first commit. application working

backend/src/main/java/com/weighttracker/service/WeightService.java

@@ -0,0 +1,51 @@
+package com.weighttracker.service;
+
+import com.weighttracker.model.User;
+import com.weighttracker.model.WeightRecord;
+import com.weighttracker.repository.WeightRecordRepository;
+import org.springframework.stereotype.Service;
+
+import java.time.LocalDateTime;
+import java.util.List;
+
+@Service
+public class WeightService {
+    private final WeightRecordRepository repo;
+
+    public WeightService(WeightRecordRepository r) {
+        this.repo = r;
+    }
+
+    public WeightRecord save(WeightRecord w) {
+        return repo.save(w);
+    }
+
+    public List<WeightRecord> last10(User u) {
+        return repo.findTop10ByUserOrderByDateDesc(u);
+    }
+
+    public List<WeightRecord> findByUser(User u) {
+        return repo.findByUserOrderByDateDesc(u);
+    }
+
+    public List<WeightRecord> recordsAfter(User u, LocalDateTime d) {
+        return repo.findByUserAndDateAfterOrderByDateAsc(u, d);
+    }
+
+    public WeightRecord findById(Long id) {
+        return repo.findById(id).orElseThrow();
+    }
+
+    public void deleteById(Long id) {
+        repo.deleteById(id);
+    }
+
+    public List<WeightRecord> recordsBetween(User user, LocalDateTime start, LocalDateTime end) {
+        return repo.findByUserAndDateBetweenOrderByDateAsc(user, start, end);
+    }
+
+    public void deleteByUser(User user) {
+        repo.deleteAllByUser(user);
+    }
+
+}