feat(ai): Ask Chat 예시 질문 10분 로테이션 적용

src/main/java/com/devkor/ifive/nadab/domain/askchat/api/AskChatSessionController.java

@@ -47,6 +47,7 @@ public class AskChatSessionController {
                     홈 진입만으로 새 채팅 세션을 생성하지 않습니다. </br>
                     사용자의 누적 답변 개수가 20개 이상인 경우에만 물어보기 홈을 조회할 수 있습니다. </br>
                     응답에는 남은 메시지 횟수, 사용자 닉네임, 보유 크리스탈 수, 예시 질문 목록을 포함합니다. </br>
+                    예시 질문은 사용자별로 10분 단위로 갱신되며 같은 시간 구간에는 동일하게 유지됩니다. </br>
                     히스토리 목록은 이 API에서 반환하지 않으며, 별도 히스토리 API를 사용해야 합니다.
                     """,
             security = @SecurityRequirement(name = "bearerAuth"),

src/main/java/com/devkor/ifive/nadab/domain/askchat/api/dto/response/AskChatHomeResponse.java

@@ -15,7 +15,7 @@ public record AskChatHomeResponse(
         @Schema(description = "사용자가 보유한 크리스탈 개수", example = "100")
         long crystalBalance,
 
-        @Schema(description = "홈 화면에 표시할 예시 질문 목록. 여러 주제 중 일부를 랜덤으로 제공합니다.")
+        @Schema(description = "홈 화면에 표시할 예시 질문 목록. 사용자별로 10분 단위로 갱신됩니다.")
         List<AskChatSampleQuestionResponse> sampleQuestions
 ) {
 }

src/main/java/com/devkor/ifive/nadab/domain/askchat/application/AskChatSessionService.java

@@ -4,6 +4,7 @@
 import com.devkor.ifive.nadab.domain.askchat.api.dto.response.AskChatQuestionSendResponse;
 import com.devkor.ifive.nadab.domain.askchat.api.dto.response.AskChatRemainingMessageCountResponse;
 import com.devkor.ifive.nadab.domain.askchat.api.dto.response.AskChatSampleQuestionResponse;
+import com.devkor.ifive.nadab.domain.askchat.application.helper.AskChatSampleQuestionSelector;
 import com.devkor.ifive.nadab.domain.askchat.core.entity.AskChatSampleQuestion;
 import com.devkor.ifive.nadab.domain.askchat.core.entity.AskChatSession;
 import com.devkor.ifive.nadab.domain.askchat.core.entity.AskChatWallet;
@@ -12,7 +13,6 @@
 import com.devkor.ifive.nadab.domain.askchat.core.repository.AskChatWalletRepository;
 import com.devkor.ifive.nadab.domain.dailyreport.core.repository.AnswerEntryRepository;
 import com.devkor.ifive.nadab.domain.user.core.entity.User;
-import com.devkor.ifive.nadab.domain.user.core.entity.InterestCode;
 import com.devkor.ifive.nadab.domain.user.core.repository.UserRepository;
 import com.devkor.ifive.nadab.domain.wallet.core.entity.UserWallet;
 import com.devkor.ifive.nadab.domain.wallet.core.repository.UserWalletRepository;
@@ -23,25 +23,20 @@
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.LinkedHashMap;
+import java.time.Instant;
 import java.util.List;
-import java.util.Map;
-import java.util.concurrent.ThreadLocalRandom;
-import java.util.stream.Collectors;
 
