feat(Checkpoint): store the nextNodeId

work on #14

core-jdk8/src/main/java/org/bsc/langgraph4j/checkpoint/Checkpoint.java

@@ -1,15 +1,12 @@
 package org.bsc.langgraph4j.checkpoint;
 
-import lombok.Data;
+import lombok.*;
 import org.bsc.langgraph4j.state.AgentState;
+import org.bsc.langgraph4j.state.Channel;
 
 import java.io.Externalizable;
-import java.io.IOException;
-import java.io.ObjectInput;
-import java.io.ObjectOutput;
 import java.util.*;
 
-
 /**
  * Represents a checkpoint of an agent state.
  *
@@ -21,32 +18,65 @@
  * @see AgentState
  * @see Externalizable
  */
+@Getter
+@ToString
 public class Checkpoint {
 
-    @lombok.Value(staticConstructor="of")
-    public static class Value {
-        AgentState state;
-        String nodeId;
-    }
+    private String id = UUID.randomUUID().toString();
+    private AgentState state = null;
+    private String nodeId = null ;
+    private String nextNodeId = null;
 
-    String id;
-    Value value;
+    private Checkpoint() {
+    }
 
-    public final String getId() {
-        return id;
+    private Checkpoint( Checkpoint checkpoint ) {
+        this.id = checkpoint.id;
+        this.state = checkpoint.state;
+        this.nodeId = checkpoint.nodeId;
+        this.nextNodeId = checkpoint.nextNodeId;
     }
-    public final Value getValue() {
-        return value;
+
+    public static Builder builder() {
+        return new Builder();
     }
 
-    public Checkpoint( Value value ) {
-        this(UUID.randomUUID().toString(), value );
+    public static class Builder {
+        private final Checkpoint result = new Checkpoint();;
+
+        public Builder id( String id ) {
+            result.id = id;
+            return this;
+        }
+        public Builder state( AgentState state ) {
+            result.state = state;
+            return this;
+        }
+        public Builder nodeId( String nodeId ) {
+            result.nodeId = nodeId;
+            return this;
+        }
+        public Builder nextNodeId( String nextNodeId ) {
+            result.nextNodeId = nextNodeId;
+            return this;
+        }
+
+        public Checkpoint build() {
+            Objects.requireNonNull( result.id, "Checkpoint.id cannot be null" );
+            Objects.requireNonNull( result.state, "Checkpoint.state cannot be null" );
+            Objects.requireNonNull( result.nodeId, "Checkpoint.nodeId cannot be null" );
+            Objects.requireNonNull( result.nextNodeId, "Checkpoint.nextNodeId cannot be null" );
+
+            return result;
+
+        }
     }
-    public Checkpoint(String id, Value value) {
-        Objects.requireNonNull(id, "id cannot be null");
-        Objects.requireNonNull(value, "value cannot be null");
-        this.id = id;
-        this.value = value;
+    public Checkpoint updateState(Map<String,Object> values, Map<String, Channel<?>> channels ) {
+
+        Checkpoint result = new Checkpoint( this );
+        Map<String,Object> data = AgentState.updateState( state, values, channels );
+        result.state = new AgentState(data);
+        return result;
     }
 
 }