/*
    * 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.
   */
  package org.eclipse.aether.util.repository;
  
  import java.io.File;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.LinkedHashSet;
  import java.util.List;
  import java.util.Objects;
  import java.util.concurrent.atomic.AtomicReference;
  
  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;
      private final AtomicReference<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) {
          ArrayList<WorkspaceReader> list = new ArrayList<>();
          if (readers != null) {
              Arrays.stream(readers).filter(Objects::nonNull).forEach(list::add);
          }
          StringBuilder buffer = new StringBuilder();
          for (WorkspaceReader reader : list) {
              if (buffer.length() > 0) {
                  buffer.append('+');
              }
              buffer.append(reader.getRepository().getContentType());
          }
          this.readers = Collections.unmodifiableList(list);
          this.repository = new AtomicReference<>(new WorkspaceRepository(buffer.toString(), new Key(list)));
      }
  
      /**
       * 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);
      }
  
      @Override
      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;
      }
  
      @Override
      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));
     }
 
     @Override
     public WorkspaceRepository getRepository() {
         Key key = new Key(readers);
         return repository.updateAndGet(r -> {
             if (!key.equals(r.getKey())) {
                 return new WorkspaceRepository(r.getContentType(), key);
             } else {
                 return r;
             }
         });
     }
 
     private static class Key {
         private final List<Object> keys;
 
         Key(List<WorkspaceReader> readers) {
             ArrayList<Object> keys = new ArrayList<>();
             for (WorkspaceReader reader : readers) {
                 keys.add(reader.getRepository().getKey());
             }
             this.keys = keys;
         }
 
         @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();
         }
     }
 }