 @Service
 @RequiredArgsConstructor
 public class AskChatSessionService {
 
     public static final int MAX_TURN_COUNT = 15;
     public static final int MIN_ANSWER_COUNT_TO_USE_ASK_CHAT = 20;
-    private static final int HOME_SAMPLE_QUESTION_SIZE = 3;
 
     private final AskChatSessionRepository askChatSessionRepository;
     private final AskChatWalletRepository askChatWalletRepository;
     private final AskChatSampleQuestionRepository askChatSampleQuestionRepository;
+    private final AskChatSampleQuestionSelector askChatSampleQuestionSelector;
     private final UserWalletRepository userWalletRepository;
     private final UserRepository userRepository;
     private final AnswerEntryRepository answerEntryRepository;
@@ -61,7 +56,7 @@ public AskChatHomeResponse getHome(Long userId) {
                 askChatWallet.getTotalTurnBalance(),
                 user.getNickname(),
                 userWallet.getCrystalBalance(),
-                pickSampleQuestions()
+                selectSampleQuestions(userId)
         );
     }
 
@@ -92,27 +87,14 @@ private AskChatSession createSession(Long userId) {
         return askChatSessionRepository.save(AskChatSession.start(user));
     }
 
-    private List<AskChatSampleQuestionResponse> pickSampleQuestions() {
-        Map<InterestCode, List<AskChatSampleQuestion>> questionsByCategory = askChatSampleQuestionRepository
-                .findByActiveTrueOrderByDisplayOrderAsc()
-                .stream()
-                .collect(Collectors.groupingBy(
-                        AskChatSampleQuestion::getInterestCode,
-                        LinkedHashMap::new,
-                        Collectors.toList()
-                ));
-
-        List<InterestCode> categories = new ArrayList<>(questionsByCategory.keySet());
-        Collections.shuffle(categories);
+    private List<AskChatSampleQuestionResponse> selectSampleQuestions(Long userId) {
+        List<AskChatSampleQuestion> sampleQuestions = askChatSampleQuestionRepository
+                .findByActiveTrueOrderByDisplayOrderAsc();
 
-        return categories.stream()
-                .limit(HOME_SAMPLE_QUESTION_SIZE)
-                .map(category -> pickOne(questionsByCategory.get(category)))
+        return askChatSampleQuestionSelector
+                .select(userId, Instant.now(), sampleQuestions)
+                .stream()
                 .map(AskChatSampleQuestionResponse::from)
                 .toList();
     }
-
-    private AskChatSampleQuestion pickOne(List<AskChatSampleQuestion> sampleQuestions) {
-        return sampleQuestions.get(ThreadLocalRandom.current().nextInt(sampleQuestions.size()));
-    }
 }

src/main/java/com/devkor/ifive/nadab/domain/askchat/application/helper/AskChatSampleQuestionSelector.java

