feat: RankingService 클래스 추가 및 랭킹 조회 기능 구현

Author: rnqhstmd

apps/commerce-api/src/main/java/com/loopers/domain/ranking/RankingService.java

@@ -0,0 +1,126 @@
+package com.loopers.domain.ranking;
+
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.data.redis.core.RedisTemplate;
+import org.springframework.data.redis.core.ZSetOperations;
+import org.springframework.stereotype.Service;
+
+import java.time.LocalDate;
+import java.util.*;
+
+/**
+ * 랭킹 조회 서비스 (commerce-api용)
+ */
+@Slf4j
+@Service
+@RequiredArgsConstructor
+public class RankingService {
+
+    private final RedisTemplate<String, String> redisTemplate;
+
+    /**
+     * Top-N 랭킹 조회 (점수 포함)
+     */
+    public List<RankingEntry> getTopNWithScores(LocalDate date, int n) {
+        String key = RankingKey.daily(date);
+
+        try {
+            Set<ZSetOperations.TypedTuple<String>> tuples = redisTemplate.opsForZSet()
+                    .reverseRangeWithScores(key, 0, n - 1);
+
+            if (tuples == null || tuples.isEmpty()) {
+                return Collections.emptyList();
+            }
+
+            return convertToRankingEntries(tuples);
+        } catch (Exception e) {
+            log.error("Top-N 랭킹 조회 실패: key={}, n={}", key, n, e);
+            return Collections.emptyList();
+        }
+    }
+
+    /**
+     * 페이지네이션 랭킹 조회
+     */
+    public List<RankingEntry> getRankingPage(LocalDate date, int page, int size) {
+        String key = RankingKey.daily(date);
+        long start = (long) page * size;
+        long end = start + size - 1;
+
+        try {
+            Set<ZSetOperations.TypedTuple<String>> tuples = redisTemplate.opsForZSet()
+                    .reverseRangeWithScores(key, start, end);
+
+            if (tuples == null || tuples.isEmpty()) {
+                return Collections.emptyList();
+            }
+
+            return convertToRankingEntries(tuples);
+        } catch (Exception e) {
+            log.error("랭킹 페이지 조회 실패: key={}, page={}, size={}", key, page, size, e);
+            return Collections.emptyList();
+        }
+    }
+
+    /**
+     * 특정 상품의 순위 조회
+     *
+     * @return 순위 (1부터 시작), 랭킹에 없으면 null
+     */
+    public Long getRank(Long productId, LocalDate date) {
+        String key = RankingKey.daily(date);
+        String member = productId.toString();
+
+        try {
+            Long rank = redisTemplate.opsForZSet().reverseRank(key, member);
+            return rank != null ? rank + 1 : null;
+        } catch (Exception e) {
+            log.error("순위 조회 실패: key={}, productId={}", key, productId, e);
+            return null;
+        }
+    }
+
+    /**
+     * 특정 상품의 점수 조회
+     */
+    public Double getScore(Long productId, LocalDate date) {
+        String key = RankingKey.daily(date);
+        String member = productId.toString();
+
+        try {
+            return redisTemplate.opsForZSet().score(key, member);
+        } catch (Exception e) {
+            log.error("점수 조회 실패: key={}, productId={}", key, productId, e);
+            return null;
+        }
+    }
+
+    /**
+     * 랭킹에 진입한 상품 수 조회
+     */
+    public Long getRankingSize(LocalDate date) {
+        String key = RankingKey.daily(date);
+
+        try {
+            Long size = redisTemplate.opsForZSet().zCard(key);
+            return size != null ? size : 0L;
+        } catch (Exception e) {
+            log.error("랭킹 사이즈 조회 실패: key={}", key, e);
+            return 0L;
+        }
+    }
+
+    private List<RankingEntry> convertToRankingEntries(Set<ZSetOperations.TypedTuple<String>> tuples) {
+        List<RankingEntry> entries = new ArrayList<>();
+        for (ZSetOperations.TypedTuple<String> tuple : tuples) {
+            if (tuple.getValue() != null && tuple.getScore() != null) {
+                entries.add(new RankingEntry(
+                        Long.parseLong(tuple.getValue()),
+                        tuple.getScore()
+                ));
+            }
+        }
+        return entries;
+    }
+}