package org.apache.maven.plugin.plugin;
   
   /*
    * 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.File;
  import java.io.FileNotFoundException;
  import java.io.FileReader;
  import java.util.ArrayList;
  import java.util.Iterator;
  import java.util.LinkedHashSet;
  import java.util.List;
  import java.util.Locale;
  import java.util.Map;
  import java.util.ResourceBundle;
  
  import org.apache.maven.artifact.repository.ArtifactRepository;
  import org.apache.maven.doxia.sink.Sink;
  import org.apache.maven.doxia.siterenderer.Renderer;
  import org.apache.maven.model.Plugin;
  import org.apache.maven.plugin.descriptor.InvalidPluginDescriptorException;
  import org.apache.maven.plugin.descriptor.MojoDescriptor;
  import org.apache.maven.plugin.descriptor.PluginDescriptor;
  import org.apache.maven.plugin.descriptor.PluginDescriptorBuilder;
  import org.apache.maven.plugins.annotations.Component;
  import org.apache.maven.plugins.annotations.Execute;
  import org.apache.maven.plugins.annotations.LifecyclePhase;
  import org.apache.maven.plugins.annotations.Mojo;
  import org.apache.maven.plugins.annotations.Parameter;
  import org.apache.maven.plugins.plugin.descriptor.MNG6109PluginDescriptorBuilder;
  import org.apache.maven.project.MavenProject;
  import org.apache.maven.reporting.AbstractMavenReport;
  import org.apache.maven.reporting.AbstractMavenReportRenderer;
  import org.apache.maven.reporting.MavenReportException;
  import org.apache.maven.rtinfo.RuntimeInformation;
  import org.apache.maven.tools.plugin.DefaultPluginToolsRequest;
  import org.apache.maven.tools.plugin.PluginToolsRequest;
  import org.apache.maven.tools.plugin.extractor.ExtractionException;
  import org.apache.maven.tools.plugin.generator.GeneratorException;
  import org.apache.maven.tools.plugin.generator.GeneratorUtils;
  import org.apache.maven.tools.plugin.generator.PluginXdocGenerator;
  import org.apache.maven.tools.plugin.scanner.MojoScanner;
  import org.apache.maven.tools.plugin.util.PluginUtils;
  import org.codehaus.plexus.component.repository.ComponentDependency;
  import org.codehaus.plexus.configuration.PlexusConfigurationException;
  import org.codehaus.plexus.util.StringUtils;
  import org.codehaus.plexus.util.xml.Xpp3Dom;
  
  /**
   * Generates the Plugin's documentation report: <code>plugin-info.html</code> plugin overview page,
   * and one <code><i>goal</i>-mojo.html</code> per goal.
   *
   * @author <a href="snicoll@apache.org">Stephane Nicoll</a>
   * @author <a href="mailto:vincent.siveton@gmail.com">Vincent Siveton</a>
   * @since 2.0
   */
  @Mojo( name = "report", threadSafe = true )
  @Execute( phase = LifecyclePhase.PROCESS_CLASSES )
  public class PluginReport
      extends AbstractMavenReport
  {
      /**
       * Report output directory for mojos' documentation.
       */
      @Parameter( defaultValue = "${project.build.directory}/generated-site/xdoc" )
      private File outputDirectory;
  
      /**
       * Doxia Site Renderer.
       */
      @Component
      private Renderer siteRenderer;
  
      /**
       * The Maven Project.
       */
      @Parameter( defaultValue = "${project}", readonly = true )
      private MavenProject project;
  
      /**
       * Mojo scanner tools.
       */
      @Component
     protected MojoScanner mojoScanner;
 
     /**
      * The file encoding of the source files.
      *
      * @since 2.7
      */
     @Parameter( property = "encoding", defaultValue = "${project.build.sourceEncoding}" )
     private String encoding;
 
     /**
      * Specify some requirements to execute this plugin.
      * Example:
      * <pre>
      * &lt;requirements&gt;
      *   &lt;maven&gt;2.0&lt;/maven&gt;
      *   &lt;jdk&gt;1.4&lt;/jdk&gt;
      *   &lt;memory&gt;256m&lt;/memory&gt;
      *   &lt;diskSpace&gt;1m&lt;/diskSpace&gt;
      *   &lt;others&gt;
      *     &lt;property&gt;
      *       &lt;name&gt;SVN&lt;/name&gt;
      *       &lt;value&gt;1.4.6&lt;/value&gt;
      *     &lt;/property&gt;
      *   &lt;/others&gt;
      * &lt;/requirements&gt;
      * </pre>
      * 
      * If not is specified, Maven requirement is extracted from
      * <code>&lt;project&gt;&lt;prerequisites&gt;&lt;maven&gt;</code>
      * and JDK requirement is extracted from maven-compiler-plugin configuration.
      */
     @Parameter
     private Requirements requirements;
 
