/*
    * 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.graph.traverser;
  
  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);
      }
  
      @Override
      public boolean traverseDependency(Dependency dependency) {
          requireNonNull(dependency, "dependency cannot be null");
          for (DependencyTraverser traverser : traversers) {
              if (!traverser.traverseDependency(dependency)) {
                 return false;
             }
         }
         return true;
     }
 
     @Override
     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;
     }
 }