import org.apache.maven.plugin.AbstractMojo;
   import org.apache.maven.plugin.MojoExecutionException;
   import org.apache.maven.plugins.annotations.Mojo;
   import org.apache.maven.plugins.annotations.Parameter;
   
   import org.w3c.dom.Document;
   import org.w3c.dom.Element;
  import org.w3c.dom.Node;
  import org.w3c.dom.NodeList;
  import org.xml.sax.SAXException;
  
  import javax.xml.parsers.DocumentBuilder;
  import javax.xml.parsers.DocumentBuilderFactory;
  import javax.xml.parsers.ParserConfigurationException;
  import java.io.IOException;
  import java.io.InputStream;
  import java.util.ArrayList;
  import java.util.List;
  
  /**
   * Display help information on maven-plugin-plugin.<br>
   * Call <code>mvn plugin:help -Ddetail=true -Dgoal=&lt;goal-name&gt;</code> to display parameter details.
   * @author maven-plugin-tools
   */
  @Mojo( name = "help", requiresProject = false, threadSafe = true )
  public class HelpMojo
      extends AbstractMojo
  {
      /**
       * If <code>true</code>, display all settable properties for each goal.
       *
       */
      @Parameter( property = "detail", defaultValue = "false" )
      private boolean detail;
  
      /**
       * The name of the goal for which to show help. If unspecified, all goals will be displayed.
       *
       */
      @Parameter( property = "goal" )
      private java.lang.String goal;
  
      /**
       * The maximum length of a display line, should be positive.
       *
       */
      @Parameter( property = "lineLength", defaultValue = "80" )
      private int lineLength;
  
      /**
       * The number of spaces per indentation level, should be positive.
       *
       */
      @Parameter( property = "indentSize", defaultValue = "2" )
      private int indentSize;
  
      // groupId/artifactId/plugin-help.xml
      private static final String PLUGIN_HELP_PATH =
                      "/META-INF/maven/org.apache.maven.plugins/maven-plugin-plugin/plugin-help.xml";
  
      private static final int DEFAULT_LINE_LENGTH = 80;
  
      private Document build()
          throws MojoExecutionException
      {
          getLog().debug( "load plugin-help.xml: " + PLUGIN_HELP_PATH );
          InputStream is = null;
          try
          {
              is = getClass().getResourceAsStream( PLUGIN_HELP_PATH );
              DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
              DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
              return dBuilder.parse( is );
          }
          catch ( IOException e )
          {
              throw new MojoExecutionException( e.getMessage(), e );
          }
          catch ( ParserConfigurationException e )
          {
              throw new MojoExecutionException( e.getMessage(), e );
          }
          catch ( SAXException e )
          {
              throw new MojoExecutionException( e.getMessage(), e );
          }
          finally
          {
              if ( is != null )
              {
                  try
                  {
                      is.close();
                  }
                  catch ( IOException e )
                  {
                      throw new MojoExecutionException( e.getMessage(), e );
                 }
             }
         }
     }
 
     /**
      * {@inheritDoc}
      */
     public void execute()
         throws MojoExecutionException
     {
         if ( lineLength <= 0 )
         {
             getLog().warn( "The parameter 'lineLength' should be positive, using '80' as default." );
             lineLength = DEFAULT_LINE_LENGTH;
         }
         if ( indentSize <= 0 )
         {
             getLog().warn( "The parameter 'indentSize' should be positive, using '2' as default." );
             indentSize = 2;
         }
 
         Document doc = build();
 
         StringBuilder sb = new StringBuilder();
         Node plugin = getSingleChild( doc, "plugin" );
 
 
         String name = getValue( plugin, "name" );
         String version = getValue( plugin, "version" );
         String id = getValue( plugin, "groupId" ) + ":" + getValue( plugin, "artifactId" ) + ":" + version;
         if ( isNotEmpty( name ) && !name.contains( id ) )
         {
             append( sb, name + " " + version, 0 );
         }
         else
         {
             if ( isNotEmpty( name ) )
             {
                 append( sb, name, 0 );
             }
             else
             {
                 append( sb, id, 0 );
             }
         }
         append( sb, getValue( plugin, "description" ), 1 );
         append( sb, "", 0 );
 
         //<goalPrefix>plugin</goalPrefix>
         String goalPrefix = getValue( plugin, "goalPrefix" );
 
         Node mojos1 = getSingleChild( plugin, "mojos" );
 