     /**
      * <p>
      * The goal prefix that will appear before the ":".
      * By default, this plugin applies a heuristic to derive a heuristic from
      * the plugin's artifactId.
      * </p>
      * <p>
      * It removes any occurrences of the regular expression <strong>-?maven-?</strong>,
      * and then removes any occurrences of <strong>-?plugin-?</strong>.
      * </p>
      * <p>
      * For example, horsefeature-maven-plugin becomes horsefeature.
      * </p>
      * <p>
      * (There is a special case for maven-plugin-plugin: it is mapped to 'plugin')
      * </p>
      *
      * @since 2.4
      */
     @Parameter( property = "goalPrefix" )
     protected String goalPrefix;
 
     /**
      * Set this to "true" to skip invoking any goals or reports of the plugin.
      *
      * @since 2.8
      */
     @Parameter( defaultValue = "false", property = "maven.plugin.skip" )
     private boolean skip;
 
     /**
      * Set this to "true" to skip generating the report.
      *
      * @since 2.8
      */
     @Parameter( defaultValue = "false", property = "maven.plugin.report.skip" )
     private boolean skipReport;
 
     /**
      * List of Remote Repositories used by the resolver
      *
      * @since 3.0
      */
     @Parameter( defaultValue = "${project.remoteArtifactRepositories}", required = true, readonly = true )
     protected List<ArtifactRepository> remoteRepos;
 
     /**
      * Location of the local repository.
      *
      * @since 3.0
      */
     @Parameter( defaultValue = "${localRepository}", required = true, readonly = true )
     protected ArtifactRepository local;
     
     /**
      * @since 3.5.1
      */
     @Component
     private RuntimeInformation rtInfo;
 
     /**
      * Path to {@code plugin.xml} plugin descriptor to generate the report from.
      *
      * @since 3.5.1
      */
     @Parameter( defaultValue = "${project.build.outputDirectory}/META-INF/maven/plugin.xml", required = true,
                     readonly = true )
     private File pluginXmlFile;
 
     /**
      * {@inheritDoc}
      */
     @Override
     protected Renderer getSiteRenderer()
     {
         return siteRenderer;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     protected String getOutputDirectory()
     {
         // PLUGIN-191: output directory of plugin.html, not *-mojo.xml
         return project.getReporting().getOutputDirectory();
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     protected MavenProject getProject()
     {
         return project;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public boolean canGenerateReport()
     {
         return pluginXmlFile != null && pluginXmlFile.isFile() && pluginXmlFile.canRead();
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     protected void executeReport( Locale locale )
         throws MavenReportException
     {
         if ( !canGenerateReport() )
         {
             return;
         }
         if ( skip || skipReport )
         {
             getLog().info( "Maven Plugin Plugin Report generation skipped." );
             return;
         }
 
         PluginDescriptor pluginDescriptor = extractPluginDescriptor();
 
         // Generate the mojos' documentation
         generateMojosDocumentation( pluginDescriptor, locale );
 
         // Write the overview
         PluginOverviewRenderer r =
             new PluginOverviewRenderer( project, requirements, getSink(), pluginDescriptor, locale );
         r.render();
     }
 
     private PluginDescriptor extractPluginDescriptor()
         throws MavenReportException
     {
         PluginDescriptorBuilder builder = getPluginDescriptorBuilder();
         
         try
         {
             return builder.build( new FileReader( pluginXmlFile ) );
         }
         catch ( FileNotFoundException | PlexusConfigurationException e )
         {
             getLog().debug( "Failed to read " + pluginXmlFile + ", fall back to mojoScanner" );
         }
 
         // Copy from AbstractGeneratorMojo#execute()
         String defaultGoalPrefix = PluginDescriptor.getGoalPrefixFromArtifactId( project.getArtifactId() );
         if ( goalPrefix == null )
         {
             goalPrefix = defaultGoalPrefix;
         }
         else
         {
             getLog().warn( "\n\nGoal prefix is specified as: '" + goalPrefix + "'. Maven currently expects it to be '"
                                + defaultGoalPrefix + "'.\n" );
         }
 
