added Creating Groups to frontend and saving them in Database. Also prepared some Methods for Snapshot db

src/main/java/mops/gruppen2/service/EventService.java

@@ -0,0 +1,51 @@
+package mops.gruppen2.service;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import mops.gruppen2.domain.EventDTO;
+import mops.gruppen2.domain.event.Event;
+import mops.gruppen2.repository.EventRepository;
+import org.springframework.stereotype.Service;
+
+@Service
+public class EventService {
+    private final SerializationService serializationService;
+    private final EventRepository eventStore;
+
+    public EventService(SerializationService serializationService, EventRepository eventStore) {
+        this.serializationService = serializationService;
+        this.eventStore = eventStore;
+    }
+
+
+    public void saveEvent(Event event){
+        EventDTO eventDTO = getDTO(event);
+        eventStore.save(eventDTO);
+
+    }
+
+    public EventDTO getDTO(Event event){
+        EventDTO eventDTO = new EventDTO();
+        eventDTO.setGroup_id(event.getGroup_id());
+        eventDTO.setUser_id(event.getUser_id());
+        try {
+            eventDTO.setEvent_payload(serializationService.serializeEvent(event));
+        } catch (JsonProcessingException e) {
+            e.printStackTrace();
+        }
+        return  eventDTO;
+    }
+
+    public Long checkGroup() {
+        Long tmpId = 1L;
+        Iterable<EventDTO> eventDTOS = eventStore.findAll();
+        for (EventDTO event : eventDTOS) {
+            if (event.getGroup_id() == null) {
+                return tmpId;
+            }
+            if (tmpId <= event.getGroup_id()) {
+                tmpId++;
+            }
+        }
+        return tmpId;
+    }
+}

src/main/java/mops/gruppen2/service/GroupService.java

@@ -4,6 +4,7 @@ import mops.gruppen2.domain.Group;
 import mops.gruppen2.domain.event.Event;
 import org.springframework.stereotype.Service;
 
+import java.util.ArrayList;
 import java.util.List;
 
 @Service
@@ -15,9 +16,17 @@ public class GroupService {
      * @param eventList Die Events für diese Gruppe
      * @return Gruppe auf aktuellem Stand
      */
-    Group buildGroupFromEvents(List<Event> eventList) {
+    public Group buildGroupFromEvents(List<Event> eventList) {
         Group newGroup = new Group();
         newGroup.apply(eventList);
         return newGroup;
     }
+
+    public Group buildGroupFromEvent(Event event){
+        Group newGroup = new Group();
+        List<Event> eventList = new ArrayList<>();
+        eventList.add(event);
+        newGroup.apply(eventList);
+        return newGroup;
+    }
 }

src/main/java/mops/gruppen2/service/SerializationService.java

@@ -29,16 +29,5 @@ public class SerializationService {
         return json;
     }
 
-    public void saveEvent(Event event){
-        try {
-            EventDTO eventDTO = new EventDTO();
-            eventDTO.setGroup_id(event.getGroup_id());
-            eventDTO.setUser_id(event.getUser_id());
-            eventDTO.setEvent_payload(serializeEvent(event));
-            eventStore.save(eventDTO);
-        } catch (JsonProcessingException e) {
-            e.printStackTrace();
-        }
 
-    }
 }