src/main/java/org/apache/maven/shared/runtime/MavenRuntimeVisitorUtils.java

package org.apache.maven.shared.runtime;

/*
 * 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.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Set;
import java.util.jar.JarEntry;
import java.util.jar.JarInputStream;

import org.apache.maven.shared.utils.io.IOUtil;

/**
 * Provides various methods of applying Maven runtime visitors.
 * 
 * @author <a href="mailto:markh@apache.org">Mark Hobson</a>
 * @version $Id$
 * @see MavenRuntimeVisitor
 */
final class MavenRuntimeVisitorUtils
{
    // constants --------------------------------------------------------------

    /**
     * The path to Maven's metadata directory.
     */
    private static final String MAVEN_PATH = "META-INF/maven";

    /**
     * The path elements of a Maven project properties file, where {@code null} is a wildcard.
     */
    private static final String[] PROPERTIES_PATH_TOKENS =
        new String[] { "META-INF", "maven", null, null, "pom.properties" };

    /**
     * The path elements of a Maven project XML file, where {@code null} is a wildcard.
     */
    private static final String[] XML_PATH_TOKENS = new String[] { "META-INF", "maven", null, null, "pom.xml" };

    /**
     * The path element index of a Maven project properties/XML file that contains the project group id.
     */
    private static final int GROUP_ID_TOKEN_INDEX = 2;

    /**
     * The path element index of a Maven project properties/XML file that contains the project artifact id.
     */
    private static final int ARTIFACT_ID_TOKEN_INDEX = 3;

    // constructors -----------------------------------------------------------

    /**
     * {@code MavenRuntimeVisitorUtils} is not intended to be instantiated.
     */
    private MavenRuntimeVisitorUtils()
    {
        throw new AssertionError();
    }

    // public methods ---------------------------------------------------------

    /**
     * Invokes the specified visitor on all Maven projects found within the specified class loader.
     * 
     * @param classLoader
     *            the class loader to introspect
     * @param visitor
     *            the visitor to invoke
     * @throws MavenRuntimeException
     *             if an error occurs visiting the projects
     */
    public static void accept( ClassLoader classLoader, MavenRuntimeVisitor visitor )
        throws MavenRuntimeException
    {
        Enumeration<URL> urls;

        try
        {
            urls = classLoader.getResources( MAVEN_PATH );
        }
        catch ( IOException exception )
        {
            throw new MavenRuntimeException( "Cannot obtain Maven metadata from class loader: " + classLoader,
                                             exception );
        }

        Set<String> visitedProjectProperties = new HashSet<String>();
        Set<String> visitedProjectXML = new HashSet<String>();

        while ( urls.hasMoreElements() )
        {
            URL url = urls.nextElement();

            acceptURL( url, visitor, visitedProjectProperties, visitedProjectXML );
        }
    }

    /**
     * Invokes the specified visitor on the specified class's Maven project.
     * 
     * @param klass
     *            the class to introspect
     * @param visitor
     *            the visitor to invoke
     * @throws MavenRuntimeException
     *             if an error occurs visiting the projects
     */
    public static void accept( Class<?> klass, MavenRuntimeVisitor visitor )
        throws MavenRuntimeException
    {
        try
        {
            URL baseURL = ClassUtils.getBaseURL( klass );
            URL url = new URL( baseURL, MAVEN_PATH );

            acceptURL( url, visitor, new HashSet<String>(), new HashSet<String>() );
        }
        catch ( MalformedURLException exception )
        {
            throw new MavenRuntimeException( "Cannot obtain URL for class: " + klass.getName(), exception );
        }
    }

    /**
     * Invokes the specified visitor on the specified URL's Maven project.
     * 
     * @param url
     *            the URL to introspect
     * @param visitor
     *            the visitor to invoke
     * @throws MavenRuntimeException
     *             if an error occurs visiting the projects
     */
    public static void accept( URL url, MavenRuntimeVisitor visitor )
        throws MavenRuntimeException
    {
        try
        {
            if ( "jar".equals( url.getProtocol() ) )
            {
                url = getJarFileURL( url );
            }
            
            URL baseURL = getJarEntryURL( url, "" );
            URL mavenURL = new URL( baseURL, MAVEN_PATH );

            acceptURL( mavenURL, visitor, new HashSet<String>(), new HashSet<String>() );
        }
        catch ( MalformedURLException exception )
        {
            throw new MavenRuntimeException( "Cannot obtain URL for Jar: " + url, exception );
        }
    }

    // private methods --------------------------------------------------------

    /**
     * Invokes the specified visitor on all Maven projects found within the specified Maven metadata URL.
     * 
     * @param url
     *            the URL of the Maven metadata directory to introspect
     * @param visitor
     *            the visitor to invoke
     * @param visitedProjectProperties
     *            the ids of projects' properties that have been visited
     * @param visitedProjectXML
     *            the ids of projects' XML that have been visited
     * @throws MavenRuntimeException
     *             if an error occurs visiting the projects
     */
    private static void acceptURL( URL url, MavenRuntimeVisitor visitor, Set<String> visitedProjectProperties,
                                   Set<String> visitedProjectXML ) throws MavenRuntimeException
    {
        if ( "jar".equals( url.getProtocol() ) )
        {
            URL jarURL;

            try
            {
                jarURL = getJarFileURL( url );
            }
            catch ( MalformedURLException exception )
            {
                throw new MavenRuntimeException( "Cannot obtain Jar file URL for URL: " + url, exception );
            }

            acceptJar( jarURL, visitor, visitedProjectProperties, visitedProjectXML );
        }
    }

