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/*
 * Copyright (c) 2010-2024 Sonatype, Inc.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *   Stuart McCulloch (Sonatype, Inc.) - initial API and implementation
 */
package org.eclipse.sisu.space;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.NoSuchElementException;
import java.util.Set;

import org.eclipse.sisu.inject.Logs;

/**
 * {@link ClassFinder} that finds {@link Class} resources listed in the named index.
 */
public final class IndexedClassFinder
    implements ClassFinder
{
    // ----------------------------------------------------------------------
    // Implementation fields
    // ----------------------------------------------------------------------

    private final String localPath;

    private final String indexName;

    // ----------------------------------------------------------------------
    // Constructors
    // ----------------------------------------------------------------------

    public IndexedClassFinder( final String name, final boolean global )
    {
        if ( global )
        {
            localPath = null;
            indexName = name;
        }
        else
        {
            final int i = name.lastIndexOf( '/' ) + 1;
            localPath = name.substring( 0, i );
            indexName = name.substring( i );
        }
    }

    // ----------------------------------------------------------------------
    // Public methods
    // ----------------------------------------------------------------------

    public Iterable indexedNames( final ClassSpace space )
    {
        final Enumeration indices;

        if ( null == localPath )
        {
            indices = space.getResources( indexName );
        }
        else
        {
            indices = space.findEntries( localPath, indexName, false );
        }

        final Set names = new LinkedHashSet();
        while ( indices.hasMoreElements() )
        {
            final URL url = indices.nextElement();
            try
            {
                final BufferedReader reader =
                    new BufferedReader( new InputStreamReader( Streams.open( url ), "UTF-8" ) );
                try
                {
                    // each index contains a list of class names, one per line with optional comment
                    for ( String line = reader.readLine(); line != null; line = reader.readLine() )
                    {
                        final int i = line.indexOf( '#' );
                        if ( i == 0 )
                        {
                            continue; // entire line is a comment, ignore it
                        }
                        final String name = ( i < 0 ? line : line.substring( 0, i ) ).trim();
                        if ( !name.isEmpty() )
                        {
                            names.add( name );
                        }
                    }
                }
                finally
                {
                    reader.close();
                }
            }
            catch ( final IOException e )
            {
                Logs.warn( "Problem reading: {}", url, e );
            }
        }
        return names;
    }

    public Enumeration findClasses( final ClassSpace space )
    {
        final Iterator itr = indexedNames( space ).iterator();

        return new Enumeration()
        {
            private URL nextURL;

            public boolean hasMoreElements()
            {
                while ( null == nextURL && itr.hasNext() )
                {
                    nextURL = space.getResource( itr.next().replace( '.', '/' ) + ".class" );
                }
                return null != nextURL;
            }

            public URL nextElement()
            {
                if ( hasMoreElements() )
                {
                    final URL tempURL = nextURL;
                    nextURL = null;
                    return tempURL;
                }
                throw new NoSuchElementException();
            }
        };
    }
}