         List<Node> mojos = findNamedChild( mojos1, "mojo" );
 
         if ( goal == null || goal.length() <= 0 )
         {
             append( sb, "This plugin has " + mojos.size() + ( mojos.size() > 1 ? " goals:" : " goal:" ), 0 );
             append( sb, "", 0 );
         }
 
         for ( Node mojo : mojos )
         {
             writeGoal( sb, goalPrefix, (Element) mojo );
         }
 
         if ( getLog().isInfoEnabled() )
         {
             getLog().info( sb.toString() );
         }
     }
 
 
     private static boolean isNotEmpty( String string )
     {
         return string != null && string.length() > 0;
     }
 
     private String getValue( Node node, String elementName )
         throws MojoExecutionException
     {
         return getSingleChild( node, elementName ).getTextContent();
     }
 
     private Node getSingleChild( Node node, String elementName )
         throws MojoExecutionException
     {
         List<Node> namedChild = findNamedChild( node, elementName );
         if ( namedChild.isEmpty() )
         {
             throw new MojoExecutionException( "Could not find " + elementName + " in plugin-help.xml" );
         }
         if ( namedChild.size() > 1 )
         {
             throw new MojoExecutionException( "Multiple " + elementName + " in plugin-help.xml" );
         }
         return namedChild.get( 0 );
     }
 
     private List<Node> findNamedChild( Node node, String elementName )
     {
         List<Node> result = new ArrayList<Node>();
         NodeList childNodes = node.getChildNodes();
         for ( int i = 0; i < childNodes.getLength(); i++ )
         {
             Node item = childNodes.item( i );
             if ( elementName.equals( item.getNodeName() ) )
             {
                 result.add( item );
             }
         }
         return result;
     }
 
     private Node findSingleChild( Node node, String elementName )
         throws MojoExecutionException
     {
         List<Node> elementsByTagName = findNamedChild( node, elementName );
         if ( elementsByTagName.isEmpty() )
         {
             return null;
         }
         if ( elementsByTagName.size() > 1 )
         {
             throw new MojoExecutionException( "Multiple " + elementName + "in plugin-help.xml" );
         }
         return elementsByTagName.get( 0 );
     }
 
     private void writeGoal( StringBuilder sb, String goalPrefix, Element mojo )
         throws MojoExecutionException
     {
         String mojoGoal = getValue( mojo, "goal" );
         Node configurationElement = findSingleChild( mojo, "configuration" );
         Node description = findSingleChild( mojo, "description" );
         if ( goal == null || goal.length() <= 0 || mojoGoal.equals( goal ) )
         {
             append( sb, goalPrefix + ":" + mojoGoal, 0 );
             Node deprecated = findSingleChild( mojo, "deprecated" );
             if ( ( deprecated != null ) && isNotEmpty( deprecated.getTextContent() ) )
             {
                 append( sb, "Deprecated. " + deprecated.getTextContent(), 1 );
                 if ( detail && description != null )
                 {
                     append( sb, "", 0 );
                     append( sb, description.getTextContent(), 1 );
                 }
             }
             else if ( description != null )
             {
                 append( sb, description.getTextContent(), 1 );
             }
             append( sb, "", 0 );
 
             if ( detail )
             {
                 Node parametersNode = getSingleChild( mojo, "parameters" );
                 List<Node> parameters = findNamedChild( parametersNode, "parameter" );
                 append( sb, "Available parameters:", 1 );
                 append( sb, "", 0 );
 
                 for ( Node parameter : parameters )
                 {
                     writeParameter( sb, parameter, configurationElement );
                 }
             }
         }
     }
 
     private void writeParameter( StringBuilder sb, Node parameter, Node configurationElement )
         throws MojoExecutionException
     {
         String parameterName = getValue( parameter, "name" );
         String parameterDescription = getValue( parameter, "description" );
 
         Element fieldConfigurationElement = (Element) findSingleChild( configurationElement, parameterName );
 
         String parameterDefaultValue = "";
         if ( fieldConfigurationElement != null && fieldConfigurationElement.hasAttribute( "default-value" ) )
         {
             parameterDefaultValue = " (Default: " + fieldConfigurationElement.getAttribute( "default-value" ) + ")";
         }
         append( sb, parameterName + parameterDefaultValue, 2 );
         Node deprecated = findSingleChild( parameter, "deprecated" );
         if ( ( deprecated != null ) && isNotEmpty( deprecated.getTextContent() ) )
         {
             append( sb, "Deprecated. " + deprecated.getTextContent(), 3 );
             append( sb, "", 0 );
         }
         append( sb, parameterDescription, 3 );
         if ( "true".equals( getValue( parameter, "required" ) ) )
         {
             append( sb, "Required: Yes", 3 );
         }
         if ( ( fieldConfigurationElement != null ) && isNotEmpty( fieldConfigurationElement.getTextContent() ) )
         {
             String property = getPropertyFromExpression( fieldConfigurationElement.getTextContent() );
             append( sb, "User property: " + property, 3 );
         }
 
