feat: add a LLMStreamingGenerator class

Convert the langchain4j StreamingResponseHandler to AsyncStream

work on #31

Author: bsorrentino

langchain4j/src/main/java/org/bsc/langgraph4j/langchain4j/generators/LLMStreamingGenerator.java

@@ -0,0 +1,57 @@
+package org.bsc.langgraph4j.langchain4j.generators;
+
+import dev.langchain4j.data.message.AiMessage;
+import dev.langchain4j.model.StreamingResponseHandler;
+import dev.langchain4j.model.output.Response;
+import org.bsc.async.AsyncGenerator;
+import org.bsc.async.AsyncGeneratorQueue;
+
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.LinkedBlockingQueue;
+
+import static java.util.concurrent.CompletableFuture.completedFuture;
+
+public class LLMStreamingGenerator<T> implements AsyncGenerator<String> {
+    private final AsyncGeneratorQueue.Generator<String> generator ;
+
+    public LLMStreamingGenerator( BlockingQueue<AsyncGenerator.Data<String>> queue ) {
+        this.generator = new AsyncGeneratorQueue.Generator<>( queue );
+    }
+
+    public LLMStreamingGenerator() {
+        this( new LinkedBlockingQueue<>());
+    }
+
+    @Override
+    public Data<String> next() {
+        return generator.next();
+    }
+
+    public AsyncGenerator<String> generator( ) {
+        return generator;
+    }
+
+    public StreamingResponseHandler<T> handler() {
+        return new StreamingResponseHandler<T>() {
+
+            @Override
+            public void onNext(String token) {
+                generator.queue().add( AsyncGenerator.Data.of(completedFuture(token)) );
+            }
+
+            @Override
+            public void onComplete(Response<T> response) {
+                generator.queue().add(AsyncGenerator.Data.done());
+            }
+
+            @Override
+            public void onError(Throwable error) {
+                CompletableFuture<String> future = new CompletableFuture<>();
+                future.completeExceptionally(error);
+                generator.queue().add( AsyncGenerator.Data.of(future) );
+            }
+        };
+    }
+
+}