/*
    * 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.Collection;
  import java.util.List;
  import java.util.concurrent.atomic.AtomicBoolean;
  
  /**
   * <p>
   * A specialized {@code NodeModel} implementation that uses a tracked node managed by an {@link InMemoryNodeModel}
   * object as root node.
   * </p>
   * <p>
   * Models of this type are useful when working on specific sub trees of a nodes structure. This is the case for instance
   * for a {@code SubnodeConfiguration}.
   * </p>
   * <p>
   * An instance of this class is constructed with an {@link InMemoryNodeModelSupport} object providing a reference to the
   * underlying {@code InMemoryNodeModel} and the {@link NodeSelector} pointing to the tracked node acting as this model's
   * root node. The {@code NodeModel} operations are implemented by delegating to the wrapped {@code InMemoryNodeModel}
   * object specifying the selector to the tracked node as target root node for the update transaction. Note that the
   * tracked node can become detached at any time. This situation is handled transparently by the implementation of
   * {@code InMemoryNodeModel}. The reason for using an {@code InMemoryNodeModelSupport} object rather than an
   * {@code InMemoryNodeModel} directly is that this additional layer of indirection can be used for performing special
   * initializations on the model before it is returned to the {@code TrackedNodeModel} object. This is needed by some
   * dynamic configuration implementations, for example by {@code CombinedConfiguration}.
   * </p>
   * <p>
   * If the tracked node acting as root node is exclusively used by this model, it should be released when this model is
   * no longer needed. This can be done manually by calling the {@link #close()} method. It is also possible to pass a
   * value of <strong>true</strong> to the {@code untrackOnFinalize} argument of the constructor. This causes
   * {@code close()} to be called automatically if this object gets claimed by the garbage collector.
   * </p>
   * <p>
   * As {@code InMemoryNodeModel}, this class is thread-safe.
   * </p>
   *
   * @since 2.0
   */
  public class TrackedNodeModel implements NodeModel<ImmutableNode> {
  
      /** Stores the underlying parent model. */
      private final InMemoryNodeModelSupport parentModelSupport;
  
      /** The selector for the managed tracked node. */
      private final NodeSelector selector;
  
      /**
       * A flag whether the tracked not should be released when this object is finalized.
       */
      private final boolean releaseTrackedNodeOnFinalize;
  
      /** A flag whether this model has already been closed. */
      private final AtomicBoolean closed;
  
      /**
       * Creates a new instance of {@code TrackedNodeModel} and initializes it with the given underlying model and the
       * selector to the root node. The boolean argument controls whether the associated tracked node should be released when
       * this object gets finalized. This allows the underlying model to free some resources. If used as model within a
       * {@code SubnodeConfiguration}, there is typically no way to discard the model explicitly. Therefore, it makes sense to
       * do this automatically on finalization.
       *
       * @param modelSupport the underlying {@code InMemoryNodeModelSupport} (must not be <strong>null</strong>)
       * @param sel the selector to the root node of this model (must not be <strong>null</strong>)
       * @param untrackOnFinalize a flag whether the tracked node should be released on finalization
       * @throws IllegalArgumentException if a required parameter is missing
       */
      public TrackedNodeModel(final InMemoryNodeModelSupport modelSupport, final NodeSelector sel, final boolean untrackOnFinalize) {
          if (modelSupport == null) {
              throw new IllegalArgumentException("Underlying model support must not be null!");
          }
          if (sel == null) {
              throw new IllegalArgumentException("Selector must not be null!");
          }
  
          parentModelSupport = modelSupport;
          selector = sel;
          releaseTrackedNodeOnFinalize = untrackOnFinalize;
          closed = new AtomicBoolean();
      }
  
      @Override
      public void addNodes(final String key, final Collection<? extends ImmutableNode> nodes, final NodeKeyResolver<ImmutableNode> resolver) {
          getParentModel().addNodes(key, getSelector(), nodes, resolver);
     }
 
