Fix drawn players

src/main/java/nl/connectedit/swiss/domain/entity/Tournament.java

@@ -1,6 +1,7 @@
 package nl.connectedit.swiss.domain.entity;
 
 import jakarta.persistence.*;
+import java.util.HashSet;
 import lombok.Getter;
 import lombok.Setter;
 import nl.connectedit.swiss.domain.EventType;
@@ -68,4 +69,23 @@ public class Tournament extends AbstractEntity {
             .collect(Collectors.toCollection(ArrayList::new));
     }
 
+    public boolean hasPlayersDrawnOutMaxOnce() {
+        var drawnOutPlayers = new HashSet<Player>();
+        for (var event : events) {
+            for (var group : event.getGroups()) {
+                for (var round : group.getRounds()) {
+                    var drawnOut = round.getDrawnOut();
+                    if (drawnOut != null) {
+                        if (!drawnOutPlayers.add(drawnOut.getPlayer1())) {
+                            return false;
+                        }
+                        if (drawnOut.getPlayer2() != null && !drawnOutPlayers.add(drawnOut.getPlayer2())) {
+                            return false;
+                        }
+                    }
+                }
+            }
+        }
+        return true;
+    }
 }