package com.simpligility.maven.plugins.android.resource;
   
   import org.apache.maven.plugins.shade.relocation.Relocator;
   import org.apache.maven.plugins.shade.resource.ResourceTransformer;
   import org.jdom2.Attribute;
   import org.jdom2.Content;
   import org.jdom2.Document;
   import org.jdom2.Element;
   import org.jdom2.JDOMException;
  import org.jdom2.input.SAXBuilder;
  import org.jdom2.output.Format;
  import org.jdom2.output.XMLOutputter;
  import org.jdom2.xpath.XPath;
  import org.xml.sax.EntityResolver;
  import org.xml.sax.InputSource;
  import org.xml.sax.SAXException;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.StringReader;
  import java.util.Iterator;
  import java.util.List;
  import java.util.jar.JarEntry;
  import java.util.jar.JarOutputStream;
  
  import static java.lang.String.format;
  
  /**
   * Combines multiple occurrences of some XML file
   * by appending contents of specified elements.
   */
  public class XpathAppendingTransformer implements ResourceTransformer
  {
      public static final String XSI_NS = "http://www.w3.org/2001/XMLSchema-instance";
  
      boolean ignoreDtd = true;
  
      String resource;
  
      /** XPATH expression selecting elements */
      String[] elements;
  
      Document doc;
  
      public boolean canTransformResource( String r )
      {
          if ( resource != null && resource.equalsIgnoreCase( r ) )
          {
              return true;
          }
  
          return false;
      }
  
      public void processResource( String resource, InputStream is, List<Relocator> relocators )
              throws IOException
      {
          Document r;
          try
          {
              SAXBuilder builder = new SAXBuilder( false );
              builder.setExpandEntities( false );
              if ( ignoreDtd )
              {
                  builder.setEntityResolver( new EntityResolver()
                  {
                      public InputSource resolveEntity( String publicId, String systemId )
                              throws SAXException, IOException
                      {
                          return new InputSource( new StringReader( "" ) );
                      }
                  } );
              }
              r = builder.build( is );
          }
          catch ( JDOMException e )
          {
              throw new RuntimeException( "Error processing resource " + resource + ": " + e.getMessage(), e );
          }
  
          if ( doc == null )
          {
              doc = r;
          }
          else if ( elements == null || elements.length == 0 )
          {
              appendElement( r.getRootElement(), doc.getRootElement() );
          }
          else
          {
              for ( String xpath : elements )
              {
                  try
                  {
                      XPath path = XPath.newInstance( xpath );
                      Object source = path.selectSingleNode( r.getRootElement() );
                      if ( !( source instanceof Element ) )
                      {
                          throw new IOException( format( "xpath result must be element. %s returned %s",
                                 xpath, source ) );
                     }
                     Object target = path.selectSingleNode( doc.getRootElement() );
                     if ( !( target instanceof Element ) )
                     {
                         throw new IOException( format( "xpath result must be element. %s returned %s",
                                 xpath, target ) );
                     }
                     appendElement( (Element) source, (Element) target );
                 }
                 catch ( JDOMException e )
                 {
                     throw new IOException( e );
                 }
             }
         }
     }
 
     @SuppressWarnings( "unchecked" )
     private void appendElement( Element source, Element target )
     {
         for ( Iterator<Attribute> itr = source.getAttributes().iterator(); itr.hasNext(); )
         {
             Attribute a = itr.next();
             itr.remove();
 
             Attribute mergedAtt = target.getAttribute( a.getName(), a.getNamespace() );
             if ( mergedAtt == null )
             {
                 target.setAttribute( a );
             }
         }
 
         for ( Iterator<Element> itr = source.getChildren().iterator(); itr.hasNext(); )
         {
             Content n = itr.next();
             itr.remove();
 
             target.addContent( n );
         }
     }
 
     public boolean hasTransformedResource()
     {
         return doc != null;
     }
 
     public void modifyOutputStream( JarOutputStream jos )
             throws IOException
     {
         jos.putNextEntry( new JarEntry( resource ) );
 
         new XMLOutputter( Format.getPrettyFormat() ).output( doc, jos );
 
         doc = null;
     }
 }