@@ -0,0 +1,94 @@
+package com.devkor.ifive.nadab.domain.askchat.application.helper;
+
+import com.devkor.ifive.nadab.domain.askchat.core.entity.AskChatSampleQuestion;
+import com.devkor.ifive.nadab.domain.user.core.entity.InterestCode;
+import org.springframework.stereotype.Component;
+
+import java.time.Duration;
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.EnumMap;
+import java.util.List;
+import java.util.Map;
+
+@Component
+public class AskChatSampleQuestionSelector {
+
+    private static final int SAMPLE_QUESTION_SIZE = 3;
+    private static final long ROTATION_INTERVAL_SECONDS = Duration.ofMinutes(10).toSeconds();
+    private static final long CATEGORY_SALT = 0x9E3779B97F4A7C15L;
+
+    public List<AskChatSampleQuestion> select(
+            Long userId,
+            Instant now,
+            List<AskChatSampleQuestion> sampleQuestions
+    ) {
+        Map<InterestCode, List<AskChatSampleQuestion>> questionsByCategory = groupByCategory(sampleQuestions);
+        if (questionsByCategory.isEmpty()) {
+            return List.of();
+        }
+
+        long rotationSlot = Math.floorDiv(now.getEpochSecond(), ROTATION_INTERVAL_SECONDS);
+        List<InterestCode> categories = orderedCategories(userId, questionsByCategory);
+        int categoryStartIndex = rotatedIndex(mix(userId), rotationSlot, categories.size());
+        int resultSize = Math.min(SAMPLE_QUESTION_SIZE, categories.size());
+
+        List<AskChatSampleQuestion> selectedQuestions = new ArrayList<>(resultSize);
+        for (int index = 0; index < resultSize; index++) {
+            InterestCode category = categories.get((categoryStartIndex + index) % categories.size());
+            List<AskChatSampleQuestion> categoryQuestions = questionsByCategory.get(category);
+            int questionIndex = rotatedIndex(
+                    mix(userId ^ (CATEGORY_SALT * (category.ordinal() + 1L))),
+                    rotationSlot,
+                    categoryQuestions.size()
+            );
+            selectedQuestions.add(categoryQuestions.get(questionIndex));
+        }
+
+        return List.copyOf(selectedQuestions);
+    }
+
+    private Map<InterestCode, List<AskChatSampleQuestion>> groupByCategory(
+            List<AskChatSampleQuestion> sampleQuestions
+    ) {
+        Map<InterestCode, List<AskChatSampleQuestion>> questionsByCategory =
+                new EnumMap<>(InterestCode.class);
+
+        for (AskChatSampleQuestion sampleQuestion : sampleQuestions) {
+            questionsByCategory
+                    .computeIfAbsent(sampleQuestion.getInterestCode(), ignored -> new ArrayList<>())
+                    .add(sampleQuestion);
+        }
+
+        Comparator<AskChatSampleQuestion> questionOrder = Comparator
+                .comparingInt(AskChatSampleQuestion::getDisplayOrder)
+                .thenComparing(AskChatSampleQuestion::getQuestion);
+        questionsByCategory.values().forEach(questions -> questions.sort(questionOrder));
+        return questionsByCategory;
+    }
+
+    private List<InterestCode> orderedCategories(
+            Long userId,
+            Map<InterestCode, List<AskChatSampleQuestion>> questionsByCategory
+    ) {
+        List<InterestCode> categories = new ArrayList<>(questionsByCategory.keySet());
+        categories.sort(Comparator
+                .comparingLong((InterestCode category) ->
+                        mix(userId ^ (CATEGORY_SALT * (category.ordinal() + 1L))))
+                .thenComparing(InterestCode::name));
+        return categories;
+    }
+
+    private int rotatedIndex(long base, long rotationSlot, int size) {
+        int baseIndex = Math.floorMod(base, size);
+        int slotOffset = Math.floorMod(rotationSlot, size);
+        return (baseIndex + slotOffset) % size;
+    }
+
+    private long mix(long value) {
+        value = (value ^ (value >>> 33)) * 0xff51afd7ed558ccdl;
+        value = (value ^ (value >>> 33)) * 0xc4ceb9fe1a85ec53l;
+        return value ^ (value >>> 33);
+    }
+}

src/test/java/com/devkor/ifive/nadab/domain/askchat/application/AskChatSessionServiceTest.java

@@ -5,6 +5,7 @@
 import com.devkor.ifive.nadab.domain.askchat.core.entity.AskChatSessionStatus;
 import com.devkor.ifive.nadab.domain.askchat.core.entity.AskChatWallet;
 import com.devkor.ifive.nadab.domain.askchat.api.dto.response.AskChatQuestionSendResponse;
+import com.devkor.ifive.nadab.domain.askchat.application.helper.AskChatSampleQuestionSelector;
 import com.devkor.ifive.nadab.domain.askchat.core.repository.AskChatSampleQuestionRepository;
 import com.devkor.ifive.nadab.domain.askchat.core.repository.AskChatSessionRepository;
 import com.devkor.ifive.nadab.domain.askchat.core.repository.AskChatWalletRepository;
@@ -24,6 +25,7 @@
 import org.mockito.Mock;
 import org.mockito.junit.jupiter.MockitoExtension;
 
