/*
 * 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.search.vectorhighlight;

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

import org.apache.lucene.search.vectorhighlight.FieldPhraseList.WeightedPhraseInfo;

A abstract implementation of FragListBuilder. /**
 * A abstract implementation of {@link FragListBuilder}.
 */
public abstract class BaseFragListBuilder implements FragListBuilder {
  
  public static final int MARGIN_DEFAULT = 6;
  public static final int MIN_FRAG_CHAR_SIZE_FACTOR = 3;

  final int margin;
  final int minFragCharSize;

  public BaseFragListBuilder( int margin ){
    if( margin < 0 )
      throw new IllegalArgumentException( "margin(" + margin + ") is too small. It must be 0 or higher." );

    this.margin = margin;
    this.minFragCharSize = Math.max( 1, margin * MIN_FRAG_CHAR_SIZE_FACTOR );
  }

  public BaseFragListBuilder(){
    this( MARGIN_DEFAULT );
  }
  
 protected FieldFragList createFieldFragList( FieldPhraseList fieldPhraseList, FieldFragList fieldFragList, int fragCharSize ){
    if( fragCharSize < minFragCharSize )
      throw new IllegalArgumentException( "fragCharSize(" + fragCharSize + ") is too small. It must be " + minFragCharSize + " or higher." );
    
    List<WeightedPhraseInfo> wpil = new ArrayList<>();
    IteratorQueue<WeightedPhraseInfo> queue = new IteratorQueue<>(fieldPhraseList.getPhraseList().iterator());
    WeightedPhraseInfo phraseInfo = null;
    int startOffset = 0;
    while((phraseInfo = queue.top()) != null){
      // if the phrase violates the border of previous fragment, discard it and try next phrase
      if( phraseInfo.getStartOffset() < startOffset )  {
        queue.removeTop();
        continue;
      }
      
      wpil.clear();
      final int currentPhraseStartOffset = phraseInfo.getStartOffset();
      int currentPhraseEndOffset = phraseInfo.getEndOffset();
      int spanStart = Math.max(currentPhraseStartOffset - margin, startOffset);
      int spanEnd = Math.max(currentPhraseEndOffset, spanStart + fragCharSize);
      if (acceptPhrase(queue.removeTop(),  currentPhraseEndOffset - currentPhraseStartOffset, fragCharSize)) {
        wpil.add(phraseInfo);
      }
      while((phraseInfo = queue.top()) != null) { // pull until we crossed the current spanEnd
        if (phraseInfo.getEndOffset() <= spanEnd) {
          currentPhraseEndOffset = phraseInfo.getEndOffset();
          if (acceptPhrase(queue.removeTop(),  currentPhraseEndOffset - currentPhraseStartOffset, fragCharSize)) {
            wpil.add(phraseInfo);
          }
        } else {
          break;
        }
      }
      if (wpil.isEmpty()) {
        continue;
      }
      
      final int matchLen = currentPhraseEndOffset - currentPhraseStartOffset;
      // now recalculate the start and end position to "center" the result
      final int newMargin = Math.max(0, (fragCharSize-matchLen)/2); // matchLen can be > fragCharSize prevent IAOOB here
      spanStart = currentPhraseStartOffset - newMargin;
      if (spanStart < startOffset) {
        spanStart = startOffset;
      }
      // whatever is bigger here we grow this out
      spanEnd = spanStart + Math.max(matchLen, fragCharSize);  
      startOffset = spanEnd;
      fieldFragList.add(spanStart, spanEnd, wpil);
    }
    return fieldFragList;
  }
 
  
A predicate to decide if the given WeightedPhraseInfo should be accepted as a highlighted phrase or if it should be discarded. 

The default implementation discards phrases that are composed of more than one term
and where the matchLength exceeds the fragment character size.
Params:
info – the phrase info to accept
matchLength – the match length of the current phrase
fragCharSize – the configured fragment character size
Returns:
true if this phrase info should be accepted as a highligh phrase/**
   * A predicate to decide if the given {@link WeightedPhraseInfo} should be
   * accepted as a highlighted phrase or if it should be discarded.
   * <p>
   * The default implementation discards phrases that are composed of more than one term
   * and where the matchLength exceeds the fragment character size.
   * 
   * @param info the phrase info to accept
   * @param matchLength the match length of the current phrase
   * @param fragCharSize the configured fragment character size
   * @return <code>true</code> if this phrase info should be accepted as a highligh phrase
   */
 protected boolean acceptPhrase(WeightedPhraseInfo info, int matchLength, int fragCharSize) {
   return info.getTermsOffsets().size() <= 1 ||  matchLength <= fragCharSize;
 }
 
 private static final class IteratorQueue<T> {
   private final Iterator<T> iter;
   private T top;
   
   public IteratorQueue(Iterator<T> iter) {
     this.iter = iter;
     T removeTop = removeTop();
     assert removeTop == null;
   }
   
   public T top() {
     return top;
   }
   
   public T removeTop() {
     T currentTop = top;
     if (iter.hasNext()) {
       top = iter.next();
     } else {
       top = null;
     }
     return currentTop;
   }
   
 }
 
}