begin StationService implementation

src/main/java/de/pnreichmuth/timekeep_backend/entities/Station.java

@@ -48,4 +48,10 @@ public class Station {
         passedTeams.remove(team);
         passingTimes.remove(team);
     }
+
+    public String setPasswordHash(String passwordHash){
+        if(this.passwordHash != null) throw new IllegalStateException("Password has already been set");
+        this.passwordHash = passwordHash;
+        return this.passwordHash;
+    }
 }

src/main/java/de/pnreichmuth/timekeep_backend/services/StationService.java

@@ -1,16 +1,42 @@
 package de.pnreichmuth.timekeep_backend.services;
 
 import de.pnreichmuth.timekeep_backend.entities.Station;
+import de.pnreichmuth.timekeep_backend.exceptions.StationExistsException;
 import de.pnreichmuth.timekeep_backend.repositories.StationRepository;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.stereotype.Service;
 
+import java.util.List;
 import java.util.Optional;
+import java.util.UUID;
 
 @Service
 @Slf4j
 @RequiredArgsConstructor
 public class StationService {
+    private final StationRepository stationRepository;
+
+    private void checkIfStationIsDuplicate(Station station){
+        List<Station> stations = stationRepository.findAll();
+        if(stations.isEmpty()) return;
+        if(
+                stations.stream().anyMatch(
+                        dbStation -> dbStation.getName().equals(station.getName())
+                                && dbStation.getLocation().equals(station.getLocation())
+                        && !dbStation.getId().equals(station.getId())
+                )
+        ) throw new StationExistsException(
+                "A station named %s already exists at the location %s".formatted(station.getName(), station.getLocation()),
+                station
+        );
+    }
+
+    public Optional<Station> createStation(String name, String location){
+        Station station = new Station(name,location);
+        checkIfStationIsDuplicate(station);
+        stationRepository.save(station);
+        return Optional.of(station);
+    }
 
 }