         append( sb, "", 0 );
     }
 
     /**
      * <p>Repeat a String <code>n</code> times to form a new string.</p>
      *
      * @param str    String to repeat
      * @param repeat number of times to repeat str
      * @return String with repeated String
      * @throws NegativeArraySizeException if <code>repeat < 0</code>
      * @throws NullPointerException       if str is <code>null</code>
      */
     private static String repeat( String str, int repeat )
     {
         StringBuilder buffer = new StringBuilder( repeat * str.length() );
 
         for ( int i = 0; i < repeat; i++ )
         {
             buffer.append( str );
         }
 
         return buffer.toString();
     }
 
     /**
      * Append a description to the buffer by respecting the indentSize and lineLength parameters.
      * <b>Note</b>: The last character is always a new line.
      *
      * @param sb          The buffer to append the description, not <code>null</code>.
      * @param description The description, not <code>null</code>.
      * @param indent      The base indentation level of each line, must not be negative.
      */
     private void append( StringBuilder sb, String description, int indent )
     {
         for ( String line : toLines( description, indent, indentSize, lineLength ) )
         {
             sb.append( line ).append( '\n' );
         }
     }
 
     /**
      * Splits the specified text into lines of convenient display length.
      *
      * @param text       The text to split into lines, must not be <code>null</code>.
      * @param indent     The base indentation level of each line, must not be negative.
      * @param indentSize The size of each indentation, must not be negative.
      * @param lineLength The length of the line, must not be negative.
      * @return The sequence of display lines, never <code>null</code>.
      * @throws NegativeArraySizeException if <code>indent < 0</code>
      */
     private static List<String> toLines( String text, int indent, int indentSize, int lineLength )
     {
         List<String> lines = new ArrayList<String>();
 
         String ind = repeat( "\t", indent );
 
         String[] plainLines = text.split( "(\r\n)|(\r)|(\n)" );
 
         for ( String plainLine : plainLines )
         {
             toLines( lines, ind + plainLine, indentSize, lineLength );
         }
 
         return lines;
     }
 
     /**
      * Adds the specified line to the output sequence, performing line wrapping if necessary.
      *
      * @param lines      The sequence of display lines, must not be <code>null</code>.
      * @param line       The line to add, must not be <code>null</code>.
      * @param indentSize The size of each indentation, must not be negative.
      * @param lineLength The length of the line, must not be negative.
      */
     private static void toLines( List<String> lines, String line, int indentSize, int lineLength )
     {
         int lineIndent = getIndentLevel( line );
         StringBuilder buf = new StringBuilder( 256 );
 
         String[] tokens = line.split( " +" );
 
         for ( String token : tokens )
         {
             if ( buf.length() > 0 )
             {
                 if ( buf.length() + token.length() >= lineLength )
                 {
                     lines.add( buf.toString() );
                     buf.setLength( 0 );
                     buf.append( repeat( " ", lineIndent * indentSize ) );
                 }
                 else
                 {
                     buf.append( ' ' );
                 }
             }
 
             for ( int j = 0; j < token.length(); j++ )
             {
                 char c = token.charAt( j );
                 if ( c == '\t' )
                 {
                     buf.append( repeat( " ", indentSize - buf.length() % indentSize ) );
                 }
                 else if ( c == '\u00A0' )
                 {
                     buf.append( ' ' );
                 }
                 else
                 {
                     buf.append( c );
                 }
             }
         }
         lines.add( buf.toString() );
     }
 
     /**
      * Gets the indentation level of the specified line.
      *
      * @param line The line whose indentation level should be retrieved, must not be <code>null</code>.
      * @return The indentation level of the line.
      */
     private static int getIndentLevel( String line )
     {
         int level = 0;
         for ( int i = 0; i < line.length() && line.charAt( i ) == '\t'; i++ )
         {
             level++;
         }
         for ( int i = level + 1; i <= level + 4 && i < line.length(); i++ )
         {
             if ( line.charAt( i ) == '\t' )
             {
                 level++;
                 break;
             }
         }
         return level;
     }
     
     private String getPropertyFromExpression( String expression )
     {
         if ( expression != null && expression.startsWith( "${" ) && expression.endsWith( "}" )
             && !expression.substring( 2 ).contains( "${" ) )
         {
             // expression="${xxx}" -> property="xxx"
             return expression.substring( 2, expression.length() - 1 );
         }
         // no property can be extracted
         return null;
     }
 }