+import java.time.Instant;
 import java.time.OffsetDateTime;
 import java.time.ZoneOffset;
 import java.util.List;
@@ -32,6 +34,8 @@
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.ArgumentMatchers.same;
 import static org.mockito.Mockito.lenient;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.never;
@@ -51,6 +55,9 @@ class AskChatSessionServiceTest {
     @Mock
     private AskChatSampleQuestionRepository askChatSampleQuestionRepository;
 
+    @Mock
+    private AskChatSampleQuestionSelector askChatSampleQuestionSelector;
+
     @Mock
     private UserWalletRepository userWalletRepository;
 
@@ -71,6 +78,7 @@ void setUp() {
                 askChatSessionRepository,
                 askChatWalletRepository,
                 askChatSampleQuestionRepository,
+                askChatSampleQuestionSelector,
                 userWalletRepository,
                 userRepository,
                 answerEntryRepository,
@@ -86,11 +94,23 @@ void getHome_returns_home_display_data_without_creating_session() {
         when(userRepository.findById(1L)).thenReturn(Optional.of(user));
         when(askChatWalletRepository.findByUserId(1L)).thenReturn(Optional.of(AskChatWallet.create(user, 2, 7)));
         when(userWalletRepository.findByUserId(1L)).thenReturn(Optional.of(UserWallet.create(user, 100L)));
-        when(askChatSampleQuestionRepository.findByActiveTrueOrderByDisplayOrderAsc()).thenReturn(List.of(
+        List<AskChatSampleQuestion> sampleQuestions = List.of(
                 AskChatSampleQuestion.create(InterestCode.VALUES, "나는 어떤 사람이야?", 1),
                 AskChatSampleQuestion.create(InterestCode.PREFERENCE, "내가 좋아하는 것들의 공통점은 뭐야?", 2),
                 AskChatSampleQuestion.create(InterestCode.RELATIONSHIP, "어떤 사람과 잘 맞을까?", 3)
-        ));
+        );
+        List<AskChatSampleQuestion> selectedQuestions = List.of(
+                sampleQuestions.get(2),
+                sampleQuestions.get(0),
+                sampleQuestions.get(1)
+        );
+        when(askChatSampleQuestionRepository.findByActiveTrueOrderByDisplayOrderAsc())
+                .thenReturn(sampleQuestions);
+        when(askChatSampleQuestionSelector.select(
+                eq(1L),
+                any(Instant.class),
+                same(sampleQuestions)
+        )).thenReturn(selectedQuestions);
 
         var response = service.getHome(1L);
 
@@ -100,7 +120,12 @@ void getHome_returns_home_display_data_without_creating_session() {
         assertThat(response.sampleQuestions()).hasSize(3);
         assertThat(response.sampleQuestions())
                 .extracting("category")
-                .containsExactlyInAnyOrder("VALUES", "PREFERENCE", "RELATIONSHIP");
+                .containsExactly("RELATIONSHIP", "VALUES", "PREFERENCE");
+        verify(askChatSampleQuestionSelector).select(
+                eq(1L),
+                any(Instant.class),
+                same(sampleQuestions)
+        );
         verify(askChatSessionRepository, never()).save(any());
     }
 
@@ -115,6 +140,7 @@ void getHome_rejects_when_answer_count_is_less_than_minimum() {
         verifyNoInteractions(askChatWalletRepository);
         verifyNoInteractions(userWalletRepository);
         verifyNoInteractions(askChatSampleQuestionRepository);
+        verifyNoInteractions(askChatSampleQuestionSelector);
         verify(askChatSessionRepository, never()).save(any());
         verifyNoInteractions(askChatMessageCommandService);
     }

src/test/java/com/devkor/ifive/nadab/domain/askchat/application/helper/AskChatSampleQuestionSelectorTest.java

