/*
 * 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.lucene.index;


import java.io.IOException;
import java.util.List;

A FilterDirectoryReader wraps another DirectoryReader, allowing implementations
to transform or extend it.
Subclasses should implement doWrapDirectoryReader to return an instance of the
subclass.
If the subclass wants to wrap the DirectoryReader's subreaders, it should also
implement a SubReaderWrapper subclass, and pass an instance to its super
constructor.
/**
 * A FilterDirectoryReader wraps another DirectoryReader, allowing implementations
 * to transform or extend it.
 *
 * Subclasses should implement doWrapDirectoryReader to return an instance of the
 * subclass.
 *
 * If the subclass wants to wrap the DirectoryReader's subreaders, it should also
 * implement a SubReaderWrapper subclass, and pass an instance to its super
 * constructor.
 */
public abstract class FilterDirectoryReader extends DirectoryReader {

  
Get the wrapped instance by reader as long as this reader is an instance of FilterDirectoryReader. /** Get the wrapped instance by <code>reader</code> as long as this reader is
   *  an instance of {@link FilterDirectoryReader}.  */
  public static DirectoryReader unwrap(DirectoryReader reader) {
    while (reader instanceof FilterDirectoryReader) {
      reader = ((FilterDirectoryReader) reader).getDelegate();
    }
    return reader;
  }

  
Factory class passed to FilterDirectoryReader constructor that allows
subclasses to wrap the filtered DirectoryReader's subreaders.  You
can use this to, e.g., wrap the subreaders with specialised
FilterLeafReader implementations.
/**
   * Factory class passed to FilterDirectoryReader constructor that allows
   * subclasses to wrap the filtered DirectoryReader's subreaders.  You
   * can use this to, e.g., wrap the subreaders with specialised
   * FilterLeafReader implementations.
   */
  public static abstract class SubReaderWrapper {

    
Wraps a list of LeafReaders
Returns:
an array of wrapped LeafReaders. The returned array might contain less elements compared to the given
reader list if an entire reader is filtered out./**
     * Wraps a list of LeafReaders
     * @return an array of wrapped LeafReaders. The returned array might contain less elements compared to the given
     * reader list if an entire reader is filtered out.
     */
    protected LeafReader[] wrap(List<? extends LeafReader> readers) {
      LeafReader[] wrapped = new LeafReader[readers.size()];
      int i = 0;
      for (LeafReader reader : readers) {
        LeafReader wrap = wrap(reader);
        assert wrap != null;
        wrapped[i++] = wrap;
      }
      return wrapped;
    }

    
Constructor /** Constructor */
    public SubReaderWrapper() {}

    
Wrap one of the parent DirectoryReader's subreaders
Params:
reader – the subreader to wrap
Returns:
a wrapped/filtered LeafReader/**
     * Wrap one of the parent DirectoryReader's subreaders
     * @param reader the subreader to wrap
     * @return a wrapped/filtered LeafReader
     */
    public abstract LeafReader wrap(LeafReader reader);

  }

  
The filtered DirectoryReader /** The filtered DirectoryReader */
  protected final DirectoryReader in;

  
Create a new FilterDirectoryReader that filters a passed in DirectoryReader,
using the supplied SubReaderWrapper to wrap its subreader.
Params:
in – the DirectoryReader to filter
wrapper – the SubReaderWrapper to use to wrap subreaders/**
   * Create a new FilterDirectoryReader that filters a passed in DirectoryReader,
   * using the supplied SubReaderWrapper to wrap its subreader.
   * @param in the DirectoryReader to filter
   * @param wrapper the SubReaderWrapper to use to wrap subreaders
   */
  public FilterDirectoryReader(DirectoryReader in, SubReaderWrapper wrapper) throws IOException {
    super(in.directory(), wrapper.wrap(in.getSequentialSubReaders()));
    this.in = in;
  }

  
Called by the doOpenIfChanged() methods to return a new wrapped DirectoryReader.
Implementations should just return an instantiation of themselves, wrapping the
passed in DirectoryReader.
Params:
in – the DirectoryReader to wrap
Returns:
the wrapped DirectoryReader/**
   * Called by the doOpenIfChanged() methods to return a new wrapped DirectoryReader.
   *
   * Implementations should just return an instantiation of themselves, wrapping the
   * passed in DirectoryReader.
   *
   * @param in the DirectoryReader to wrap
   * @return the wrapped DirectoryReader
   */
  protected abstract DirectoryReader doWrapDirectoryReader(DirectoryReader in) throws IOException;

  private final DirectoryReader wrapDirectoryReader(DirectoryReader in) throws IOException {
    return in == null ? null : doWrapDirectoryReader(in);
  }

  @Override
  protected final DirectoryReader doOpenIfChanged() throws IOException {
    return wrapDirectoryReader(in.doOpenIfChanged());
  }

  @Override
  protected final DirectoryReader doOpenIfChanged(IndexCommit commit) throws IOException {
    return wrapDirectoryReader(in.doOpenIfChanged(commit));
  }

  @Override
  protected final DirectoryReader doOpenIfChanged(IndexWriter writer, boolean applyAllDeletes) throws IOException {
    return wrapDirectoryReader(in.doOpenIfChanged(writer, applyAllDeletes));
  }

  @Override
  public long getVersion() {
    return in.getVersion();
  }

  @Override
  public boolean isCurrent() throws IOException {
    return in.isCurrent();
  }

  @Override
  public IndexCommit getIndexCommit() throws IOException {
    return in.getIndexCommit();
  }

  @Override
  protected void doClose() throws IOException {
    in.close();
  }

  
Returns the wrapped DirectoryReader. /** Returns the wrapped {@link DirectoryReader}. */
  public DirectoryReader getDelegate() {
    return in;
  }
}