/*
    * 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
    *
    *     https://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.commons.configuration2.tree;
  
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.Map.Entry;
  import java.util.stream.Collectors;
  
  /**
   * An internally used helper class for storing information about the managed node structure. An instance of this class
   * represents the current tree. It stores the current root node and additional information which is not part of the
   * {@code ImmutableNode} class.
   *
   * @since 2.0
   */
  final class TreeData extends AbstractImmutableNodeHandler implements ReferenceNodeHandler {
  
      /**
       * Checks whether the passed in node is subject of a replacement by another one. If so, the other node is returned. This
       * is done until a node is found which had not been replaced. Updating the parent mapping may be expensive for large
       * node structures. Therefore, it initially remains constant, and a map with replacements is used. When querying a
       * parent node, the replacement map has to be consulted whether the parent node is still valid.
       *
       * @param replace the replacement node
       * @param mapping the replacement mapping
       * @return the corresponding node according to the mapping
       */
      private static ImmutableNode handleReplacements(final ImmutableNode replace, final Map<ImmutableNode, ImmutableNode> mapping) {
          ImmutableNode node = replace;
          ImmutableNode org;
          do {
              org = mapping.get(node);
              if (org != null) {
                  node = org;
              }
          } while (org != null);
          return node;
      }
  
      /** The root node of the tree. */
      private final ImmutableNode root;
  
      /** A map that associates the parent node to each node. */
      private final Map<ImmutableNode, ImmutableNode> parentMapping;
  
      /**
       * Stores information about nodes which have been replaced by manipulations of the structure. This map is used to avoid
       * that the parent mapping has to be updated after each change.
       */
      private final Map<ImmutableNode, ImmutableNode> replacementMapping;
  
      /** An inverse replacement mapping. */
      private final Map<ImmutableNode, ImmutableNode> inverseReplacementMapping;
  
      /** The node tracker. */
      private final NodeTracker nodeTracker;
  
      /** The reference tracker. */
      private final ReferenceTracker referenceTracker;
  
      /**
       * Creates a new instance of {@code TreeData} and initializes it with all data to be stored.
       *
       * @param root the root node of the current tree
       * @param parentMapping the mapping to parent nodes
       * @param replacements the map with the nodes that have been replaced
       * @param tracker the {@code NodeTracker}
       * @param refTracker the {@code ReferenceTracker}
       */
      public TreeData(final ImmutableNode root, final Map<ImmutableNode, ImmutableNode> parentMapping, final Map<ImmutableNode, ImmutableNode> replacements,
          final NodeTracker tracker, final ReferenceTracker refTracker) {
          this.root = root;
          this.parentMapping = parentMapping;
          replacementMapping = replacements;
          inverseReplacementMapping = createInverseMapping(replacements);
          nodeTracker = tracker;
          referenceTracker = refTracker;
      }
  
      /**
       * Returns a copy of the mapping from nodes to their parents.
       *
       * @return the copy of the parent mapping
      */
     public Map<ImmutableNode, ImmutableNode> copyParentMapping() {
         return new HashMap<>(parentMapping);
     }
 
     /**
      * Returns a copy of the map storing the replaced nodes.
      *
      * @return the copy of the replacement mapping
      */
     public Map<ImmutableNode, ImmutableNode> copyReplacementMapping() {
         return new HashMap<>(replacementMapping);
     }
 
     /**
      * Creates the inverse replacement mapping.
      *
      * @param replacements the original replacement mapping
      * @return the inverse replacement mapping
      */
     private Map<ImmutableNode, ImmutableNode> createInverseMapping(final Map<ImmutableNode, ImmutableNode> replacements) {
         return replacements.entrySet().stream().collect(Collectors.toMap(Entry::getValue, Entry::getKey));
     }
 
     /**
      * Gets the {@code NodeTracker}
      *
      * @return the {@code NodeTracker}
      */
     public NodeTracker getNodeTracker() {
         return nodeTracker;
     }
 
     /**
      * Gets the parent node of the specified node. Result is <strong>null</strong> for the root node. If the passed in node cannot
      * be resolved, an exception is thrown.
      *
      * @param node the node in question
      * @return the parent node for this node
      * @throws IllegalArgumentException if the node cannot be resolved
      */
     @Override
     public ImmutableNode getParent(final ImmutableNode node) {
         if (node == getRootNode()) {
             return null;
         }
         final ImmutableNode org = handleReplacements(node, inverseReplacementMapping);
 
         final ImmutableNode parent = parentMapping.get(org);
         if (parent == null) {
             throw new IllegalArgumentException("Cannot determine parent! " + node + " is not part of this model.");
         }
         return handleReplacements(parent, replacementMapping);
     }
 
     /**
      * {@inheritDoc} This implementation delegates to the reference tracker.
      */
     @Override
     public Object getReference(final ImmutableNode node) {
         return getReferenceTracker().getReference(node);
     }
 
     /**
      * Gets the {@code ReferenceTracker}.
      *
      * @return the {@code ReferenceTracker}
      */
     public ReferenceTracker getReferenceTracker() {
         return referenceTracker;
     }
 
     @Override
     public ImmutableNode getRootNode() {
         return root;
     }
 
     /**
      * {@inheritDoc} This implementation delegates to the reference tracker.
      */
     @Override
     public List<Object> removedReferences() {
         return getReferenceTracker().getRemovedReferences();
     }
 
     /**
      * Creates a new instance which uses the specified {@code NodeTracker}. This method is called when there are updates of
      * the state of tracked nodes.
      *
      * @param newTracker the new {@code NodeTracker}
      * @return the updated instance
      */
     public TreeData updateNodeTracker(final NodeTracker newTracker) {
         return new TreeData(root, parentMapping, replacementMapping, newTracker, referenceTracker);
     }
 
     /**
      * Creates a new instance which uses the specified {@code ReferenceTracker}. All other information are unchanged. This
      * method is called when there updates for references.
      *
      * @param newTracker the new {@code ReferenceTracker}
      * @return the updated instance
      */
     public TreeData updateReferenceTracker(final ReferenceTracker newTracker) {
         return new TreeData(root, parentMapping, replacementMapping, nodeTracker, newTracker);
     }
 }