package org.eclipse.aether.util.repository;
   
   /*
    * 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.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;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * A workspace reader that delegates to a chain of other readers, effectively aggregating their contents.
   */
  public final class ChainedWorkspaceReader
      implements WorkspaceReader
  {
  
      private final List<WorkspaceReader> 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 )
      {
          requireNonNull( artifact, "artifact cannot be null" );
          File file = null;
  
          for ( WorkspaceReader reader : readers )
          {
             file = reader.findArtifact( artifact );
             if ( file != null )
             {
                 break;
             }
         }
 
         return file;
     }
 
     public List<String> findVersions( Artifact artifact )
     {
         requireNonNull( artifact, "artifact cannot be null" );
         Collection<String> 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<Object> keys = new ArrayList<>();
 
         Key( List<WorkspaceReader> readers )
         {
             for ( WorkspaceReader reader : readers )
             {
                 keys.add( reader.getRepository().getKey() );
             }
         }
 
         @Override
         public boolean equals( Object obj )
         {
             if ( this == obj )
             {
                 return true;
             }
             if ( obj == null || !getClass().equals( obj.getClass() ) )
             {
                 return false;
             }
             return keys.equals( ( (Key) obj ).keys );
         }
 
         @Override
         public int hashCode()
         {
             return keys.hashCode();
         }
 
     }
 
 }