         // TODO: could use this more, eg in the writing of the plugin descriptor!
         PluginDescriptor pluginDescriptor = new PluginDescriptor();
 
         pluginDescriptor.setGroupId( project.getGroupId() );
 
         pluginDescriptor.setArtifactId( project.getArtifactId() );
 
         pluginDescriptor.setVersion( project.getVersion() );
 
         pluginDescriptor.setGoalPrefix( goalPrefix );
 
         try
         {
             List<ComponentDependency> deps = GeneratorUtils.toComponentDependencies( project.getArtifacts() );
             pluginDescriptor.setDependencies( deps );
 
             PluginToolsRequest request = new DefaultPluginToolsRequest( project, pluginDescriptor );
             request.setEncoding( encoding );
             request.setSkipErrorNoDescriptorsFound( true );
             request.setDependencies( new LinkedHashSet<>( project.getArtifacts() ) );
             request.setLocal( this.local );
             request.setRemoteRepos( this.remoteRepos );
 
             try
             {
                 mojoScanner.populatePluginDescriptor( request );
             }
             catch ( InvalidPluginDescriptorException e )
             {
                 // this is OK, it happens to lifecycle plugins. Allow generation to proceed.
                 getLog().debug( "Plugin without mojos.", e );
             }
         }
         catch ( ExtractionException e )
         {
             throw new MavenReportException( "Error extracting plugin descriptor: \'" + e.getLocalizedMessage() + "\'",
                                             e );
         }
         return pluginDescriptor;
     }
 
     /**
      * Return the pluginDescriptorBuilder to use based on the Maven version: either use the original from the 
      * maven-plugin-api or a patched version for Maven versions before the MNG-6109 fix 
      * (because of Maven MNG-6109 bug that won't give accurate 'since' info when reading plugin.xml).
      * 
      * @return the proper pluginDescriptorBuilder
      * @see <a href="https://issues.apache.org/jira/browse/MNG-6109">MNG-6109</a>
      * @see <a href="https://issues.apache.org/jira/browse/MPLUGIN-319">MPLUGIN-319</a>
      */
     private PluginDescriptorBuilder getPluginDescriptorBuilder()
     {
         PluginDescriptorBuilder pluginDescriptorBuilder;
 
         if ( rtInfo.isMavenVersion( "(3.3.9,)" ) )
         {
             pluginDescriptorBuilder = new PluginDescriptorBuilder();
         }
         else
         {
             pluginDescriptorBuilder = new MNG6109PluginDescriptorBuilder();
         }
 
         return pluginDescriptorBuilder;
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public String getDescription( Locale locale )
     {
         return getBundle( locale ).getString( "report.plugin.description" );
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public String getName( Locale locale )
     {
         return getBundle( locale ).getString( "report.plugin.name" );
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public String getOutputName()
     {
         return "plugin-info";
     }
 
     /**
      * Generate the mojos documentation, as xdoc files.
      *
      * @param pluginDescriptor not null
      * @param locale           not null
      * @throws MavenReportException if any
      */
     private void generateMojosDocumentation( PluginDescriptor pluginDescriptor, Locale locale )
         throws MavenReportException
     {
         try
         {
             File outputDir = outputDirectory;
             outputDir.mkdirs();
 
             PluginXdocGenerator generator = new PluginXdocGenerator( project, locale );
             PluginToolsRequest pluginToolsRequest = new DefaultPluginToolsRequest( project, pluginDescriptor );
             generator.execute( outputDir, pluginToolsRequest );
         }
         catch ( GeneratorException e )
         {
             throw new MavenReportException( "Error writing plugin documentation", e );
         }
 
     }
 
     /**
      * @param locale not null
      * @return the bundle for this report
      */
     protected static ResourceBundle getBundle( Locale locale )
     {
         return ResourceBundle.getBundle( "plugin-report", locale, PluginReport.class.getClassLoader() );
     }
 
     /**
      * Generates an overview page with the list of goals
      * and a link to the goal's page.
      */
     static class PluginOverviewRenderer
         extends AbstractMavenReportRenderer
     {
         private final MavenProject project;
 
         private final Requirements requirements;
 
         private final PluginDescriptor pluginDescriptor;
 
         private final Locale locale;
 
