refactor: extract ModificationManager for modification creation

Move create/batchCreate transactional logic from ModificationService into
a dedicated ModificationManager. Both ModificationService and WebhookService
delegate to the manager, respecting the Controller -> Service -> Manager
layering rule.

src/main/java/com/onixbyte/deltaforceguide/manager/ModificationManager.java

@@ -0,0 +1,115 @@
+package com.onixbyte.deltaforceguide.manager;
+
+import com.onixbyte.deltaforceguide.domain.entity.Accessory;
+import com.onixbyte.deltaforceguide.domain.entity.Firearm;
+import com.onixbyte.deltaforceguide.domain.entity.Modification;
+import com.onixbyte.deltaforceguide.domain.entity.Tuning;
+import com.onixbyte.deltaforceguide.domain.dto.AccessoryRequest;
+import com.onixbyte.deltaforceguide.domain.dto.ModificationRequest;
+import com.onixbyte.deltaforceguide.domain.dto.ModificationResponse;
+import com.onixbyte.deltaforceguide.domain.dto.TuningRequest;
+import com.onixbyte.deltaforceguide.repository.FirearmRepository;
+import com.onixbyte.deltaforceguide.repository.ModificationRepository;
+import org.springframework.http.HttpStatus;
+import org.springframework.stereotype.Component;
+import org.springframework.transaction.annotation.Transactional;
+import org.springframework.web.server.ResponseStatusException;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Map;
+
+@Component
+public class ModificationManager {
+
+    private final ModificationRepository modificationRepository;
+    private final FirearmRepository firearmRepository;
+
+    public ModificationManager(
+            ModificationRepository modificationRepository,
+            FirearmRepository firearmRepository
+    ) {
+        this.modificationRepository = modificationRepository;
+        this.firearmRepository = firearmRepository;
+    }
+
+    @Transactional
+    public ModificationResponse create(ModificationRequest request) {
+        var firearm = firearmRepository.findById(request.firearmId())
+                .orElseThrow(() -> new ResponseStatusException(HttpStatus.NOT_FOUND,
+                        "Firearm not found: " + request.firearmId()));
+        var modification = toEntity(request, firearm);
+        return ModificationResponse.from(modificationRepository.save(modification));
+    }
+
+    @Transactional
+    public List<ModificationResponse> batchCreate(List<ModificationRequest> requests) {
+        var firearmIds = requests.stream()
+                .map(ModificationRequest::firearmId)
+                .collect(java.util.stream.Collectors.toCollection(LinkedHashSet::new));
+
+        Map<Long, Firearm> firearmMap = new HashMap<>();
+        firearmRepository.findAllById(firearmIds)
+                .forEach(firearm -> firearmMap.put(firearm.getId(), firearm));
+
+        if (firearmMap.size() != firearmIds.size()) {
+            var missing = firearmIds.stream()
+                    .filter((id) -> !firearmMap.containsKey(id))
+                    .toList();
+            throw new ResponseStatusException(HttpStatus.NOT_FOUND,
+                    "Firearm not found: " + missing);
+        }
+
+        var modifications = requests.stream()
+                .map(req -> toEntity(req, firearmMap.get(req.firearmId())))
+                .toList();
+        return modificationRepository.saveAll(modifications)
+                .stream()
+                .map(ModificationResponse::from)
+                .toList();
+    }
+
+    private Modification toEntity(ModificationRequest request, Firearm firearm) {
+        return Modification.builder()
+                .firearm(firearm)
+                .name(request.name())
+                .code(request.code())
+                .tags(request.tags())
+                .accessories(toAccessories(request.accessories()))
+                .note(request.note())
+                .author(request.author())
+                .videoUrl(request.videoUrl())
+                .build();
+    }
+
+    private List<Accessory> toAccessories(List<AccessoryRequest> requests) {
+        if (requests == null) {
+            return new ArrayList<>();
+        }
+        return requests.stream().map(this::toAccessory).toList();
+    }
+
+    private Accessory toAccessory(AccessoryRequest request) {
+        var accessory = new Accessory();
+        accessory.setSlotName(request.slotName());
+        accessory.setAccessoryName(request.accessoryName());
+        accessory.setTunings(toTunings(request.tunings()));
+        return accessory;
+    }
+
+    private List<Tuning> toTunings(List<TuningRequest> requests) {
+        if (requests == null) {
+            return new ArrayList<>();
+        }
+        return requests.stream().map(this::toTuning).toList();
+    }
+
+    private Tuning toTuning(TuningRequest request) {
+        var tuning = new Tuning();
+        tuning.setTuningName(request.tuningName());
+        tuning.setTuningValue(request.tuningValue());
+        return tuning;
+    }
+}

