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/*******************************************************************************
 * Copyright (c) 2010, 2013 Sonatype, Inc.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    Sonatype, Inc. - initial API and implementation
 *******************************************************************************/
package org.eclipse.aether.util.repository;

import java.io.File;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.List;

import org.eclipse.aether.artifact.Artifact;
import org.eclipse.aether.repository.WorkspaceReader;
import org.eclipse.aether.repository.WorkspaceRepository;

/**
 * A workspace reader that delegates to a chain of other readers, effectively aggregating their contents.
 */
public final class ChainedWorkspaceReader
    implements WorkspaceReader
{

    private List readers = new ArrayList();

    private WorkspaceRepository repository;

    /**
     * Creates a new workspace reader by chaining the specified readers.
     * 
     * @param readers The readers to chain, may be {@code null}.
     * @see #newInstance(WorkspaceReader, WorkspaceReader)
     */
    public ChainedWorkspaceReader( WorkspaceReader... readers )
    {
        if ( readers != null )
        {
            Collections.addAll( this.readers, readers );
        }

        StringBuilder buffer = new StringBuilder();
        for ( WorkspaceReader reader : this.readers )
        {
            if ( buffer.length() > 0 )
            {
                buffer.append( '+' );
            }
            buffer.append( reader.getRepository().getContentType() );
        }

        repository = new WorkspaceRepository( buffer.toString(), new Key( this.readers ) );
    }

    /**
     * Creates a new workspace reader by chaining the specified readers. In contrast to the constructor, this factory
     * method will avoid creating an actual chained reader if one of the specified readers is actually {@code null}.
     * 
     * @param reader1 The first workspace reader, may be {@code null}.
     * @param reader2 The second workspace reader, may be {@code null}.
     * @return The chained reader or {@code null} if no workspace reader was supplied.
     */
    public static WorkspaceReader newInstance( WorkspaceReader reader1, WorkspaceReader reader2 )
    {
        if ( reader1 == null )
        {
            return reader2;
        }
        else if ( reader2 == null )
        {
            return reader1;
        }
        return new ChainedWorkspaceReader( reader1, reader2 );
    }

    public File findArtifact( Artifact artifact )
    {
        File file = null;

        for ( WorkspaceReader reader : readers )
        {
            file = reader.findArtifact( artifact );
            if ( file != null )
            {
                break;
            }
        }

        return file;
    }

    public List findVersions( Artifact artifact )
    {
        Collection versions = new LinkedHashSet();

        for ( WorkspaceReader reader : readers )
        {
            versions.addAll( reader.findVersions( artifact ) );
        }

        return Collections.unmodifiableList( new ArrayList( versions ) );
    }

    public WorkspaceRepository getRepository()
    {
        Key key = new Key( readers );
        if ( !key.equals( repository.getKey() ) )
        {
            repository = new WorkspaceRepository( repository.getContentType(), key );
        }
        return repository;
    }

    private static class Key
    {

        private final List