         /**
          * @param project          not null
          * @param requirements     not null
          * @param sink             not null
          * @param pluginDescriptor not null
          * @param locale           not null
          */
         PluginOverviewRenderer( MavenProject project, Requirements requirements, Sink sink,
                                 PluginDescriptor pluginDescriptor, Locale locale )
         {
             super( sink );
 
             this.project = project;
 
             this.requirements = ( requirements == null ? new Requirements() : requirements );
 
             this.pluginDescriptor = pluginDescriptor;
 
             this.locale = locale;
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         public String getTitle()
         {
             return getBundle( locale ).getString( "report.plugin.title" );
         }
 
         /**
          * {@inheritDoc}
          */
         @Override
         @SuppressWarnings( { "unchecked", "rawtypes" } )
         public void renderBody()
         {
             startSection( getTitle() );
 
             if ( !( pluginDescriptor.getMojos() != null && pluginDescriptor.getMojos().size() > 0 ) )
             {
                 paragraph( getBundle( locale ).getString( "report.plugin.goals.nogoal" ) );
                 endSection();
                 return;
             }
 
             paragraph( getBundle( locale ).getString( "report.plugin.goals.intro" ) );
 
             boolean hasMavenReport = false;
             for ( Iterator<MojoDescriptor> i = pluginDescriptor.getMojos().iterator(); i.hasNext(); )
             {
                 MojoDescriptor mojo = i.next();
 
                 if ( GeneratorUtils.isMavenReport( mojo.getImplementation(), project ) )
                 {
                     hasMavenReport = true;
                 }
             }
 
             startTable();
 
             String goalColumnName = getBundle( locale ).getString( "report.plugin.goals.column.goal" );
             String isMavenReport = getBundle( locale ).getString( "report.plugin.goals.column.isMavenReport" );
             String descriptionColumnName = getBundle( locale ).getString( "report.plugin.goals.column.description" );
             if ( hasMavenReport )
             {
                 tableHeader( new String[]{ goalColumnName, isMavenReport, descriptionColumnName } );
             }
             else
             {
                 tableHeader( new String[]{ goalColumnName, descriptionColumnName } );
             }
 
             List<MojoDescriptor> mojos = new ArrayList<>();
             mojos.addAll( pluginDescriptor.getMojos() );
             PluginUtils.sortMojos( mojos );
             for ( MojoDescriptor mojo : mojos )
             {
                 String goalName = mojo.getFullGoalName();
 
                 /*
                  * Added ./ to define a relative path
                  * @see AbstractMavenReportRenderer#getValidHref(java.lang.String)
                  */
                 String goalDocumentationLink = "./" + mojo.getGoal() + "-mojo.html";
 
                 String description;
                 if ( StringUtils.isNotEmpty( mojo.getDeprecated() ) )
                 {
                     description =
                         "<strong>" + getBundle( locale ).getString( "report.plugin.goal.deprecated" ) + "</strong> "
                             + GeneratorUtils.makeHtmlValid( mojo.getDeprecated() );
                 }
                 else if ( StringUtils.isNotEmpty( mojo.getDescription() ) )
                 {
                     description = GeneratorUtils.makeHtmlValid( mojo.getDescription() );
                 }
                 else
                 {
                     description = getBundle( locale ).getString( "report.plugin.goal.nodescription" );
                 }
 
                 sink.tableRow();
                 tableCell( createLinkPatternedText( goalName, goalDocumentationLink ) );
                 if ( hasMavenReport )
                 {
                     if ( GeneratorUtils.isMavenReport( mojo.getImplementation(), project ) )
                     {
                         sink.tableCell();
                         sink.text( getBundle( locale ).getString( "report.plugin.isReport" ) );
                         sink.tableCell_();
                     }
                     else
                     {
                         sink.tableCell();
                         sink.text( getBundle( locale ).getString( "report.plugin.isNotReport" ) );
                         sink.tableCell_();
                     }
                 }
                 tableCell( description, true );
                 sink.tableRow_();
             }
 
             endTable();
 
             startSection( getBundle( locale ).getString( "report.plugin.systemrequirements" ) );
 
             paragraph( getBundle( locale ).getString( "report.plugin.systemrequirements.intro" ) );
 
             startTable();
 
             String maven = discoverMavenRequirement( project, requirements );
             sink.tableRow();
             tableCell( getBundle( locale ).getString( "report.plugin.systemrequirements.maven" ) );
             tableCell( ( maven != null
                 ? maven
                 : getBundle( locale ).getString( "report.plugin.systemrequirements.nominimum" ) ) );
             sink.tableRow_();
 
