feat: 스팟별 '이 시간대 자주 오는 견종' 통계 API

체크인 이력(check_ins)에서 현재와 같은 요일·시간대 방문을 집계해 상위 견종 반환.
GET /api/spots/{id}/frequent-breeds. 집계는 Java(요일/시간대, KST) — H2/Postgres 공용.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/main/java/com/dog/dognation/api/SpotController.java

@@ -1,6 +1,7 @@
 package com.dog.dognation.api;
 
 import com.dog.dognation.api.dto.SpotDtos.AiMateResponse;
+import com.dog.dognation.api.dto.SpotDtos.FrequentBreedsResponse;
 import com.dog.dognation.api.dto.SpotDtos.CheckInRequest;
 import com.dog.dognation.api.dto.SpotDtos.CheckInResponse;
 import com.dog.dognation.api.dto.SpotDtos.MateResponse;
@@ -62,6 +63,12 @@ public class SpotController {
         return mateAiService.compatibleMates(id, dogId);
     }
 
+    /** 현재 요일·시간대에 이 스팟에 자주 오는 견종(통계) */
+    @GetMapping("/{id}/frequent-breeds")
+    public FrequentBreedsResponse frequentBreeds(@PathVariable Long id) {
+        return spotService.frequentBreeds(id);
+    }
+
     /** 스팟 한줄평 목록 */
     @GetMapping("/{id}/reviews")
     public List<ReviewResponse> reviews(@PathVariable Long id) {

src/main/java/com/dog/dognation/api/dto/SpotDtos.java

@@ -7,6 +7,7 @@ import com.dog.dognation.domain.spot.SpotReview;
 import jakarta.validation.constraints.NotNull;
 
 import java.time.OffsetDateTime;
+import java.util.List;
 
 /** 스팟 관련 요청/응답 DTO 모음. */
 public final class SpotDtos {
@@ -30,6 +31,10 @@ public final class SpotDtos {
     public record AiMateResponse(Long dogId, String name, String breed, int score, String reason) {
     }
 
+    /** 현재 요일·시간대 기준, 이 스팟에 자주 오는 견종(빈도 내림차순). */
+    public record FrequentBreedsResponse(List<String> breeds) {
+    }
+
     public record ReviewResponse(Long id, String tag, String content, OffsetDateTime createdAt) {
         public static ReviewResponse from(SpotReview r) {
             return new ReviewResponse(r.getId(), r.getTag(), r.getContent(), r.getCreatedAt());

src/main/java/com/dog/dognation/domain/spot/CheckIn.java

@@ -56,6 +56,10 @@ public class CheckIn {
         return dogId;
     }
 
+    public OffsetDateTime getCheckedInAt() {
+        return checkedInAt;
+    }
+
     public OffsetDateTime getExpiresAt() {
         return expiresAt;
     }

src/main/java/com/dog/dognation/domain/spot/CheckInRepository.java

@@ -10,4 +10,7 @@ public interface CheckInRepository extends JpaRepository<CheckIn, Long> {
     /** 스팟에 현재 유효한(만료 전) 체크인 목록. */
     List<CheckIn> findBySpotIdAndExpiresAtAfterOrderByCheckedInAtDesc(
             Long spotId, OffsetDateTime now);
+
+    /** 통계용: 스팟의 특정 시점 이후 체크인 전체(요일/시간대 집계에 사용). */
+    List<CheckIn> findBySpotIdAndCheckedInAtAfter(Long spotId, OffsetDateTime since);
 }

src/main/java/com/dog/dognation/domain/spot/SpotService.java

@@ -1,12 +1,16 @@
 package com.dog.dognation.domain.spot;
 
+import com.dog.dognation.api.dto.SpotDtos.FrequentBreedsResponse;
 import com.dog.dognation.domain.dog.Dog;
 import com.dog.dognation.domain.dog.DogRepository;
 import jakarta.persistence.EntityNotFoundException;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
+import java.time.DayOfWeek;
 import java.time.OffsetDateTime;
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
@@ -83,6 +87,58 @@ public class SpotService {
         return reviewRepository.findBySpotIdOrderByCreatedAtDesc(spotId);
     }
 
+    private static final ZoneId KST = ZoneId.of("Asia/Seoul");
+
+    /**
+     * 통계용 체크인(PostgreSQL)을 기반으로, 지금과 같은 요일·시간대에 이 스팟에 자주 온
+     * 견종 상위 목록을 반환한다. (방문 횟수 기준, 최근 120일)
+     */
+    @Transactional(readOnly = true)
+    public FrequentBreedsResponse frequentBreeds(Long spotId) {
+        ZonedDateTime now = ZonedDateTime.now(KST);
+        DayOfWeek nowDow = now.getDayOfWeek();
+        int nowBand = timeBand(now.getHour());
+
+        OffsetDateTime since = now.minusDays(120).toOffsetDateTime();
+        List<CheckIn> history = checkInRepository.findBySpotIdAndCheckedInAtAfter(spotId, since);
+
+        // 같은 요일 + 같은 시간대의 체크인만 (방문 1건 = dogId 1개, 중복 허용 → 빈도)
+        List<Long> dogIds = history.stream()
+                .filter(c -> {
+                    ZonedDateTime t = c.getCheckedInAt().atZoneSameInstant(KST);
+                    return t.getDayOfWeek() == nowDow && timeBand(t.getHour()) == nowBand;
+                })
+                .map(CheckIn::getDogId)
+                .toList();
+        if (dogIds.isEmpty()) {
+            return new FrequentBreedsResponse(List.of());
+        }
+
+        Map<Long, String> breedByDog = dogRepository.findAllById(dogIds.stream().distinct().toList()).stream()
+                .filter(d -> d.getBreed() != null && !d.getBreed().isBlank())
+                .collect(Collectors.toMap(Dog::getId, Dog::getBreed));
+
+        Map<String, Long> counts = dogIds.stream()
+                .map(breedByDog::get)
+                .filter(Objects::nonNull)
+                .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
+
+        List<String> top = counts.entrySet().stream()
+                .sorted(Map.Entry.<String, Long>comparingByValue().reversed())
+                .limit(3)
+                .map(Map.Entry::getKey)
+                .toList();
+        return new FrequentBreedsResponse(top);
+    }
+
+    /** 시간대 구간: 0=아침(5-11) 1=낮(11-17) 2=저녁(17-21) 3=밤(그 외). */
+    private int timeBand(int hour) {
+        if (hour >= 5 && hour < 11) return 0;
+        if (hour >= 11 && hour < 17) return 1;
+        if (hour >= 17 && hour < 21) return 2;
+        return 3;
+    }
+
     @Transactional
     public SpotReview addReview(Long spotId, Long userId, String tag, String content) {
         if (!spotRepository.existsById(spotId)) {