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/*
 * CompositeUnion.java March 2011
 *
 * Copyright (C) 2011, Niall Gallagher 
 *
 * Licensed 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.simpleframework.xml.core;

import org.simpleframework.xml.strategy.Type;
import org.simpleframework.xml.stream.InputNode;
import org.simpleframework.xml.stream.OutputNode;

/**
 * The CompositeUnion object is used to act as a mediator
 * for multiple converters associated with a particular union group.
 * This will basically determine which Converter should be
 * delegated to based on either the XML element name being read or the
 * type of the instance object being written. Selection of the converter
 * is done by consulting the Group of labels representing
 * the union declaration.
 * 
 * @author Niall Gallagher
 */
class CompositeUnion implements Converter {
   
   /**
    * This contains the labels in the union group keyed by name.
    */
   private final LabelMap elements;
   
   /**
    * This is the path expression used to represent this union.
    */
   private final Expression path;
   
   /**
    * This is the current context used for the serialization.
    */
   private final Context context;
   
   /**
    * This contains the group of labels associated with the union.
    */
   private final Group group;
   
   /**
    * This is the type field or method annotated as a union.
    */
   private final Type type;
   
   /**
    * Constructor for the CompositeUnion object. This
    * is used to create a converter that delegates to other associated
    * converters within the union group depending on the XML element
    * name being read or the instance type that is being written.
    * 
    * @param context this is the context used for the serialization
    * @param group this is the union group used for delegation
    * @param path this is the path expression representing this union
    * @param type this is the annotated field or method to be used
    */
   public CompositeUnion(Context context, Group group, Expression path, Type type) throws Exception {
      this.elements = group.getElements();
      this.context = context;
      this.group = group;
      this.type = type;
      this.path = path;
   }

   /**
    * The read method uses the name of the XML element to
    * select a converter to be used to read the instance. Selection of
    * the converter is done by looking up the associated label from
    * the union group using the element name. Once the converter has
    * been selected it is used to read the instance.
    * 
    * @param node this is the XML element used to read the instance
    * 
    * @return this is the instance that has been read by this
    */
   public Object read(InputNode node) throws Exception {
      String name = node.getName();
      String element = path.getElement(name);
      Label label = elements.get(element);
      Converter converter = label.getConverter(context);
      
      return converter.read(node);
   }

   /**
    * The read method uses the name of the XML element to
    * select a converter to be used to read the instance. Selection of
    * the converter is done by looking up the associated label from
    * the union group using the element name. Once the converter has
    * been selected it is used to read the instance.
    * 
    * @param node this is the XML element used to read the instance
    * @param value this is the value that is to be repeated
    * 
    * @return this is the instance that has been read by this
    */
   public Object read(InputNode node, Object value) throws Exception {
      String name = node.getName();
      String element = path.getElement(name);
      Label label = elements.get(element);
      Converter converter = label.getConverter(context);
      
      return converter.read(node, value);
   }
   
   /**
    * The validate method is used to validate the XML
    * element provided using an associated class schema. The schema
    * is selected using the name of the XML element to acquire
    * the associated converter. Once the converter has been acquired
    * it is delegated to and validated against it.
    * 
    * @param node this is the input XML element to be validated
    * 
    * @return this returns true if the node validates 
    */
   public boolean validate(InputNode node) throws Exception {
      String name = node.getName();
      String element = path.getElement(name);
      Label label = elements.get(element);
      Converter converter = label.getConverter(context);
      
      return converter.validate(node);
   }

   /**
    * The write method uses the name of the XML element to
    * select a converter to be used to write the instance. Selection of
    * the converter is done by looking up the associated label from
    * the union group using the instance type. Once the converter has
    * been selected it is used to write the instance.
    * 
    * @param node this is the XML element used to write the instance
    * @param object this is the value that is to be written
    */
   public void write(OutputNode node, Object object) throws Exception {
      Class real = object.getClass();
      Label label = group.getLabel(real);

      if(label == null) {               
         throw new UnionException("Value of %s not declared in %s with annotation %s", real, type, group);
      }
      write(node, object, label);     
   }
   
   /**
    * The write method uses the name of the XML element to
    * select a converter to be used to write the instance. Selection of
    * the converter is done by looking up the associated label from
    * the union group using the instance type. Once the converter has
    * been selected it is used to write the instance.
    * 
    * @param node this is the XML element used to write the instance
    * @param object this is the value that is to be written    
    * @param label this is the label to used to acquire the converter
    */
   private void write(OutputNode node, Object object, Label label) throws Exception {
      label.getConverter(context).write(node, object);
   }

}