@@ -0,0 +1,100 @@
+package com.devkor.ifive.nadab.domain.askchat.application.helper;
+
+import com.devkor.ifive.nadab.domain.askchat.core.entity.AskChatSampleQuestion;
+import com.devkor.ifive.nadab.domain.user.core.entity.InterestCode;
+import org.junit.jupiter.api.Test;
+
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class AskChatSampleQuestionSelectorTest {
+
+    private final AskChatSampleQuestionSelector selector = new AskChatSampleQuestionSelector();
+
+    @Test
+    void select_returns_same_questions_within_same_ten_minute_slot() {
+        List<AskChatSampleQuestion> questions = questionsForAllCategories();
+
+        var first = selector.select(1L, Instant.parse("2026-08-15T00:00:00Z"), questions);
+        var last = selector.select(1L, Instant.parse("2026-08-15T00:09:59Z"), questions);
+
+        assertThat(last).containsExactlyElementsOf(first);
+    }
+
+    @Test
+    void select_rotates_questions_when_ten_minute_slot_changes() {
+        List<AskChatSampleQuestion> questions = questionsForAllCategories();
+
+        var before = selector.select(1L, Instant.parse("2026-08-15T00:09:59Z"), questions);
+        var after = selector.select(1L, Instant.parse("2026-08-15T00:10:00Z"), questions);
+
+        assertThat(after).isNotEqualTo(before);
+        assertThat(after)
+                .extracting(AskChatSampleQuestion::getInterestCode)
+                .doesNotHaveDuplicates();
+    }
+
+    @Test
+    void select_distributes_questions_by_user() {
+        List<AskChatSampleQuestion> questions = questionsForAllCategories();
+        Instant now = Instant.parse("2026-08-15T00:05:00Z");
+
+        var firstUser = selector.select(1L, now, questions);
+        var secondUser = selector.select(2L, now, questions);
+
+        assertThat(secondUser).isNotEqualTo(firstUser);
+    }
+
+    @Test
+    void select_is_independent_of_input_order() {
+        List<AskChatSampleQuestion> questions = questionsForAllCategories();
+        List<AskChatSampleQuestion> reversedQuestions = new ArrayList<>(questions);
+        Collections.reverse(reversedQuestions);
+        Instant now = Instant.parse("2026-08-15T00:05:00Z");
+
+        var originalOrder = selector.select(1L, now, questions);
+        var reversedOrder = selector.select(1L, now, reversedQuestions);
+
+        assertThat(reversedOrder).containsExactlyElementsOf(originalOrder);
+    }
+
+    @Test
+    void select_returns_available_categories_when_fewer_than_three_exist() {
+        List<AskChatSampleQuestion> questions = List.of(
+                question(InterestCode.PREFERENCE, "취향 질문", 2),
+                question(InterestCode.VALUES, "가치관 질문", 1)
+        );
+
+        var selected = selector.select(1L, Instant.parse("2026-08-15T00:05:00Z"), questions);
+
+        assertThat(selected).hasSize(2);
+        assertThat(selected)
+                .extracting(AskChatSampleQuestion::getInterestCode)
+                .containsExactlyInAnyOrder(InterestCode.PREFERENCE, InterestCode.VALUES);
+    }
+
+    @Test
+    void select_returns_empty_list_when_no_questions_exist() {
+        var selected = selector.select(1L, Instant.parse("2026-08-15T00:05:00Z"), List.of());
+
+        assertThat(selected).isEmpty();
+    }
+
+    private List<AskChatSampleQuestion> questionsForAllCategories() {
+        List<AskChatSampleQuestion> questions = new ArrayList<>();
+        int displayOrder = 1;
+        for (InterestCode category : InterestCode.values()) {
+            questions.add(question(category, category.name() + " 질문 A", displayOrder++));
+            questions.add(question(category, category.name() + " 질문 B", displayOrder++));
+        }
+        return questions;
+    }
+
+    private AskChatSampleQuestion question(InterestCode category, String question, int displayOrder) {
+        return AskChatSampleQuestion.create(category, question, displayOrder);
+    }
+}