src/main/java/org/apache/commons/scxml2/model/PayloadBuilder.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.scxml2.model;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.StringTokenizer;

import org.apache.commons.scxml2.Context;
import org.apache.commons.scxml2.ErrorReporter;
import org.apache.commons.scxml2.Evaluator;
import org.apache.commons.scxml2.SCXMLExpressionException;
import org.apache.commons.scxml2.semantics.ErrorConstants;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

/**
 * Utility class to build payload from {@link Param}s and/or a namelist
 */
public class PayloadBuilder {

    /**
     * Payload data values wrapper list needed when multiple variable entries use the same names.
     * The multiple values are then wrapped in a list. The PayloadBuilder uses this 'marker' list
     * to distinguish between entry values which are a list themselves and the wrapper list.
     */
    private static class DataValueList extends ArrayList {
    }

    /**
     * Adds an attribute and value to a payload data map.
     * <p>
     * As the SCXML specification allows for multiple payload attributes with the same name, this
     * method takes care of merging multiple values for the same attribute in a list of values.
     * </p>
     * <p>
     * Furthermore, as modifications of payload data on either the sender or receiver side should affect the
     * the other side, attribute values (notably: {@link Node} value only for now) is cloned first before being added
     * to the payload data map. This includes 'nested' values within a {@link NodeList}, {@link List} or {@link Map}.
     * </p>
     * @param attrName the name of the attribute to add
     * @param attrValue the value of the attribute to add
     * @param payload the payload data map to be updated
     */
    @SuppressWarnings("unchecked")
    public static void addToPayload(final String attrName, final Object attrValue, final Map<String, Object> payload) {
        DataValueList valueList = null;
        Object value = payload.get(attrName);
        if (value != null) {
            if (value instanceof DataValueList) {
                valueList = (DataValueList)value;
            }
            else {
                valueList = new DataValueList();
                valueList.add(value);
                payload.put(attrName, valueList);
            }
        }
        value = attrValue;
        if (value instanceof List) {
            if (valueList == null) {
                valueList = new DataValueList();
                payload.put(attrName, valueList);
            }
            valueList.addAll((List)value);
        }
        else if (valueList != null) {
            valueList.add(value);
        }
        else {
            payload.put(attrName, value);
        }
    }

    /**
     * Adds data to the payload data map based on the {@link Param}s of this {@link ParamsContainer}
     * @param ctx The Context to look up the data
     * @param evaluator the evaluator to evaluate/lookup the data
     * @param paramsList the list of params
     * @param payload the payload data map to be updated
     * @throws SCXMLExpressionException if a malformed or invalid expression is evaluated
     * @see PayloadBuilder#addToPayload(String, Object, java.util.Map)
     */
    public static void addParamsToPayload(final Context ctx, final Evaluator evaluator, final List<Param> paramsList,
                                          final Map<String, Object> payload)
            throws SCXMLExpressionException {
        if (!paramsList.isEmpty()) {
            Object paramValue;
            for (final Param p : paramsList) {
                if (p.getExpr() != null) {
                    paramValue = evaluator.eval(ctx, p.getExpr());
                }
                else if (p.getLocation() != null) {
                    paramValue = evaluator.eval(ctx, p.getLocation());
                }
                else {
                    // ignore invalid param definition
                    continue;
                }
                addToPayload(p.getName(), evaluator.cloneData(paramValue), payload);
            }
        }
    }

    /**
     * Adds data to the payload data map based on the namelist which names are location expressions
     * (typically data ids or for example XPath variables). The names and the values they 'point' at
     * are added to the payload data map.
     * @param parentState the enterable state in which the namelist holder is defined
     * @param ctx the Context to look up the data
     * @param evaluator the evaluator to evaluate/lookup the data
     * @param errorReporter to report errors
     * @param namelist the namelist
     * @param payload the payload data map to be updated
     * @throws SCXMLExpressionException if a malformed or invalid expression is evaluated
     * @see PayloadBuilder#addToPayload(String, Object, java.util.Map)
     */
    public static void addNamelistDataToPayload(final EnterableState parentState, final Context ctx,
                                                final Evaluator evaluator, final ErrorReporter errorReporter,
                                                final String namelist, final Map<String, Object> payload)
            throws SCXMLExpressionException {
        if (namelist != null) {
            final StringTokenizer tkn = new StringTokenizer(namelist);
            while (tkn.hasMoreTokens()) {
                final String varName = tkn.nextToken();
                final Object varObj = evaluator.eval(ctx, varName);
                if (varObj == null) {
                    //considered as a warning here
                    errorReporter.onError(ErrorConstants.UNDEFINED_VARIABLE, varName + " = null", parentState);
                }
                addToPayload(varName, evaluator.cloneData(varObj), payload);
            }
        }
    }
}