package org.eclipse.aether.util.graph.traverser;
   
   /*
    * 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.util.Arrays;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.LinkedHashSet;
  import java.util.Set;
  
  import org.eclipse.aether.collection.DependencyCollectionContext;
  import org.eclipse.aether.collection.DependencyTraverser;
  import org.eclipse.aether.graph.Dependency;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * A dependency traverser that combines zero or more other traversers using a logical {@code AND}. The resulting
   * traverser enables processing of child dependencies if and only if all constituent traversers request traversal.
   */
  public final class AndDependencyTraverser
      implements DependencyTraverser
  {
  
      private final Set<? extends DependencyTraverser> traversers;
  
      private int hashCode;
  
      /**
       * Creates a new traverser from the specified traversers. Prefer
       * {@link #newInstance(DependencyTraverser, DependencyTraverser)} if any of the input traversers might be
       * {@code null}.
       * 
       * @param traversers The traversers to combine, may be {@code null} but must not contain {@code null} elements.
       */
      public AndDependencyTraverser( DependencyTraverser... traversers )
      {
          if ( traversers != null && traversers.length > 0 )
          {
              this.traversers = new LinkedHashSet<>( Arrays.asList( traversers ) );
          }
          else
          {
              this.traversers = Collections.emptySet();
          }
      }
  
      /**
       * Creates a new traverser from the specified traversers.
       * 
       * @param traversers The traversers to combine, may be {@code null} but must not contain {@code null} elements.
       */
      public AndDependencyTraverser( Collection<? extends DependencyTraverser> traversers )
      {
          if ( traversers != null && !traversers.isEmpty() )
          {
              this.traversers = new LinkedHashSet<>( traversers );
          }
          else
          {
              this.traversers = Collections.emptySet();
          }
      }
  
      private AndDependencyTraverser( Set<DependencyTraverser> traversers )
      {
          if ( traversers != null && !traversers.isEmpty() )
          {
              this.traversers = traversers;
          }
          else
          {
              this.traversers = Collections.emptySet();
          }
      }
  
      /**
       * Creates a new traverser from the specified traversers.
       * 
       * @param traverser1 The first traverser to combine, may be {@code null}.
       * @param traverser2 The second traverser to combine, may be {@code null}.
       * @return The combined traverser or {@code null} if both traversers were {@code null}.
      */
     public static DependencyTraverser newInstance( DependencyTraverser traverser1, DependencyTraverser traverser2 )
     {
         if ( traverser1 == null )
         {
             return traverser2;
         }
         else if ( traverser2 == null || traverser2.equals( traverser1 ) )
         {
             return traverser1;
         }
         return new AndDependencyTraverser( traverser1, traverser2 );
     }
 
     public boolean traverseDependency( Dependency dependency )
     {
         requireNonNull( dependency, "dependency cannot be null" );
         for ( DependencyTraverser traverser : traversers )
         {
             if ( !traverser.traverseDependency( dependency ) )
             {
                 return false;
             }
         }
         return true;
     }
 
     public DependencyTraverser deriveChildTraverser( DependencyCollectionContext context )
     {
         requireNonNull( context, "context cannot be null" );
         int seen = 0;
         Set<DependencyTraverser> childTraversers = null;
 
         for ( DependencyTraverser traverser : traversers )
         {
             DependencyTraverser childTraverser = traverser.deriveChildTraverser( context );
             if ( childTraversers != null )
             {
                 if ( childTraverser != null )
                 {
                     childTraversers.add( childTraverser );
                 }
             }
             else if ( traverser != childTraverser )
             {
                 childTraversers = new LinkedHashSet<>();
                 if ( seen > 0 )
                 {
                     for ( DependencyTraverser s : traversers )
                     {
                         if ( childTraversers.size() >= seen )
                         {
                             break;
                         }
                         childTraversers.add( s );
                     }
                 }
                 if ( childTraverser != null )
                 {
                     childTraversers.add( childTraverser );
                 }
             }
             else
             {
                 seen++;
             }
         }
 
         if ( childTraversers == null )
         {
             return this;
         }
         if ( childTraversers.size() <= 1 )
         {
             if ( childTraversers.isEmpty() )
             {
                 return null;
             }
             return childTraversers.iterator().next();
         }
         return new AndDependencyTraverser( childTraversers );
     }
 
     @Override
     public boolean equals( Object obj )
     {
         if ( this == obj )
         {
             return true;
         }
         else if ( null == obj || !getClass().equals( obj.getClass() ) )
         {
             return false;
         }
 
         AndDependencyTraverser that = (AndDependencyTraverser) obj;
         return traversers.equals( that.traversers );
     }
 
     @Override
     public int hashCode()
     {
         if ( hashCode == 0 )
         {
             int hash = 17;
             hash = hash * 31 + traversers.hashCode();
             hashCode = hash;
         }
         return hashCode;
     }
 
 }