maven-compat/src/main/java/org/apache/maven/usability/plugin/ExpressionDocumenter.java

package org.apache.maven.usability.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 org.apache.maven.usability.plugin.io.xpp3.ParamdocXpp3Reader;
import org.codehaus.plexus.util.ReaderFactory;
import org.codehaus.plexus.util.xml.pull.XmlPullParserException;

import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * ExpressionDocumenter
 */
public class ExpressionDocumenter
{

    private static final String[] EXPRESSION_ROOTS =
    {
        "project", "settings", "session", "plugin", "rootless"
    };

    private static final String EXPRESSION_DOCO_ROOTPATH = "META-INF/maven/plugin-expressions/";

    private static Map<String, Expression> expressionDocumentation;

    public static Map<String, Expression> load()
        throws ExpressionDocumentationException
    {
        if ( expressionDocumentation == null )
        {
            expressionDocumentation = new HashMap<>();

            ClassLoader docLoader = initializeDocLoader();

            for ( String root : EXPRESSION_ROOTS )
            {
                try ( InputStream docStream = docLoader.getResourceAsStream(
                    EXPRESSION_DOCO_ROOTPATH + root + ".paramdoc.xml" ) )
                {
                    if ( docStream != null )
                    {
                        Map<String, Expression> doco = parseExpressionDocumentation( docStream );

                        expressionDocumentation.putAll( doco );
                    }
                }
                catch ( IOException e )
                {
                    throw new ExpressionDocumentationException(
                        "Failed to read documentation for expression root: " + root, e );
                }
                catch ( XmlPullParserException e )
                {
                    throw new ExpressionDocumentationException(
                        "Failed to parse documentation for expression root: " + root, e );
                }

            }
        }

        return expressionDocumentation;
    }

    /**
     * <expressions>
     * <expression>
     * <syntax>project.distributionManagementArtifactRepository</syntax>
     * <origin><![CDATA[
     * <distributionManagement>
     * <repository>
     * <id>some-repo</id>
     * <url>scp://host/path</url>
     * </repository>
     * <snapshotRepository>
     * <id>some-snap-repo</id>
     * <url>scp://host/snapshot-path</url>
     * </snapshotRepository>
     * </distributionManagement>
     * ]]></origin>
     * <usage><![CDATA[
     * The repositories onto which artifacts should be deployed.
     * One is for releases, the other for snapshots.
     * ]]></usage>
     * </expression>
     * <expressions>
     *
     * @throws IOException
     * @throws XmlPullParserException
     */
    private static Map<String, Expression> parseExpressionDocumentation( InputStream docStream )
        throws IOException, XmlPullParserException
    {
        Reader reader = new BufferedReader( ReaderFactory.newXmlReader( docStream ) );

        ParamdocXpp3Reader paramdocReader = new ParamdocXpp3Reader();

        ExpressionDocumentation documentation = paramdocReader.read( reader, true );

        List<Expression> expressions = documentation.getExpressions();

        Map<String, Expression> bySyntax = new HashMap<>();

        if ( expressions != null && !expressions.isEmpty() )
        {
            for ( Expression expression : expressions )
            {
                bySyntax.put( expression.getSyntax(), expression );
            }
        }

        return bySyntax;
    }

    private static ClassLoader initializeDocLoader()
        throws ExpressionDocumentationException
    {
        String myResourcePath = ExpressionDocumenter.class.getName().replace( '.', '/' ) + ".class";

        URL myResource = ExpressionDocumenter.class.getClassLoader().getResource( myResourcePath );

        assert myResource != null : "The resource is this class itself loaded by its own classloader and must exist";

        String myClasspathEntry = myResource.getPath();

        myClasspathEntry = myClasspathEntry.substring( 0, myClasspathEntry.length() - ( myResourcePath.length() + 2 ) );

        if ( myClasspathEntry.startsWith( "file:" ) )
        {
            myClasspathEntry = myClasspathEntry.substring( "file:".length() );
        }

        URL docResource;
        try
        {
            docResource = new File( myClasspathEntry ).toURL();
        }
        catch ( MalformedURLException e )
        {
            throw new ExpressionDocumentationException(
                "Cannot construct expression documentation classpath" + " resource base.", e );
        }

        return new URLClassLoader( new URL[]
        {
            docResource
        } );
    }

}