/*
    * 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.apache.maven.resolver;
  
  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.stream.Collectors;
  
  import org.apache.maven.api.model.Model;
  import org.apache.maven.internal.impl.resolver.MavenWorkspaceReader;
  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 maven workspace reader that delegates to a chain of other readers, effectively aggregating their contents.
   * <p>
   * This class, while technically is not immutable, should be considered as such once set up. If not mutated, it is also
   * thread-safe. <em>The mutation of this class instances should happen beforehand their use in session</em>.
   */
  public class MavenChainedWorkspaceReader implements MavenWorkspaceReader {
  
      protected List<WorkspaceReader> readers;
      protected WorkspaceRepository repository;
  
      /**
       * Creates a new workspace reader by chaining the specified readers.
       *
       * @param readers The readers to chain must not be {@code null}.
       */
      public MavenChainedWorkspaceReader(WorkspaceReader... readers) {
          setReaders(Arrays.asList(readers));
      }
  
      @Override
      public WorkspaceRepository getRepository() {
          return this.repository;
      }
  
      @Override
      public Model findModel(Artifact artifact) {
          requireNonNull(artifact, "artifact cannot be null");
          Model model = null;
  
          for (WorkspaceReader workspaceReader : readers) {
              if (workspaceReader instanceof MavenWorkspaceReader) {
                  model = ((MavenWorkspaceReader) workspaceReader).findModel(artifact);
                  if (model != null) {
                      break;
                  }
              }
          }
  
          return model;
      }
  
      @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));
     }
 
     public void setReaders(Collection<WorkspaceReader> readers) {
         requireNonNull(readers, "readers");
         // skip possible null entries
         this.readers = Collections.unmodifiableList(
                 new ArrayList<>(readers.stream().filter(Objects::nonNull).collect(Collectors.toList())));
         Key key = new Key(this.readers);
         this.repository = new WorkspaceRepository(key.getContentType(), key);
     }
 
     public List<WorkspaceReader> getReaders() {
         return readers;
     }
 
     public void addReader(WorkspaceReader workspaceReader) {
         requireNonNull(workspaceReader, "workspaceReader");
         ArrayList<WorkspaceReader> newReaders = new ArrayList<>(this.readers);
         newReaders.add(workspaceReader);
         setReaders(newReaders);
     }
 
     private static class Key {
         private final List<Object> keys;
         private final String type;
 
         Key(Collection<WorkspaceReader> readers) {
             keys = readers.stream().map(r -> r.getRepository().getKey()).collect(Collectors.toList());
             type = readers.stream().map(r -> r.getRepository().getContentType()).collect(Collectors.joining("+"));
         }
 
         public String getContentType() {
             return type;
         }
 
         public boolean equals(Object obj) {
             if (this == obj) {
                 return true;
             } else {
                 return obj != null && this.getClass().equals(obj.getClass()) && this.keys.equals(((Key) obj).keys);
             }
         }
 
         public int hashCode() {
             return this.keys.hashCode();
         }
     }
 
     /**
      * chains a collection of {@link WorkspaceReader}s
      * @param workspaceReaderCollection the collection of readers, might be empty but never <code>null</code>
      * @return if the collection contains only one item returns the single item, otherwise creates a new
      *         {@link MavenChainedWorkspaceReader} chaining all readers in the order of the given collection.
      */
     public static WorkspaceReader of(Collection<WorkspaceReader> workspaceReaderCollection) {
         WorkspaceReader[] readers = workspaceReaderCollection.toArray(new WorkspaceReader[0]);
         if (readers.length == 1) {
             return readers[0];
         }
         return new MavenChainedWorkspaceReader(readers);
     }
 }