dungba88 commented on code in PR #14776:
URL: https://github.com/apache/lucene/pull/14776#discussion_r2144454143


##########
lucene/core/src/java/org/apache/lucene/search/DoubleValuesSourceRescorer.java:
##########
@@ -0,0 +1,133 @@
+/*
+ * 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;
+
+import java.io.IOException;
+import java.util.Arrays;
+import java.util.List;
+import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.util.ArrayUtil;
+
+/** A {@link Rescorer} that uses provided DoubleValuesSource to rescore first 
pass hits. */
+public abstract class DoubleValuesSourceRescorer extends Rescorer {
+
+  private final DoubleValuesSource valuesSource;
+
+  public DoubleValuesSourceRescorer(DoubleValuesSource valuesSource) {
+    this.valuesSource = valuesSource;
+  }
+
+  /**
+   * Implement this in a subclass to combine the first pass scores with values 
from the
+   * DoubleValuesSource
+   *
+   * @param firstPassScore Score from firstPassTopDocs
+   * @param valuePresent true if DoubleValuesSource has a value for the hit 
from first pass
+   * @param sourceValue Value returned from DoubleValuesSource
+   */
+  protected abstract float combine(float firstPassScore, boolean valuePresent, 
double sourceValue);
+
+  @Override
+  public TopDocs rescore(IndexSearcher searcher, TopDocs firstPassTopDocs, int 
topN)
+      throws IOException {
+    DoubleValuesSource source = valuesSource.rewrite(searcher);
+    // this will still alter scores, we clone to retain hits ordering in 
firstPassTopDocs
+    ScoreDoc[] hits = firstPassTopDocs.scoreDocs.clone();
+    Arrays.sort(hits, (a, b) -> a.doc - b.doc);
+
+    List<LeafReaderContext> leaves = searcher.getIndexReader().leaves();
+    LeafReaderContext ctx = leaves.getFirst();
+    int currLeaf = 0;
+    int leafEnd = ctx.docBase + ctx.reader().maxDoc();
+
+    // find leaf holding this doc
+    for (ScoreDoc hit : hits) {
+      while (hit.doc >= leafEnd) {
+        if (currLeaf == leaves.size() - 1) {
+          throw new IllegalStateException(
+              "hit docId="
+                  + hit.doc
+                  + "greater than last searcher leaf maxDoc="
+                  + leafEnd
+                  + " Ensure firstPassTopDocs were produced by the searcher 
provided to rescore.");
+        }
+        ctx = leaves.get(++currLeaf);
+        leafEnd = ctx.docBase + ctx.reader().maxDoc();
+      }
+
+      int targetDoc = hit.doc - ctx.docBase;
+      DoubleValues values = source.getValues(ctx, null);
+      boolean scorePresent = values.advanceExact(targetDoc);
+      double secondPassScore = scorePresent ? values.doubleValue() : 0.0f;
+      hit.score = combine(hit.score, scorePresent, secondPassScore);
+    }
+
+    if (topN < hits.length) {
+      ArrayUtil.select(hits, 0, hits.length, topN, 
ScoreDoc.scoreDocComparator);
+      ScoreDoc[] subset = new ScoreDoc[topN];
+      System.arraycopy(hits, 0, subset, 0, topN);
+      hits = subset;
+    }
+    Arrays.sort(hits, ScoreDoc.scoreDocComparator);
+
+    return new TopDocs(firstPassTopDocs.totalHits, hits);
+  }
+
+  @Override
+  public Explanation explain(IndexSearcher searcher, Explanation 
firstPassExplanation, int docID)
+      throws IOException {
+    Explanation first =
+        Explanation.match(
+            firstPassExplanation.getValue(), "first pass score", 
firstPassExplanation);
+
+    LeafReaderContext leafWithDoc = null;
+    for (LeafReaderContext ctx : searcher.getIndexReader().leaves()) {
+      if (docID >= ctx.docBase && docID < (ctx.docBase + 
ctx.reader().maxDoc())) {
+        leafWithDoc = ctx;
+        break;
+      }
+    }
+    if (leafWithDoc == null) {
+      throw new IllegalArgumentException(

Review Comment:
   Gotcha, thanks for the explanation. Maybe we can add some nuance you 
mentioned above to the error message, if the only possible case is a different 
IndexSearcher was passed? Anyhow, no strong opinion here.



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