Refactor to better show the intention of reducability.

4 files changed, 37 insertions, 13 deletions

diff --git a/container-search/src/main/java/com/yahoo/prelude/query/CompositeItem.java b/container-search/src/main/java/com/yahoo/prelude/query/CompositeItem.java
index 907eabe60ce..4bc15d3c897 100644
--- a/container-search/src/main/java/com/yahoo/prelude/query/CompositeItem.java
+++ b/container-search/src/main/java/com/yahoo/prelude/query/CompositeItem.java
@@ -13,6 +13,7 @@ import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
 import java.util.ListIterator;
+import java.util.Optional;
 
 
 /**
@@ -379,4 +380,12 @@ public abstract class CompositeItem extends Item {
         return terms;
     }
 
+    /**
+     * Will return its single child if itself can safely be ommitted.
+     * @return A valid Item or empty Optional if it can not be done.
+     */
+    public Optional<Item> extractSingleChild() {
+        return getItemCount() == 1 ? Optional.of(getItem(0)) : Optional.empty();
+    }
+
 }
diff --git a/container-search/src/main/java/com/yahoo/prelude/query/NonReducibleCompositeItem.java b/container-search/src/main/java/com/yahoo/prelude/query/NonReducibleCompositeItem.java
index 84aa177369a..97d724953ea 100644
--- a/container-search/src/main/java/com/yahoo/prelude/query/NonReducibleCompositeItem.java
+++ b/container-search/src/main/java/com/yahoo/prelude/query/NonReducibleCompositeItem.java
@@ -1,6 +1,8 @@
 // Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package com.yahoo.prelude.query;
 
+import java.util.Optional;
+
 /**
  * A composite item which specifies semantics which are not maintained
  * if an instance with a single child is replaced by the single child.
@@ -12,4 +14,8 @@ package com.yahoo.prelude.query;
  * @author bratseth
  */
 public abstract class NonReducibleCompositeItem extends CompositeItem {
+    @Override
+    public Optional<Item> extractSingleChild() {
+        return Optional.empty();
+    }
 }
diff --git a/container-search/src/main/java/com/yahoo/prelude/query/QueryCanonicalizer.java b/container-search/src/main/java/com/yahoo/prelude/query/QueryCanonicalizer.java
index 2fbda1a9c32..23030abe102 100644
--- a/container-search/src/main/java/com/yahoo/prelude/query/QueryCanonicalizer.java
+++ b/container-search/src/main/java/com/yahoo/prelude/query/QueryCanonicalizer.java
@@ -4,7 +4,10 @@ package com.yahoo.prelude.query;
 import com.yahoo.search.Query;
 import com.yahoo.search.query.QueryTree;
 
-import java.util.*;
+import java.util.HashSet;
+import java.util.ListIterator;
+import java.util.Optional;
+import java.util.Set;
 
 /**
  * Query normalizer and sanity checker.
@@ -82,21 +85,16 @@ public class QueryCanonicalizer {
         if (composite.getItemCount() == 0)
             parentIterator.remove();
 
-        if (composite.getItemCount() == 1 && ! (composite instanceof NonReducibleCompositeItem)) {
-            Item child = composite.getItem(0);
-            if (composite instanceof PhraseItem || composite instanceof PhraseSegmentItem)
-                child.setWeight(composite.getWeight());
-            parentIterator.set(child);
-        }
-        if ((composite.getItemCount() == 1) && (composite instanceof SameElementItem)) {
-            SameElementItem sameElement = (SameElementItem) composite;
-            WordItem child = (WordItem) sameElement.getItem(0);
-            child.setIndexName(sameElement.getFieldName() + "." + child.getIndexName());
-            parentIterator.set(child);
-        }
+        composite.extractSingleChild().ifPresent( (Item child) -> reduce(composite, parentIterator, child));
 
         return CanonicalizationResult.success();
     }
+
+    private static void reduce(CompositeItem composite, ListIterator<Item> parentIterator, Item child) {
+        if (composite instanceof PhraseItem || composite instanceof PhraseSegmentItem)
+            child.setWeight(composite.getWeight());
+        parentIterator.set(child);
+    }
     
     private static void collapseLevels(CompositeItem composite) {
         if (composite instanceof RankItem || composite instanceof NotItem) {
diff --git a/container-search/src/main/java/com/yahoo/prelude/query/SameElementItem.java b/container-search/src/main/java/com/yahoo/prelude/query/SameElementItem.java
index aa446140da0..d2c19339298 100644
--- a/container-search/src/main/java/com/yahoo/prelude/query/SameElementItem.java
+++ b/container-search/src/main/java/com/yahoo/prelude/query/SameElementItem.java
@@ -6,6 +6,7 @@ import com.yahoo.protect.Validator;
 
 import java.nio.ByteBuffer;
 import java.util.Iterator;
+import java.util.Optional;
 
 /**
  * This represents a query where all terms are required to match in the same element id.
@@ -54,6 +55,16 @@ public class SameElementItem extends NonReducibleCompositeItem {
         Validator.ensureNonEmpty("Struct fieldname", asTerm.getIndexName());
         Validator.ensureNonEmpty("Query term", asTerm.getIndexedString());
     }
+
+    @Override
+    public Optional<Item> extractSingleChild() {
+        if (getItemCount() == 1) {
+            WordItem child = (WordItem) getItem(0);
+            child.setIndexName(getFieldName() + "." + child.getIndexName());
+            return Optional.of(child);
+        }
+        return Optional.empty();
+    }
     
     @Override
     public ItemType getItemType() {