Fix area boundary auto-removal with merged and detached Networks

iidm/iidm-impl/src/main/java/com/powsybl/iidm/network/impl/AreaImpl.java

@@ -48,9 +48,19 @@ public void beforeRemoval(Identifiable<?> identifiable) {
         }
     }
 
+    /**
+     * Must be called whenever the Area is moved to a different root Network when merging and detaching.
+     * @param fromNetwork previous root network
+     * @param toNetwork new root network
+     */
+    void moveListener(NetworkImpl fromNetwork, NetworkImpl toNetwork) {
+        fromNetwork.removeListener(this.areaListener);
+        toNetwork.addListener(this.areaListener);
+    }
+
     private final NetworkListener areaListener;
 
-    public AreaImpl(Ref<NetworkImpl> ref, Ref<SubnetworkImpl> subnetworkRef, String id, String name, boolean fictitious, String areaType,
+    AreaImpl(Ref<NetworkImpl> ref, Ref<SubnetworkImpl> subnetworkRef, String id, String name, boolean fictitious, String areaType,
                     double acInterchangeTarget) {
         super(id, name, fictitious);
         this.networkRef = Objects.requireNonNull(ref);

iidm/iidm-impl/src/main/java/com/powsybl/iidm/network/impl/NetworkImpl.java

@@ -1018,6 +1018,11 @@ private void merge(Network other) {
 
         checkMergeability(otherNetwork);
 
+        otherNetwork.getAreaStream().forEach(a -> {
+            AreaImpl area = (AreaImpl) a;
+            area.moveListener(otherNetwork, this);
+        });
+
         // try to find dangling lines couples
         List<DanglingLinePair> lines = new ArrayList<>();
         Map<String, List<DanglingLine>> dl1byPairingKey = new HashMap<>();

iidm/iidm-impl/src/main/java/com/powsybl/iidm/network/impl/SubnetworkImpl.java

@@ -805,7 +805,7 @@ public Network detach() {
         transferExtensions(this, detachedNetwork);
         transferProperties(this, detachedNetwork);
 
-        // Memorize the network identifiables/voltageAngleLimits before moving references (to use them latter)
+        // Memorize the network identifiables/voltageAngleLimits before moving references (to use them later)
         Collection<Identifiable<?>> identifiables = getIdentifiables();
         Iterable<VoltageAngleLimit> vals = getVoltageAngleLimits();
 
@@ -831,6 +831,11 @@ public Network detach() {
             detachedNetwork.getVoltageAngleLimitsIndex().put(val.getId(), val);
         }
 
+        detachedNetwork.getAreaStream().forEach(a -> {
+            AreaImpl area = (AreaImpl) a;
+            area.moveListener(previousRootNetwork, detachedNetwork);
+        });
+
         // We don't control that regulating terminals and phase/ratio regulation terminals are in the same subnetwork
         // as their network elements (generators, PSTs, ...). It is unlikely that those terminals and their elements
         // are in different subnetworks but nothing prevents it. For now, we ignore this case, but it may be necessary

iidm/iidm-tck/src/test/java/com/powsybl/iidm/network/tck/AbstractAreaTest.java

@@ -11,6 +11,7 @@
 import com.powsybl.commons.PowsyblException;
 import com.powsybl.iidm.network.*;
 import com.powsybl.iidm.network.test.EurostagTutorialExample1Factory;
+import com.powsybl.iidm.network.test.FourSubstationsNodeBreakerFactory;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.mockito.Mockito;
@@ -424,6 +425,41 @@ public void removeEquipmentRemovesAreaBoundary() {
         assertEquals(2, controlAreaB.getAreaBoundaryStream().count());
     }
 
+    @Test
+    public void removeEquipmentRemovesAreaBoundaryMergeAndDetach() {
+        // do a merge
+        Network fourBus = FourSubstationsNodeBreakerFactory.create();
+        Network merged = Network.merge(network, fourBus);
+        network = merged.getSubnetwork("sim1");
+        controlAreaA = network.getArea("ControlArea_A");
+        controlAreaB = network.getArea("ControlArea_B");
+        dlXnode1A = network.getDanglingLine("NHV1_XNODE1");
+        tieLine1 = network.getTieLine("NHV1_NHV2_1");
+        assertEquals(2, controlAreaA.getAreaBoundaryStream().count());
+        assertEquals(2, controlAreaB.getAreaBoundaryStream().count());
+
+        // Verify the cleanup listener is now effective on the merged network
+        tieLine1.remove();
+        dlXnode1A.remove();
+
+        assertEquals(1, controlAreaA.getAreaBoundaryStream().count());
+        assertEquals(2, controlAreaB.getAreaBoundaryStream().count());
+
+        // now detach
+        network = network.detach();
+        controlAreaA = network.getArea("ControlArea_A");
+        controlAreaB = network.getArea("ControlArea_B");
+        dlXnode2A = network.getDanglingLine("NVH1_XNODE2");
+        tieLine2 = network.getTieLine("NHV1_NHV2_2");
+
+        // Verify the cleanup listener is now effective on the detached network
+        tieLine2.remove();
+        dlXnode2A.remove();
+
+        assertEquals(0, controlAreaA.getAreaBoundaryStream().count());
+        assertEquals(2, controlAreaB.getAreaBoundaryStream().count());
+    }
+
     @Test
     public void throwBoundaryOtherNetwork() {
         Network subnetwork = network.createSubnetwork("subnetwork_id", "Subnetwork", "json");