     @Override
     public void addProperty(final String key, final Iterable<?> values, final NodeKeyResolver<ImmutableNode> resolver) {
         getParentModel().addProperty(key, getSelector(), values, resolver);
     }
 
     /**
      * {@inheritDoc} This implementation clears the sub tree spanned by the associate tracked node. This has the side effect
      * that this in any case becomes detached.
      *
      * @param resolver the {@code NodeKeyResolver}.
      */
     @Override
     public void clear(final NodeKeyResolver<ImmutableNode> resolver) {
         getParentModel().clearTree(null, getSelector(), resolver);
     }
 
     @Override
     public void clearProperty(final String key, final NodeKeyResolver<ImmutableNode> resolver) {
         getParentModel().clearProperty(key, getSelector(), resolver);
     }
 
     @Override
     public List<QueryResult<ImmutableNode>> clearTree(final String key, final NodeKeyResolver<ImmutableNode> resolver) {
         return getParentModel().clearTree(key, getSelector(), resolver);
     }
 
     /**
      * Closes this model. This causes the tracked node this model is based upon to be released (i.e.
      * {@link InMemoryNodeModel#untrackNode(NodeSelector)} is called). This method should be called when this model is no
      * longer needed. This implementation is idempotent; it is safe to call {@code close()} multiple times - only the first
      * invocation has an effect. After this method has been called this model can no longer be used because there is no
      * guarantee that the node can still be accessed from the parent model.
      */
     public void close() {
         if (closed.compareAndSet(false, true)) {
             getParentModel().untrackNode(getSelector());
         }
     }
 
     /**
      * {@inheritDoc} This implementation calls {@code close()} if the {@code untrackOnFinalize} flag was set when this
      * instance was constructed. While this is not 100 percent reliable, it is better than keeping the tracked node hanging
      * around. Note that it is not a problem if {@code close()} already had been invoked manually because this method is
      * idempotent.
      *
      * @see #close()
      */
     @Override
     protected void finalize() throws Throwable {
         if (isReleaseTrackedNodeOnFinalize()) {
             close();
         }
         super.finalize();
     }
 
     /**
      * {@inheritDoc} This implementation returns the tracked node instance acting as root node of this model.
      */
     @Override
     public ImmutableNode getInMemoryRepresentation() {
         return getNodeHandler().getRootNode();
     }
 
     @Override
     public NodeHandler<ImmutableNode> getNodeHandler() {
         return getParentModel().getTrackedNodeHandler(getSelector());
     }
 
     /**
      * Gets the parent model. Operations on this model are delegated to this parent model specifying the selector to the
      * tracked node.
      *
      * @return the parent model
      */
     public InMemoryNodeModel getParentModel() {
         return getParentModelSupport().getNodeModel();
     }
 
     /**
      * Gets the {@code InMemoryNodeModelSupport} object which is used to gain access to the underlying node model.
      *
      * @return the associated {@code InMemoryNodeModelSupport} object
      */
     public InMemoryNodeModelSupport getParentModelSupport() {
         return parentModelSupport;
     }
 
     /**
      * Gets the {@code NodeSelector} pointing to the tracked node managed by this model.
      *
      * @return the tracked node selector
      */
     public NodeSelector getSelector() {
         return selector;
     }
 
     /**
      * Returns the flag whether the managed tracked node is to be released when this object gets finalized. This method
      * returns the value of the corresponding flag passed to the constructor. If result is true, the underlying model is
      * asked to untrack the managed node when this object is claimed by the GC.
      *
      * @return a flag whether the managed tracked node should be released when this object dies
      * @see InMemoryNodeModel#untrackNode(NodeSelector)
      */
     public boolean isReleaseTrackedNodeOnFinalize() {
         return releaseTrackedNodeOnFinalize;
     }
 
     @Override
     public void setProperty(final String key, final Object value, final NodeKeyResolver<ImmutableNode> resolver) {
         getParentModel().setProperty(key, getSelector(), value, resolver);
     }
 
     @Override
     public void setRootNode(final ImmutableNode newRoot) {
         getParentModel().replaceTrackedNode(getSelector(), newRoot);
     }
 }