+import java.time.LocalDateTime
+import java.util.concurrent.Callable
+import java.util.concurrent.Executors
+
+@DataJpaTest(
+    properties = [
+        "spring.cache.type=none",
+        "spring.datasource.url=jdbc:h2:mem:testdb;MODE=MySQL;NON_KEYWORDS=VALUE"
+    ]
+)
+@Import(QueryDslConfig::class)
+@DisplayName("선물 신청번호 채번 테스트")
+class GiftApplicationNoGeneratorTest @Autowired constructor(
+    private val repository: GiftApplicationNoSequenceRepository,
+    private val transactionManager: PlatformTransactionManager
+) {
+    @BeforeEach
+    fun setUp() {
+        repository.deleteAll()
+    }
+
+    @Test
+    @DisplayName("같은 날짜 신청번호를 순서대로 발급한다")
+    fun shouldGenerateSequentialApplicationNoByDate() {
+        val generator = GiftApplicationNoGenerator(repository, transactionManager)
+        val now = LocalDateTime.of(2026, 9, 29, 12, 0)
+
+        val first = generator.generate(now)
+        val second = generator.generate(now)
+
+        assertEquals("G20260929000001", first)
+        assertEquals("G20260929000002", second)
+    }
+
+    @Test
+    @DisplayName("병렬 발급 결과는 모두 중복되지 않는다")
+    fun shouldGenerateUniqueApplicationNoConcurrently() {
+        val generator = GiftApplicationNoGenerator(repository, transactionManager)
+        val now = LocalDateTime.of(2026, 9, 29, 12, 0)
+        val executor = Executors.newFixedThreadPool(4)
+
+        val applicationNos = try {
+            executor.invokeAll(
+                (1..10).map {
+                    Callable { generator.generate(now) }
+                }
+            ).map { it.get() }
+        } finally {
+            executor.shutdownNow()
+        }
+
+        assertEquals(10, applicationNos.toSet().size)
+        assertEquals("G20260929000001", applicationNos.minOrNull())
+        assertEquals("G20260929000010", applicationNos.maxOrNull())
+    }
+}