feat: adds subgraph node action

work on #39

Author: bsorrentino

core-jdk8/src/main/java/org/bsc/langgraph4j/subgraph/SubgraphNodeAction.java

@@ -0,0 +1,35 @@
+package org.bsc.langgraph4j.subgraph;
+
+import lombok.NonNull;
+import org.bsc.async.AsyncGenerator;
+import org.bsc.langgraph4j.CompiledGraph;
+import org.bsc.langgraph4j.NodeOutput;
+import org.bsc.langgraph4j.RunnableConfig;
+import org.bsc.langgraph4j.action.AsyncNodeActionWithConfig;
+import org.bsc.langgraph4j.action.NodeActionWithConfig;
+import org.bsc.langgraph4j.state.AgentState;
+
+import java.util.Map;
+
+import static org.bsc.langgraph4j.utils.CollectionsUtils.mapOf;
+
+public class SubgraphNodeAction<State extends AgentState> implements NodeActionWithConfig<State> {
+
+    public static <State extends AgentState> AsyncNodeActionWithConfig<State> of( @NonNull  CompiledGraph<State> subGraph ) {
+        return AsyncNodeActionWithConfig.node_async( new SubgraphNodeAction<State>(subGraph) );
+    }
+
+    final CompiledGraph<State> subGraph;
+
+    protected SubgraphNodeAction(CompiledGraph<State> subGraph ) {
+        this.subGraph = subGraph;
+    }
+
+    @Override
+    public Map<String, Object> apply(State state, RunnableConfig config) throws Exception {
+
+        AsyncGenerator<NodeOutput<State>> generator = subGraph.stream( state.data(), config );
+
+        return mapOf( "_subgraph", generator );
+    }
+}