package org.apache.maven.project;
   
   /*
    * 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.
   */
  
  import java.io.BufferedInputStream;
  import java.io.File;
  import java.io.FileInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.jar.JarFile;
  import java.util.zip.ZipEntry;
  
  import org.codehaus.plexus.util.IOUtil;
  import org.codehaus.plexus.util.ReaderFactory;
  import org.codehaus.plexus.util.xml.Xpp3Dom;
  import org.codehaus.plexus.util.xml.Xpp3DomBuilder;
  import org.codehaus.plexus.util.xml.pull.XmlPullParserException;
  
  /**
   * Creates an extension descriptor from some XML stream.
   *
   * @author Benjamin Bentmann
   */
  public class ExtensionDescriptorBuilder
  {
  
      /**
       * @since 3.3.0 
       */
      public String getExtensionDescriptorLocation()
      {
          return "META-INF/maven/extension.xml";
      }
  
      /**
       * Extracts the extension descriptor (if any) from the specified JAR file.
       *
       * @param extensionJar The JAR file or directory to extract the descriptor from, must not be {@code null}.
       * @return The extracted descriptor or {@code null} if no descriptor was found.
       * @throws IOException If the descriptor is present but could not be parsed.
       */
      public ExtensionDescriptor build( File extensionJar )
          throws IOException
      {
          ExtensionDescriptor extensionDescriptor = null;
  
          if ( extensionJar.isFile() )
          {
              JarFile pluginJar = new JarFile( extensionJar, false );
              try
              {
                  ZipEntry pluginDescriptorEntry = pluginJar.getEntry( getExtensionDescriptorLocation() );
  
                  if ( pluginDescriptorEntry != null )
                  {
                      InputStream is = pluginJar.getInputStream( pluginDescriptorEntry );
  
                      try
                      {
                          extensionDescriptor = build( is );
                      }
                      finally
                      {
                          IOUtil.close( is );
                      }
                  }
              }
              finally
              {
                  pluginJar.close();
              }
          }
          else
          {
              File pluginXml = new File( extensionJar, getExtensionDescriptorLocation() );
  
              if ( pluginXml.canRead() )
              {
                  InputStream is = new BufferedInputStream( new FileInputStream( pluginXml ) );
                  try
                 {
                     extensionDescriptor = build( is );
                 }
                 finally
                 {
                     IOUtil.close( is );
                 }
             }
         }
 
         return extensionDescriptor;
     }
 
     /**
      * @since 3.3.0
      */
     public ExtensionDescriptor build( InputStream is )
         throws IOException
     {
         ExtensionDescriptor extensionDescriptor = new ExtensionDescriptor();
 
         Xpp3Dom dom;
         try
         {
             dom = Xpp3DomBuilder.build( ReaderFactory.newXmlReader( is ) );
         }
         catch ( XmlPullParserException e )
         {
             throw (IOException) new IOException( e.getMessage() ).initCause( e );
         }
 
         if ( !"extension".equals( dom.getName() ) )
         {
             throw new IOException( "Unexpected root element \"" + dom.getName() + "\", expected \"extension\"" );
         }
 
         extensionDescriptor.setExportedPackages( parseStrings( dom.getChild( "exportedPackages" ) ) );
 
         extensionDescriptor.setExportedArtifacts( parseStrings( dom.getChild( "exportedArtifacts" ) ) );
 
         return extensionDescriptor;
     }
 
     private List<String> parseStrings( Xpp3Dom dom )
     {
         List<String> strings = null;
 
         if ( dom != null )
         {
             strings = new ArrayList<String>();
 
             for ( Xpp3Dom child : dom.getChildren() )
             {
                 String string = child.getValue();
                 if ( string != null )
                 {
                     string = string.trim();
                     if ( string.length() > 0 )
                     {
                         strings.add( string );
                     }
                 }
             }
         }
 
         return strings;
     }
 
 }