code: package org.eclipse.milo.opcua.sdk.client.model.types.variables;
  
  import java.util.concurrent.CompletableFuture;
  
  import org.eclipse.milo.opcua.sdk.core.QualifiedProperty;
  import org.eclipse.milo.opcua.sdk.core.ValueRanks;
  import org.eclipse.milo.opcua.stack.core.UaException;
  import org.eclipse.milo.opcua.stack.core.types.builtin.DateTime;
  import org.eclipse.milo.opcua.stack.core.types.builtin.ExpandedNodeId;
  import org.eclipse.milo.opcua.stack.core.types.builtin.StatusCode;
  
  public interface ConditionVariableType extends BaseDataVariableType {
      QualifiedProperty<DateTime> SOURCE_TIMESTAMP = new QualifiedProperty<>(
          "http://opcfoundation.org/UA/",
          "SourceTimestamp",
          ExpandedNodeId.parse("nsu=http://opcfoundation.org/UA/;i=294"),
          ValueRanks.Scalar,
          DateTime.class
      );
  
      /**
       * Get the local value of the SourceTimestamp Node.
       * <p>
       * The returned value is the last seen; it is not read live from the server.
       *
       * @return the local value of the SourceTimestamp Node.
       * @throws UaException if an error occurs creating or getting the SourceTimestamp Node.
       */
      DateTime getSourceTimestamp() throws UaException;
  
      /**
       * Set the local value of the SourceTimestamp Node.
       * <p>
       * The value is only updated locally; it is not written to the server.
       *
       * @param sourceTimestamp the local value to set for the SourceTimestamp Node.
       * @throws UaException if an error occurs creating or getting the SourceTimestamp Node.
       */
      void setSourceTimestamp(DateTime sourceTimestamp) throws UaException;
  
      /**
       * Read the value of the SourceTimestamp Node from the server and update the local value if the
       * operation succeeds.
       *
       * @return the {@link DateTime} value read from the server.
       * @throws UaException if a service- or operation-level error occurs.
       */
      DateTime readSourceTimestamp() throws UaException;
  
      /**
       * Write a new value for the SourceTimestamp Node to the server and update the local value if
       * the operation succeeds.
       *
       * @param sourceTimestamp the {@link DateTime} value to write to the server.
       * @throws UaException if a service- or operation-level error occurs.
       */
      void writeSourceTimestamp(DateTime sourceTimestamp) throws UaException;
  
      /**
       * An asynchronous implementation of {@link #readSourceTimestamp()}.
       *
       * @return a CompletableFuture that completes successfully with the property value or completes
       * exceptionally if an operation- or service-level error occurs.
       */
      CompletableFuture<? extends DateTime> readSourceTimestampAsync();
  
      /**
       * An asynchronous implementation of {@link #writeSourceTimestamp(DateTime)}.
       *
       * @return a CompletableFuture that completes successfully with the operation result or
       * completes exceptionally if a service-level error occurs.
       */
      CompletableFuture<StatusCode> writeSourceTimestampAsync(DateTime sourceTimestamp);
  
      /**
       * Get the SourceTimestamp {@link PropertyType} Node, or {@code null} if it does not exist.
       * <p>
       * The Node is created when first accessed and cached for subsequent calls.
       *
       * @return the SourceTimestamp {@link PropertyType} Node, or {@code null} if it does not exist.
       * @throws UaException if an error occurs creating or getting the Node.
       */
      PropertyType getSourceTimestampNode() throws UaException;
  
      /**
       * Asynchronous implementation of {@link #getSourceTimestampNode()}.
       *
       * @return a CompletableFuture that completes successfully with the
       * ? extends PropertyType Node or completes exceptionally if an error occurs
       * creating or getting the Node.
       */
      CompletableFuture<? extends PropertyType> getSourceTimestampNodeAsync();
  }
  