             String jdk = discoverJdkRequirement( project, requirements );
             sink.tableRow();
             tableCell( getBundle( locale ).getString( "report.plugin.systemrequirements.jdk" ) );
             tableCell(
                 ( jdk != null ? jdk : getBundle( locale ).getString( "report.plugin.systemrequirements.nominimum" ) ) );
             sink.tableRow_();
 
             sink.tableRow();
             tableCell( getBundle( locale ).getString( "report.plugin.systemrequirements.memory" ) );
             tableCell( ( StringUtils.isNotEmpty( requirements.getMemory() )
                 ? requirements.getMemory()
                 : getBundle( locale ).getString( "report.plugin.systemrequirements.nominimum" ) ) );
             sink.tableRow_();
 
             sink.tableRow();
             tableCell( getBundle( locale ).getString( "report.plugin.systemrequirements.diskspace" ) );
             tableCell( ( StringUtils.isNotEmpty( requirements.getDiskSpace() )
                 ? requirements.getDiskSpace()
                 : getBundle( locale ).getString( "report.plugin.systemrequirements.nominimum" ) ) );
             sink.tableRow_();
 
             if ( requirements.getOthers() != null && requirements.getOthers().size() > 0 )
             {
                 for ( Iterator it = requirements.getOthers().keySet().iterator(); it.hasNext(); )
                 {
                     String key = it.next().toString();
 
                     sink.tableRow();
                     tableCell( key );
                     tableCell( ( StringUtils.isNotEmpty( requirements.getOthers().getProperty( key ) )
                         ? requirements.getOthers().getProperty( key )
                         : getBundle( locale ).getString( "report.plugin.systemrequirements.nominimum" ) ) );
                     sink.tableRow_();
                 }
             }
             endTable();
 
             endSection();
 
             renderUsageSection( hasMavenReport );
 
             endSection();
         }
 
         /**
          * Render the section about the usage of the plugin.
          *
          * @param hasMavenReport If the plugin has a report or not
          */
         private void renderUsageSection( boolean hasMavenReport )
         {
             startSection( getBundle( locale ).getString( "report.plugin.usage" ) );
 
             // Configuration
             sink.paragraph();
             text( getBundle( locale ).getString( "report.plugin.usage.intro" ) );
             sink.paragraph_();
 
             StringBuilder sb = new StringBuilder();
             sb.append( "<project>" ).append( '\n' );
             sb.append( "  ..." ).append( '\n' );
             sb.append( "  <build>" ).append( '\n' );
             sb.append(
                 "    <!-- " + getBundle( locale ).getString( "report.plugin.usage.pluginManagement" ) + " -->" ).append(
                 '\n' );
             sb.append( "    <pluginManagement>" ).append( '\n' );
             sb.append( "      <plugins>" ).append( '\n' );
             sb.append( "        <plugin>" ).append( '\n' );
             sb.append( "          <groupId>" ).append( pluginDescriptor.getGroupId() ).append( "</groupId>" ).append(
                 '\n' );
             sb.append( "          <artifactId>" ).append( pluginDescriptor.getArtifactId() ).append(
                 "</artifactId>" ).append( '\n' );
             sb.append( "          <version>" ).append( pluginDescriptor.getVersion() ).append( "</version>" ).append(
                 '\n' );
             sb.append( "        </plugin>" ).append( '\n' );
             sb.append( "        ..." ).append( '\n' );
             sb.append( "      </plugins>" ).append( '\n' );
             sb.append( "    </pluginManagement>" ).append( '\n' );
             sb.append( "    <!-- " + getBundle( locale ).getString( "report.plugin.usage.plugins" ) + " -->" ).append(
                 '\n' );
             sb.append( "    <plugins>" ).append( '\n' );
             sb.append( "      <plugin>" ).append( '\n' );
             sb.append( "        <groupId>" ).append( pluginDescriptor.getGroupId() ).append( "</groupId>" ).append(
                 '\n' );
             sb.append( "        <artifactId>" ).append( pluginDescriptor.getArtifactId() ).append(
                 "</artifactId>" ).append( '\n' );
             sb.append( "        <version>" ).append( pluginDescriptor.getVersion() ).append( "</version>" ).append(
                 '\n' );
             sb.append( "      </plugin>" ).append( '\n' );
             sb.append( "      ..." ).append( '\n' );
             sb.append( "    </plugins>" ).append( '\n' );
             sb.append( "  </build>" ).append( '\n' );
 
