Added highlight offset for highlighted terms in fragments

modules/elasticsearch/src/main/java/org/apache/lucene/search/vectorhighlight/MarginFragListBuilder.java

@@ -0,0 +1,96 @@
+/*
+ * Licensed to Elastic Search and Shay Banon under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. Elastic Search 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 simple implementation of {@link FragListBuilder}.
+ */
+public class MarginFragListBuilder implements FragListBuilder {
+
+  private static final int DEFAULT_MARGIN = 6;
+  private int margin;
+  private int minFragCharSize;
+
+  public MarginFragListBuilder() {
+   this(DEFAULT_MARGIN);
+  }
+
+  public MarginFragListBuilder(int startMargin) {
+    margin = startMargin;
+    minFragCharSize = 3*margin;
+  }
+
+  public FieldFragList createFieldFragList(FieldPhraseList fieldPhraseList, int fragCharSize) {
+    if( fragCharSize < minFragCharSize )
+      throw new IllegalArgumentException( "fragCharSize(" + fragCharSize + ") is too small. It must be " +
+          minFragCharSize + " or higher." );
+
+    FieldFragList ffl = new FieldFragList( fragCharSize );
+
+    List<WeightedPhraseInfo> wpil = new ArrayList<WeightedPhraseInfo>();
+    Iterator<WeightedPhraseInfo> ite = fieldPhraseList.phraseList.iterator();
+    WeightedPhraseInfo phraseInfo = null;
+    int startOffset = 0;
+    boolean taken = false;
+    while( true ){
+      if( !taken ){
+        if( !ite.hasNext() ) break;
+        phraseInfo = ite.next();
+      }
+      taken = false;
+      if( phraseInfo == null ) break;
+
+      // if the phrase violates the border of previous fragment, discard it and try next phrase
+      if( phraseInfo.getStartOffset() < startOffset ) continue;
+
+      wpil.clear();
+      wpil.add( phraseInfo );
+      int st = phraseInfo.getStartOffset() - margin < startOffset ?
+          startOffset : phraseInfo.getStartOffset() - margin;
+      int en = st + fragCharSize;
+      if( phraseInfo.getEndOffset() > en )
+        en = phraseInfo.getEndOffset();
+      startOffset = en;
+
+      while( true ){
+        if( ite.hasNext() ){
+          phraseInfo = ite.next();
+          taken = true;
+          if( phraseInfo == null ) break;
+        }
+        else
+          break;
+        if( phraseInfo.getEndOffset() <= en )
+          wpil.add( phraseInfo );
+        else
+          break;
+      }
+      ffl.add( st, en, wpil );
+    }
+    return ffl;
+  }
+
+}

modules/elasticsearch/src/main/java/org/elasticsearch/search/highlight/HighlightPhase.java

@@ -223,13 +223,18 @@ private FastVectorHighlighter buildHighlighter(SearchContext searchContext, Fiel
         FragmentsBuilder fragmentsBuilder;
         if (field.numberOfFragments() == 0) {
             fragListBuilder = new SingleFragListBuilder();
+
             if (fieldMapper.stored()) {
                 fragmentsBuilder = new SimpleFragmentsBuilder(field.preTags(), field.postTags());
             } else {
                 fragmentsBuilder = new SourceSimpleFragmentsBuilder(fieldMapper, searchContext, field.preTags(), field.postTags());
             }
         } else {
-            fragListBuilder = new SimpleFragListBuilder();
+            if(field.fragmentOffset() == -1)
+                fragListBuilder = new SimpleFragListBuilder();
+            else
+                fragListBuilder = new MarginFragListBuilder(field.fragmentOffset());
+
             if (field.scoreOrdered()) {
                 if (fieldMapper.stored()) {
                     fragmentsBuilder = new ScoreOrderFragmentsBuilder(field.preTags(), field.postTags());

modules/elasticsearch/src/main/java/org/elasticsearch/search/highlight/HighlighterParseElement.java

@@ -137,6 +137,8 @@ public class HighlighterParseElement implements SearchParseElement {
                                         field.fragmentCharSize(parser.intValue());
                                     } else if ("number_of_fragments".equals(fieldName) || "numberOfFragments".equals(fieldName)) {
                                         field.numberOfFragments(parser.intValue());
+                                    } else if ("fragment_offset".equals(fieldName) || "fragmentOffset".equals(fieldName)) {
+                                        field.fragmentOffset(parser.intValue());
                                     } else if ("highlight_filter".equals(fieldName) || "highlightFilter".equals(fieldName)) {
                                         field.highlightFilter(parser.booleanValue());
                                     } else if ("score".equals(fieldName)) {

modules/elasticsearch/src/main/java/org/elasticsearch/search/highlight/SearchContextHighlight.java

@@ -44,6 +44,8 @@ public static class Field {
 
         private int numberOfFragments = -1;
 
+        private int fragmentOffset = -1;
+
         private String[] preTags;
 
         private String[] postTags;
@@ -76,6 +78,14 @@ public void numberOfFragments(int numberOfFragments) {
             this.numberOfFragments = numberOfFragments;
         }
 
+        public int fragmentOffset() {
+            return fragmentOffset;
+        }
+
+        public void fragmentOffset(int fragmentOffset) {
+            this.fragmentOffset = fragmentOffset;
+        }
+
         public String[] preTags() {
             return preTags;
         }