import org.apache.maven.plugin.AbstractMojo;

 import org.apache.maven.plugin.MojoExecutionException;

 import org.codehaus.plexus.util.ReaderFactory;

 import org.codehaus.plexus.util.StringUtils;

 import org.codehaus.plexus.util.xml.Xpp3Dom;

 import org.codehaus.plexus.util.xml.Xpp3DomBuilder;

 import org.codehaus.plexus.util.xml.pull.XmlPullParserException;

 import java.io.IOException;

 import java.io.InputStream;

 import java.util.ArrayList;

 import java.util.Iterator;

 import java.util.List;

 /**

  * Display help information on maven-invoker-plugin.<br/>

  * Call <code>mvn invoker:help -Ddetail=true -Dgoal=&lt;goal-name&gt;</code> to display parameter details.

  * @author

  * @version

  * @goal help

  * @requiresProject false

  * @threadSafe

  */

 public class HelpMojo

     extends AbstractMojo

 {

     /**

      * If <code>true</code>, display all settable properties for each goal.

      *

      * @parameter property="detail" default-value="false"

      */

     //@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"

      */

     //@Parameter( property = "goal" )

     private java.lang.String goal;

     /**

      * The maximum length of a display line, should be positive.

      *

      * @parameter property="lineLength" default-value="80"

      */

     //@Parameter( property = "lineLength", defaultValue = "80" )

     private int lineLength;

     /**

      * The number of spaces per indentation level, should be positive.

      *

      * @parameter property="indentSize" default-value="2"

      */

     //@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-invoker-plugin/plugin-help.xml";

     private Xpp3Dom build()

         throws MojoExecutionException

     {

         getLog().debug( "load plugin-help.xml: " + PLUGIN_HELP_PATH );

         InputStream is = getClass().getResourceAsStream( PLUGIN_HELP_PATH );

         try

         {

             return Xpp3DomBuilder.build( ReaderFactory.newXmlReader( is ) );

         }

         catch ( XmlPullParserException e )

         {

             throw new MojoExecutionException( e.getMessage(), e );

         }

         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 = 80;

         }

         if ( indentSize <= 0 )

         {

             getLog().warn( "The parameter 'indentSize' should be positive, using '2' as default." );

             indentSize = 2;

         }

         Xpp3Dom pluginElement = build();

         StringBuilder sb = new StringBuilder();

         String name = pluginElement.getChild( "name" ).getValue();

         String version = pluginElement.getChild( "version" ).getValue();

         String id = pluginElement.getChild( "groupId" ).getValue() + ":" + pluginElement.getChild( "artifactId" ).getValue()

                     + ":" + version;

         if ( StringUtils.isNotEmpty( name ) && !name.contains( id ) )

         {

             append( sb, name + " " + version, 0 );

         }

         else

         {

             if ( StringUtils.isNotEmpty( name ) )

             {

                 append( sb, name, 0 );

             }

             else

             {

                 append( sb, id, 0 );

             }

         }

         append( sb, pluginElement.getChild( "description" ).getValue(), 1 );

         append( sb, "", 0 );

         //<goalPrefix>plugin</goalPrefix>

         String goalPrefix = pluginElement.getChild( "goalPrefix" ).getValue();

         Xpp3Dom[] mojos = pluginElement.getChild( "mojos" ).getChildren( "mojo" );

         if ( goal == null || goal.length() <= 0 )

         {

             append( sb, "This plugin has " + mojos.length + ( mojos.length > 1 ? " goals:" : " goal:" ) , 0 );

             append( sb, "", 0 );

         }

         for ( Xpp3Dom mojo : mojos )

         {

             writeGoal( sb, goalPrefix, mojo );

         }

         if ( getLog().isInfoEnabled() )

         {

             getLog().info( sb.toString() );

         }

     }

     private String getValue( Xpp3Dom mojo, String child )

     {

         Xpp3Dom elt = mojo.getChild( child );

         return ( elt == null ) ? "" : elt.getValue();

     }

     private void writeGoal( StringBuilder sb, String goalPrefix, Xpp3Dom mojo )

     {

         String mojoGoal = mojo.getChild( "goal" ).getValue();

         Xpp3Dom configurationElement = mojo.getChild( "configuration" );

         if ( goal == null || goal.length() <= 0 || mojoGoal.equals( goal ) )

         {

             append( sb, goalPrefix + ":" + mojoGoal, 0 );

             Xpp3Dom deprecated = mojo.getChild( "deprecated" );

             if ( ( deprecated != null ) && StringUtils.isNotEmpty( deprecated.getValue() ) )

             {

                 append( sb, "Deprecated. " + deprecated, 1 );

                 if ( detail )

                 {

                     append( sb, "", 0 );

                     append( sb, getValue( mojo, "description" ), 1 );

                 }

             }

             else

             {

                 append( sb, getValue( mojo, "description" ), 1 );

             }

             append( sb, "", 0 );

             if ( detail )

             {

                 Xpp3Dom[] parameters = mojo.getChild( "parameters" ).getChildren( "parameter" );

                 append( sb, "Available parameters:", 1 );

                 append( sb, "", 0 );

                 for ( Xpp3Dom parameter : parameters )

                 {

                     writeParameter( sb, parameter, configurationElement );

                 }

             }

         }

     }

     private void writeParameter( StringBuilder sb, Xpp3Dom parameter, Xpp3Dom configurationElement )

     {

         String parameterName = parameter.getChild( "name" ).getValue();

         String parameterDescription = parameter.getChild( "description" ).getValue();

         Xpp3Dom fieldConfigurationElement = configurationElement.getChild( parameterName );

         String parameterDefaultValue = "";

         if ( fieldConfigurationElement != null && fieldConfigurationElement.getValue() != null )

         {

             parameterDefaultValue = " (Default: " + fieldConfigurationElement.getAttribute( "default-value" ) + ")";

         }

         append( sb, parameterName + parameterDefaultValue, 2 );

         Xpp3Dom deprecated = parameter.getChild( "deprecated" );

         if ( ( deprecated != null ) && StringUtils.isNotEmpty( deprecated.getValue() ) )

         {

             append( sb, "Deprecated. " + deprecated.getValue(), 3 );

             append( sb, "", 0 );

         }

         append( sb, parameterDescription, 3 );

         if ( "true".equals( parameter.getChild( "required" ).getValue() ) )

         {

             append( sb, "Required: Yes", 3 );

         }

         Xpp3Dom expression = parameter.getChild( "expression" );

         if ( ( expression != null ) && StringUtils.isNotEmpty( expression.getValue() ) )

         {

             append( sb, "Expression: " + expression.getValue(), 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;

     }

 }