refactor: simplify

Author: metacosm

operator-framework-core/src/main/java/io/javaoperatorsdk/operator/processing/MultiResourceOwner.java

@@ -1,9 +1,25 @@
 package io.javaoperatorsdk.operator.processing.event.source;
 
+import java.util.Optional;
+import java.util.Set;
+
 import io.fabric8.kubernetes.api.model.HasMetadata;
-import io.javaoperatorsdk.operator.processing.MultiResourceOwner;
+import io.javaoperatorsdk.operator.processing.ResourceOwner;
 
 public interface ResourceEventSource<R, P extends HasMetadata> extends EventSource,
-    MultiResourceOwner<R, P> {
+    ResourceOwner<R, P> {
+
+  default Optional<R> getSecondaryResource(P primary) {
+    var resources = getSecondaryResources(primary);
+    if (resources.isEmpty()) {
+      return Optional.empty();
+    } else if (resources.size() == 1) {
+      return Optional.of(resources.iterator().next());
+    } else {
+      throw new IllegalStateException("More than 1 secondary resource related to primary");
+    }
+
+  }
 
+  Set<R> getSecondaryResources(P primary);
 }