Issue #559: Extended SignalInformationPoint.

It is now possible check whether a Signal provides an EntityId and to optionally obtain the EntityId from a Signal.

Signed-off-by: Juergen Fickel <juergen.fickel@bosch.io>

internal/models/signal/src/main/java/org/eclipse/ditto/internal/models/signal/SignalInformationPoint.java

@@ -12,9 +12,13 @@
  */
 package org.eclipse.ditto.internal.models.signal;
 
+import java.util.Optional;
+
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
 
+import org.eclipse.ditto.base.model.entity.id.EntityId;
+import org.eclipse.ditto.base.model.entity.id.WithEntityId;
 import org.eclipse.ditto.base.model.headers.WithDittoHeaders;
 import org.eclipse.ditto.base.model.signals.Signal;
 import org.eclipse.ditto.base.model.signals.WithType;
@@ -129,4 +133,38 @@ public static boolean isChannelLive(@Nullable final WithDittoHeaders signal) {
         return result;
     }
 
+    /**
+     * Indicates whether the specified signal argument provides an entity ID.
+     *
+     * @param signal the signal to be checked.
+     * @return {@code true} if {@code signal} provides an entity ID because it implements {@link WithEntityId}.
+     * {@code false} else.
+     */
+    public static boolean isWithEntityId(@Nullable final Signal<?> signal) {
+        final boolean result;
+        if (null != signal) {
+            result = WithEntityId.class.isAssignableFrom(signal.getClass());
+        } else {
+            result = false;
+        }
+        return result;
+    }
+
+    /**
+     * Returns the {@link EntityId} for the specified signal argument.
+     *
+     * @param signal the signal to get the entity ID from.
+     * @return an {@code Optional} containing the signal's entity ID if it provides one, an empty {@code Optional} else.
+     * @see #isWithEntityId(Signal)
+     */
+    public static Optional<EntityId> getEntityId(@Nullable final Signal<?> signal) {
+        final Optional<EntityId> result;
+        if (isWithEntityId(signal)) {
+            result = Optional.of(((WithEntityId) signal).getEntityId());
+        } else {
+            result = Optional.empty();
+        }
+        return result;
+    }
+
 }

internal/models/signal/src/test/java/org/eclipse/ditto/internal/models/signal/SignalInformationPointTest.java

@@ -24,8 +24,11 @@
 import org.eclipse.ditto.internal.models.signal.common.SignalInterfaceImplementations;
 import org.eclipse.ditto.messages.model.signals.commands.MessageCommand;
 import org.eclipse.ditto.messages.model.signals.commands.MessageCommandResponse;
+import org.eclipse.ditto.things.model.ThingId;
 import org.eclipse.ditto.things.model.signals.commands.ThingCommand;
 import org.eclipse.ditto.things.model.signals.commands.ThingCommandResponse;
+import org.eclipse.ditto.things.model.signals.commands.query.RetrieveThing;
+import org.eclipse.ditto.things.model.signals.commands.query.RetrieveThings;
 import org.junit.Before;
 import org.junit.BeforeClass;
 import org.junit.Rule;
@@ -253,6 +256,44 @@ public void isChannelLiveForSignalWithoutChannelHeaderReturnsTrue() {
         assertThat(SignalInformationPoint.isChannelLive(signalMock)).isFalse();
     }
 
+    @Test
+    public void isWithEntityIdForNullSignalReturnsFalse() {
+        assertThat(SignalInformationPoint.isWithEntityId(null)).isFalse();
+    }
+
+    @Test
+    public void isWithEntityIdForSignalImplementingWithEntityIdReturnsTrue() {
+        final var signal = RetrieveThing.of(ThingId.generateRandom(), dittoHeaders);
+
+        assertThat(SignalInformationPoint.isWithEntityId(signal)).isTrue();
+    }
+
+    @Test
+    public void isWithEntityIdForSignalNotImplementingWithEntityIdReturnsFalse() {
+        final var signal = RetrieveThings.getBuilder(ThingId.generateRandom()).dittoHeaders(dittoHeaders).build();
+
+        assertThat(SignalInformationPoint.isWithEntityId(signal)).isFalse();
+    }
+
+    @Test
+    public void getEntityIdForNullSignalReturnsEmptyOptional() {
+        assertThat(SignalInformationPoint.getEntityId(null)).isEmpty();
+    }
+
+    @Test
+    public void getEntityIdForSignalWithEntityIdReturnsOptionalWithEntityId() {
+        final var signal = RetrieveThing.of(ThingId.generateRandom(), dittoHeaders);
+
+        assertThat(SignalInformationPoint.getEntityId(signal)).hasValue(signal.getEntityId());
+    }
+
+    @Test
+    public void getEntityIdForSignalWithoutEntityIdReturnsEmptyOptional() {
+        final var signal = RetrieveThings.getBuilder(ThingId.generateRandom()).dittoHeaders(dittoHeaders).build();
+
+        assertThat(SignalInformationPoint.getEntityId(signal)).isEmpty();
+    }
+
     private static String getSimpleClassName(final Object o) {
         final var oClass = o.getClass();
         return oClass.getSimpleName();