    /**
     * Invokes the specified visitor on all Maven projects found within the specified Jar URL.
     * 
     * @param url
     *            the Jar URL to introspect
     * @param visitor
     *            the visitor to invoke
     * @param visitedProjectProperties
     *            the ids of projects' properties that have been visited
     * @param visitedProjectXML
     *            the ids of projects' XML that have been visited
     * @throws MavenRuntimeException
     *             if an error occurs visiting the projects
     */
    private static void acceptJar( URL url, MavenRuntimeVisitor visitor, Set<String> visitedProjectProperties,
                                   Set<String> visitedProjectXML ) throws MavenRuntimeException
    {
        JarInputStream in = null;

        try
        {
            URLConnection connection = url.openConnection();
            connection.setUseCaches( false );

            in = new JarInputStream( connection.getInputStream() );

            JarEntry entry;

            while ( ( entry = in.getNextJarEntry() ) != null )
            {
                acceptJarEntry( url, entry, visitor, visitedProjectProperties, visitedProjectXML );
            }
        }
        catch ( IOException exception )
        {
            throw new MavenRuntimeException( "Cannot read jar", exception );
        }
        finally
        {
            IOUtil.close( in );
        }
    }

    /**
     * Invokes the specified visitor on the specified Jar entry if it corresponds to a Maven project XML or properties
     * file.
     * 
     * @param jarURL
     *            a URL to the Jar file for this entry
     * @param entry
     *            the Jar entry to introspect
     * @param visitor
     *            the visitor to invoke
     * @param visitedProjectProperties
     *            the ids of projects' properties that have been visited
     * @param visitedProjectXML
     *            the ids of projects' XML that have been visited
     * @throws MavenRuntimeException
     *             if an error occurs visiting the projects
     */
    private static void acceptJarEntry( URL jarURL, JarEntry entry, MavenRuntimeVisitor visitor,
                                        Set<String> visitedProjectProperties, Set<String> visitedProjectXML )
        throws MavenRuntimeException
    {
        String name = entry.getName();

        try
        {
            URL url = getJarEntryURL( jarURL, entry.getName() );

            if ( isProjectPropertiesPath( name ) )
            {
                String projectId = getProjectId( name );

                if ( !visitedProjectProperties.contains( projectId ) )
                {
                    visitor.visitProjectProperties( url );

                    visitedProjectProperties.add( projectId );
                }
            }
            else if ( isProjectXMLPath( name ) )
            {
                String projectId = getProjectId( name );

                if ( !visitedProjectXML.contains( projectId ) )
                {
                    visitor.visitProjectXML( url );

                    visitedProjectXML.add( projectId );
                }
            }
        }
        catch ( MalformedURLException exception )
        {
            throw new MavenRuntimeException( "Cannot read jar entry", exception );
        }
    }

    /**
     * Gets the underlying Jar file URL for the specified Jar entry URL.
     * 
     * @param url
     *            the Jar entry URL
     * @return the Jar file URL
     * @throws MalformedURLException
     *             if an error occurs deriving the Jar file URL
     */
    private static URL getJarFileURL( URL url ) throws MalformedURLException
    {
        if ( !"jar".equals( url.getProtocol() ) )
        {
            return url;
        }

        String path = url.getPath();

        int index = path.indexOf( "!/" );

        if ( index != -1 )
        {
            path = path.substring( 0, index );
        }

        return new URL( path );
    }
    
    private static URL getJarEntryURL( URL jarURL, String entryName ) throws MalformedURLException
    {
        return new URL( "jar:" + jarURL + "!/" + entryName );
    }

    /**
     * Gets a unique project identifier for the specified Maven project properties/XML file.
     * 
     * @param path
     *            the path to a Maven project properties/XML file
     * @return the unique project identifier
     */
    private static String getProjectId( String path )
    {
        String[] tokens = path.split( "/" );

        String groupId = tokens[GROUP_ID_TOKEN_INDEX];
        String artifactId = tokens[ARTIFACT_ID_TOKEN_INDEX];

        return groupId + ":" + artifactId;
    }

    /**
     * Gets whether the specified path represents a Maven project properties file.
     * 
     * @param path
     *            the path to examine
     * @return {@code true} if the specified path represents a Maven project properties file
     */
    private static boolean isProjectPropertiesPath( String path )
    {
        return matches( PROPERTIES_PATH_TOKENS, path.split( "/" ) );
    }

    /**
     * Gets whether the specified path represents a Maven project XML file.
     * 
     * @param path
     *            the path to examine
     * @return {@code true} if the specified path represents a Maven project XML file
     */
    private static boolean isProjectXMLPath( String path )
    {
        return matches( XML_PATH_TOKENS, path.split( "/" ) );
    }

    /**
     * Gets whether the specified string arrays are equal, with wildcard support.
     * 
     * @param matchTokens
     *            the string tokens to match, where {@code null} represents a wildcard
     * @param tokens
     *            the string tokens to test
     * @return {@code true} if the {@code tokens} array equals the {@code matchTokens}, treating any {@code null}
     *         {@code matchTokens} values as wildcards
     */
    private static boolean matches( String[] matchTokens, String[] tokens )
    {
        if ( tokens.length != matchTokens.length )
        {
            return false;
        }

        for ( int i = 0; i < tokens.length; i++ )
        {
            if ( matchTokens[i] != null && !tokens[i].equals( matchTokens[i] ) )
            {
                return false;
            }
        }

        return true;
    }
}