package org.apache.maven.doxia.linkcheck.validation;

/*
 * 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.File;
import java.io.IOException;
import java.io.Reader;
import java.util.Locale;

import org.apache.maven.doxia.linkcheck.model.LinkcheckFileResult;
import org.codehaus.plexus.util.IOUtil;
import org.codehaus.plexus.util.ReaderFactory;
import org.codehaus.plexus.util.StringUtils;
import org.codehaus.plexus.util.WriterFactory;

/**
 * A link validator solely for files on the local filesystem.
 *
 * @author <a href="mailto:bwalding@apache.org">Ben Walding</a>
 * @author <a href="mailto:aheritier@apache.org">Arnaud Heritier</a>
 */
public final class FileLinkValidator
    implements LinkValidator
{
    private String encoding;

    /**
     * @param encoding the encoding file used. If empty, using UTF-8.
     */
    public FileLinkValidator( String encoding )
    {
        if ( StringUtils.isEmpty( encoding ) )
        {
            encoding = WriterFactory.UTF_8;
        }
        this.encoding = encoding;
    }

    /** {@inheritDoc} */
    @Override
    public LinkValidationResult validateLink( LinkValidationItem lvi )
    {
        File f = getFile( lvi );

        if ( f.exists() )
        {
            return new LinkValidationResult( LinkcheckFileResult.VALID_LEVEL, false, "" );
        }

        return new LinkValidationResult( LinkcheckFileResult.ERROR_LEVEL, false, "doesn't exist." );
    }

    /** {@inheritDoc} */
    @Override
    public Object getResourceKey( LinkValidationItem lvi )
    {
        String link = lvi.getLink();

        // If we find an http(s) link or a mail link, it's not good
        // links starting with "/" should have a base URL pre-pended and be handled by OnlineHTTPLinkValidator.
        if ( link.toLowerCase( Locale.ENGLISH ).startsWith( "http://" )
            || link.toLowerCase( Locale.ENGLISH ).startsWith( "https://" ) || link.indexOf( '@' ) != -1
            || link.startsWith( "/" ) )
        {
            return null;
        }

        return getFile( lvi ).getAbsolutePath();
    }

    // ----------------------------------------------------------------------
    // Private methods
    // ----------------------------------------------------------------------

    /**
     * Returns the link of the given LinkValidationItem as a File.
     *
     * @param lvi The LinkValidationItem.
     * @return File the link as a File.
     */
    private File getFile( LinkValidationItem lvi )
    {
        String link = lvi.getLink();

        if ( link.indexOf( '#' ) != -1 )
        {
            String anchor = link.substring( link.indexOf( '#' ) + 1 );
            link = link.substring( 0, link.indexOf( '#' ) );

            // If the link was just #fred or similar, then the file is the file it came from
            if ( link.trim().length() == 0 ) // in the same file
            {
                // the anchor exists?
                String content = read( lvi.getSource(), encoding );
                if ( Anchors.matchesAnchor( content, anchor ) )
                {
                    return lvi.getSource();
                }

                // return an invalid file
                return new File( lvi.getLink() );
            }

            // the anchor exists?
            String content = read( new File( lvi.getSource().getParentFile(), link ), encoding );
            if ( Anchors.matchesAnchor( content, anchor ) )
            {
                return new File( lvi.getSource().getParentFile(), link );
            }

            // return an invalid file
            return new File( lvi.getLink() );
        }

        if ( link.indexOf( '?' ) != -1 )
        {
            link = link.substring( 0, link.indexOf( '?' ) );

            // If the link was just ?param=something or similar, then the file is the file it came from
            // XXX: Theoretically we could even validate the anchor tag?
            if ( link.trim().length() == 0 )
            {
                return lvi.getSource();
            }
        }

        return new File( lvi.getSource().getParentFile(), link );
    }

    /**
     * @param f not null
     * @param encoding the encoding file used
     * @return the content of the file or null if an error occurred.
     */
    private static String read( File f, String encoding )
    {
        try ( Reader reader = ReaderFactory.newReader( f, encoding ) )
        {
            return IOUtil.toString( reader );
        }
        catch ( IOException e )
        {
            // nop;
        }

        return null;
    }
}