             if ( hasMavenReport )
             {
                 sb.append( "  ..." ).append( '\n' );
                 sb.append(
                     "  <!-- " + getBundle( locale ).getString( "report.plugin.usage.reporting" ) + " -->" ).append(
                     '\n' );
                 sb.append( "  <reporting>" ).append( '\n' );
                 sb.append( "    <plugins>" ).append( '\n' );
                 sb.append( "      <plugin>" ).append( '\n' );
                 sb.append( "        <groupId>" ).append( pluginDescriptor.getGroupId() ).append( "</groupId>" ).append(
                     '\n' );
                 sb.append( "        <artifactId>" ).append( pluginDescriptor.getArtifactId() ).append(
                     "</artifactId>" ).append( '\n' );
                 sb.append( "        <version>" ).append( pluginDescriptor.getVersion() ).append( "</version>" ).append(
                     '\n' );
                 sb.append( "      </plugin>" ).append( '\n' );
                 sb.append( "      ..." ).append( '\n' );
                 sb.append( "    </plugins>" ).append( '\n' );
                 sb.append( "  </reporting>" ).append( '\n' );
             }
 
             sb.append( "  ..." ).append( '\n' );
             sb.append( "</project>" ).append( '\n' );
 
             verbatimText( sb.toString() );
 
             sink.paragraph();
             linkPatternedText( getBundle( locale ).getString( "report.plugin.configuration.end" ) );
             sink.paragraph_();
 
             endSection();
         }
 
         /**
          * Try to lookup on the Maven prerequisites property.
          * If not specified, uses the value defined by the user.
          *
          * @param project      not null
          * @param requirements not null
          * @return the Maven version
          */
         private static String discoverMavenRequirement( MavenProject project, Requirements requirements )
         {
             String maven = requirements.getMaven();
             if ( maven == null )
             {
                 maven = ( project.getPrerequisites() != null ? project.getPrerequisites().getMaven() : null );
             }
             if ( maven == null )
             {
                 maven = "2.0";
             }
 
             return maven;
         }
 
         /**
          * <ol>
          * <li>use configured jdk requirement</li>
          * <li>use <code>target</code> configuration of <code>org.apache.maven.plugins:maven-compiler-plugin</code></li>
          * <li>use <code>target</code> configuration of <code>org.apache.maven.plugins:maven-compiler-plugin</code> in
          * <code>pluginManagement</code></li>
          * <li>use <code>maven.compiler.target</code> property</li>
          * </ol>
          *
          * @param project      not null
          * @param requirements not null
          * @return the JDK version
          */
         private static String discoverJdkRequirement( MavenProject project, Requirements requirements )
         {
             String jdk = requirements.getJdk();
 
             if ( jdk != null )
             {
                 return jdk;
             }
 
             Plugin compiler = getCompilerPlugin( project.getBuild().getPluginsAsMap() );
             if ( compiler == null )
             {
                 compiler = getCompilerPlugin( project.getPluginManagement().getPluginsAsMap() );
             }
 
             jdk = getPluginParameter( compiler, "target" );
             if ( jdk != null )
             {
                 return jdk;
             }
 
             jdk = getPluginParameter( compiler, "release" );
             if ( jdk != null )
             {
                 return jdk;
             }
 
             // default value
             jdk = project.getProperties().getProperty( "maven.compiler.target" );
             if ( jdk != null )
             {
                 return jdk;
             }
 
             // return "1.5" by default?
 
             String version = ( compiler == null ) ? null : compiler.getVersion();
 
             if ( version != null )
             {
                 return "Default target for maven-compiler-plugin version " + version;
             }
 
             return "Unknown";
         }
 
         private static Plugin getCompilerPlugin( Map<String, Plugin> pluginsAsMap )
         {
             return pluginsAsMap.get( "org.apache.maven.plugins:maven-compiler-plugin" );
         }
 
         private static String getPluginParameter( Plugin plugin, String parameter )
         {
             if ( plugin != null )
             {
                 Xpp3Dom pluginConf = (Xpp3Dom) plugin.getConfiguration();
 
                 if ( pluginConf != null )
                 {
                     Xpp3Dom target = pluginConf.getChild( parameter );
 
                     if ( target != null )
                     {
                         return target.getValue();
                     }
                 }
             }
 
             return null;
         }
     }
 }