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.IOUtil;
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;

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 expressionDocumentation;

    public static Map load()
        throws ExpressionDocumentationException
    {
        if ( expressionDocumentation == null )
        {
            expressionDocumentation = new HashMap();

            ClassLoader docLoader = initializeDocLoader();

            for ( String EXPRESSION_ROOT : EXPRESSION_ROOTS )
            {
                InputStream docStream = null;
                try
                {
                    docStream =
                        docLoader.getResourceAsStream( EXPRESSION_DOCO_ROOTPATH + EXPRESSION_ROOT + ".paramdoc.xml" );

                    if ( docStream != null )
                    {
                        Map doco = parseExpressionDocumentation( docStream );

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

        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 parseExpressionDocumentation( InputStream docStream )
        throws IOException, XmlPullParserException
    {
        Reader reader = new BufferedReader( ReaderFactory.newXmlReader( docStream ) );

        ParamdocXpp3Reader paramdocReader = new ParamdocXpp3Reader();

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

        List expressions = documentation.getExpressions();

        Map bySyntax = new HashMap();

        if ( expressions != null && !expressions.isEmpty() )
        {
            for ( Object expression : expressions )
            {
                Expression expr = (Expression) expression;

                bySyntax.put( expr.getSyntax(), expr );
            }
        }

        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 } );
    }

}