/*

  * CompositeValue.java July 2007

  *

  * Copyright (C) 2007, Niall Gallagher <niallg@users.sf.net>

  *

  * This library is free software; you can redistribute it and/or

  * modify it under the terms of the GNU Lesser General Public

  * License as published by the Free Software Foundation.

  *

  * This library is distributed in the hope that it will be useful,

  * but WITHOUT ANY WARRANTY; without even the implied warranty of

  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 

  * GNU Lesser General Public License for more details.

  *

  * You should have received a copy of the GNU Lesser General 

  * Public License along with this library; if not, write to the 

  * Free Software Foundation, Inc., 59 Temple Place, Suite 330, 

  * Boston, MA  02111-1307  USA

  */

 package org.simpleframework.xml.load;

 import org.simpleframework.xml.stream.InputNode;

 import org.simpleframework.xml.stream.OutputNode;

 /**

  * The <code>CompositeValue</code> object is used to convert an object

  * to an from an XML element. This accepts only composite objects and

  * will maintain all references within the object using the cycle

  * strategy if required. This also ensures that should the value to

  * be written to the XML element be null that nothing is written. 

  * 

  * @author Niall Gallagher

  * 

  * @see org.simpleframework.xml.ElementMap

  */

 class CompositeValue implements Converter {

    /**

     * This is the traverser used to read and write the value with.

     */

    private final Traverser root;

    /**

     * This is the entry object used to provide configuration details.

     */   

    private final Entry entry;

    /**

     * This represents the type of object the value is written as.

     */

    private final Class type;

    /**

     * Constructor for the <code>CompositeValue</code> object. This 

     * will create an object capable of reading an writing composite 

     * values from an XML element. This also allows a parent element 

     * to be created to wrap the key object if desired.

     * 

     * @param root this is the root context for the serialization

     * @param entry this is the entry object used for configuration

     * @param type this is the type of object the value represents

     */

    public CompositeValue(Source root, Entry entry, Class type) throws Exception {

       this.root = new Traverser(root);

       this.entry = entry;

       this.type = type;

    }

    /**

     * This method is used to read the value object from the node. The 

     * value read from the node is resolved using the template filter.

     * If the value data can not be found according to the annotation 

     * attributes then null is assumed and returned.

     * 

     * @param node this is the node to read the value object from

     * 

     * @return this returns the value deserialized from the node

     */ 

    public Object read(InputNode node) throws Exception { 

       InputNode next = node.getNext();

       if(next == null) {

          return null;

       }

       if(next.isEmpty()) {

          return null;

       }

       return root.read(next, type);

    }

    /**

     * This method is used to read the value object from the node. The 

     * value read from the node is resolved using the template filter.

     * If the value data can not be found according to the annotation 

     * attributes then null is assumed and the node is valid.

     * 

     * @param node this is the node to read the value object from

     * 

     * @return this returns true if this represents a valid value

     */ 

    public boolean validate(InputNode node) throws Exception { 

       String name = entry.getValue();

       if(name == null) {

          name = Factory.getName(type);

       }

       return validate(node, name);

    }  

    /**

     * This method is used to read the value object from the node. The 

     * value read from the node is resolved using the template filter.

     * If the value data can not be found according to the annotation 

     * attributes then null is assumed and the node is valid.

     * 

     * @param node this is the node to read the value object from

     * @param name this is the name of the value element

     * 

     * @return this returns true if this represents a valid value

     */    

    private boolean validate(InputNode node, String name) throws Exception {      

       InputNode next = node.getNext(name);

       if(next == null) {

          return true;

       }

       if(next.isEmpty()) {

          return true;

       }

       return root.validate(next, type);

    }

    /**

     * This method is used to write the value to the specified node.

     * The value written to the node must be a composite object and if

     * the object provided to this is null then nothing is written.

     * 

     * @param node this is the node that the value is written to

     * @param item this is the item that is to be written

     */

    public void write(OutputNode node, Object item) throws Exception {

       String name = entry.getValue();

       if(name == null) {

          name = Factory.getName(type);

       }

       root.write(node, item, type, name);      

    }

 }