/*
 * 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.analysis.sinks;


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

import org.apache.lucene.analysis.TokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.util.AttributeSource;

This TokenFilter provides the ability to set aside attribute states that have already been analyzed. This is useful
in situations where multiple fields share many common analysis steps and then go their separate ways.

It is also useful for doing things like entity extraction or proper noun analysis as part of the analysis workflow
and saving off those tokens for use in another field.

TeeSinkTokenFilter source1 = new TeeSinkTokenFilter(new WhitespaceTokenizer());
TeeSinkTokenFilter.SinkTokenStream sink1 = source1.newSinkTokenStream();
TeeSinkTokenFilter.SinkTokenStream sink2 = source1.newSinkTokenStream();
TokenStream final1 = new LowerCaseFilter(source1);
TokenStream final2 = new EntityDetect(sink1);
TokenStream final3 = new URLDetect(sink2);
d.add(new TextField("f1", final1));
d.add(new TextField("f2", final2));
d.add(new TextField("f3", final3));

 In this example, sink1 and sink2 will both get tokens from source1 after whitespace tokenization, and will further do additional token filtering, e.g. detect entities and URLs. 

NOTE: it is important, that tees are consumed before sinks, therefore you should add them to the document
before the sinks. In the above example, f1 is added before the other fields, and so by the time they are processed, it has already been consumed, which is the correct way to index the three streams. If for some reason you cannot ensure that, you should call consumeAllTokens() before adding the sinks to document fields. /**
 * This TokenFilter provides the ability to set aside attribute states that have already been analyzed. This is useful
 * in situations where multiple fields share many common analysis steps and then go their separate ways.
 * 
 * <p>
 * It is also useful for doing things like entity extraction or proper noun analysis as part of the analysis workflow
 * and saving off those tokens for use in another field.
 * </p>
 *
 * <pre class="prettyprint">
 * TeeSinkTokenFilter source1 = new TeeSinkTokenFilter(new WhitespaceTokenizer());
 * TeeSinkTokenFilter.SinkTokenStream sink1 = source1.newSinkTokenStream();
 * TeeSinkTokenFilter.SinkTokenStream sink2 = source1.newSinkTokenStream();
 *
 * TokenStream final1 = new LowerCaseFilter(source1);
 * TokenStream final2 = new EntityDetect(sink1);
 * TokenStream final3 = new URLDetect(sink2);
 *
 * d.add(new TextField("f1", final1));
 * d.add(new TextField("f2", final2));
 * d.add(new TextField("f3", final3));
 * </pre>
 * 
 * <p>
 * In this example, {@code sink1} and {@code sink2} will both get tokens from {@code source1} after whitespace
 * tokenization, and will further do additional token filtering, e.g. detect entities and URLs.
 * </p>
 * 
 * <p>
 * <b>NOTE</b>: it is important, that tees are consumed before sinks, therefore you should add them to the document
 * before the sinks. In the above example, <i>f1</i> is added before the other fields, and so by the time they are
 * processed, it has already been consumed, which is the correct way to index the three streams. If for some reason you
 * cannot ensure that, you should call {@link #consumeAllTokens()} before adding the sinks to document fields.
 */
public final class TeeSinkTokenFilter extends TokenFilter {

  private final States cachedStates = new States();

  public TeeSinkTokenFilter(TokenStream input) {
    super(input);
  }

  
Returns a new SinkTokenStream that receives all tokens consumed by this stream. /** Returns a new {@link SinkTokenStream} that receives all tokens consumed by this stream. */
  public TokenStream newSinkTokenStream() {
    return new SinkTokenStream(this.cloneAttributes(), cachedStates);
  }

  
TeeSinkTokenFilter passes all tokens to the added sinks when itself is consumed. To be sure that all
tokens from the input stream are passed to the sinks, you can call this methods. This instance is exhausted after
this method returns, but all sinks are instant available.
/**
   * <code>TeeSinkTokenFilter</code> passes all tokens to the added sinks when itself is consumed. To be sure that all
   * tokens from the input stream are passed to the sinks, you can call this methods. This instance is exhausted after
   * this method returns, but all sinks are instant available.
   */
  public void consumeAllTokens() throws IOException {
    while (incrementToken()) {}
  }

  @Override
  public boolean incrementToken() throws IOException {
    if (input.incrementToken()) {
      cachedStates.add(captureState());
      return true;
    }

    return false;
  }

  @Override
  public final void end() throws IOException {
    super.end();
    cachedStates.setFinalState(captureState());
  }

  @Override
  public void reset() throws IOException {
    cachedStates.reset();
    super.reset();
  }

  
TokenStream output from a tee. /** TokenStream output from a tee. */
  public static final class SinkTokenStream extends TokenStream {
    private final States cachedStates;
    private Iterator<AttributeSource.State> it = null;

    private SinkTokenStream(AttributeSource source, States cachedStates) {
      super(source);
      this.cachedStates = cachedStates;
    }

    @Override
    public final boolean incrementToken() {
      if (!it.hasNext()) {
        return false;
      }

      AttributeSource.State state = it.next();
      restoreState(state);
      return true;
    }

    @Override
    public void end() throws IOException {
      State finalState = cachedStates.getFinalState();
      if (finalState != null) {
        restoreState(finalState);
      }
    }

    @Override
    public final void reset() {
      it = cachedStates.getStates();
    }
  }

  
A convenience wrapper for storing the cached states as well the final state of the stream. /** A convenience wrapper for storing the cached states as well the final state of the stream. */
  private static final class States {

    private final List<State> states = new ArrayList<>();
    private State finalState;

    public States() {}

    void setFinalState(State finalState) {
      this.finalState = finalState;
    }

    State getFinalState() {
      return finalState;
    }

    void add(State state) {
      states.add(state);
    }

    Iterator<State> getStates() {
      return states.iterator();
    }

    void reset() {
      finalState = null;
      states.clear();
    }
  }

}