src/main/java/com/onixbyte/deltaforceguide/service/ModificationService.java

@@ -9,6 +9,7 @@ import com.onixbyte.deltaforceguide.domain.entity.Accessory;
 import com.onixbyte.deltaforceguide.domain.entity.Firearm;
 import com.onixbyte.deltaforceguide.domain.entity.Modification;
 import com.onixbyte.deltaforceguide.domain.entity.Tuning;
+import com.onixbyte.deltaforceguide.manager.ModificationManager;
 import com.onixbyte.deltaforceguide.repository.FirearmRepository;
 import com.onixbyte.deltaforceguide.repository.ModificationRepository;
 import com.fasterxml.jackson.core.JsonProcessingException;
@@ -21,10 +22,8 @@ import org.springframework.transaction.annotation.Transactional;
 import org.springframework.web.server.ResponseStatusException;
 
 import java.util.ArrayList;
-import java.util.HashMap;
 import java.util.LinkedHashSet;
 import java.util.List;
-import java.util.Map;
 import java.util.Set;
 
 @Service
@@ -32,15 +31,18 @@ public class ModificationService {
 
     private final ModificationRepository modificationRepository;
     private final FirearmRepository firearmRepository;
+    private final ModificationManager modificationManager;
     private final ObjectMapper objectMapper;
 
     public ModificationService(
             ModificationRepository modificationRepository,
             FirearmRepository firearmRepository,
+            ModificationManager modificationManager,
             ObjectMapper objectMapper
     ) {
         this.modificationRepository = modificationRepository;
         this.firearmRepository = firearmRepository;
+        this.modificationManager = modificationManager;
         this.objectMapper = objectMapper;
     }
 
@@ -79,36 +81,12 @@ public class ModificationService {
 
     @Transactional
     public ModificationResponse create(ModificationRequest request) {
-        Firearm firearm = firearmRepository.findById(request.firearmId())
+        return modificationManager.create(request);
-                .orElseThrow(() -> new ResponseStatusException(HttpStatus.NOT_FOUND, "Firearm not found: " + request.firearmId()));
-
-        Modification modification = toEntity(request, firearm);
-        return ModificationResponse.from(modificationRepository.save(modification));
     }
 
     @Transactional
     public List<ModificationResponse> batchCreate(List<ModificationRequest> requests) {
-        Set<Long> firearmIds = requests.stream()
+        return modificationManager.batchCreate(requests);
-                .map(ModificationRequest::firearmId)
-                .collect(java.util.stream.Collectors.toCollection(LinkedHashSet::new));
-
-        Map<Long, Firearm> firearmMap = new HashMap<>();
-        firearmRepository.findAllById(firearmIds).forEach(firearm -> firearmMap.put(firearm.getId(), firearm));
-
-        if (firearmMap.size() != firearmIds.size()) {
-            List<Long> missingFirearmIds = firearmIds.stream()
-                    .filter(id -> !firearmMap.containsKey(id))
-                    .toList();
-            throw new ResponseStatusException(HttpStatus.NOT_FOUND, "Firearm not found: " + missingFirearmIds);
-        }
-
-        List<Modification> modifications = requests.stream()
-                .map(request -> toEntity(request, firearmMap.get(request.firearmId())))
-                .toList();
-        return modificationRepository.saveAll(modifications)
-                .stream()
-                .map(ModificationResponse::from)
-                .toList();
     }
 
     @Transactional
@@ -155,19 +133,6 @@ public class ModificationService {
         modificationRepository.deleteAllInBatch(modifications);
     }
 
-    private Modification toEntity(ModificationRequest request, Firearm firearm) {
-        return Modification.builder()
-                .firearm(firearm)
-                .name(request.name())
-                .code(request.code())
-                .tags(safeTags(request.tags()))
-                .accessories(toAccessories(request.accessories()))
-                .note(request.note())
-                .author(request.author())
-                .videoUrl(request.videoUrl())
-                .build();
-    }
-
     private List<String> safeTags(List<String> tags) {
         return tags == null ? new ArrayList<>() : tags;
     }