feat: add stat service

backend/src/main/java/com/openisle/service/StatService.java

@@ -0,0 +1,48 @@
+package com.openisle.service;
+
+import com.openisle.repository.UserRepository;
+import com.openisle.repository.PostRepository;
+import com.openisle.repository.CommentRepository;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Service;
+
+import java.time.LocalDate;
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+@Service
+@RequiredArgsConstructor
+public class StatService {
+    private final UserRepository userRepository;
+    private final PostRepository postRepository;
+    private final CommentRepository commentRepository;
+
+    private Map<LocalDate, Long> toDateMap(LocalDate start, LocalDate end, java.util.List<Object[]> list) {
+        Map<LocalDate, Long> result = new LinkedHashMap<>();
+        for (var obj : list) {
+            LocalDate d = (LocalDate) obj[0];
+            Long c = ((Number) obj[1]).longValue();
+            result.put(d, c);
+        }
+        for (LocalDate d = start; !d.isAfter(end); d = d.plusDays(1)) {
+            result.putIfAbsent(d, 0L);
+        }
+        return result;
+    }
+
+    public Map<LocalDate, Long> countNewUsersRange(LocalDate start, LocalDate end) {
+        java.util.List<Object[]> list = userRepository.countDailyRange(start.atStartOfDay(), end.plusDays(1).atStartOfDay());
+        return toDateMap(start, end, list);
+    }
+
+    public Map<LocalDate, Long> countPostsRange(LocalDate start, LocalDate end) {
+        java.util.List<Object[]> list = postRepository.countDailyRange(start.atStartOfDay(), end.plusDays(1).atStartOfDay());
+        return toDateMap(start, end, list);
+    }
+
+    public Map<LocalDate, Long> countCommentsRange(LocalDate start, LocalDate end) {
+        java.util.List<Object[]> list = commentRepository.countDailyRange(start.atStartOfDay(), end.plusDays(1).atStartOfDay());
+        return toDateMap(start, end, list);
+    }
+}
+