Refactor append logic

Signed-off-by: Tomoyuki Morita <[email protected]>

Author: ykmr1224

core/src/main/java/org/opensearch/sql/calcite/ExtendedRexBuilder.java

@@ -6,6 +6,7 @@
 package org.opensearch.sql.calcite;
 
 import com.google.common.collect.ImmutableList;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Locale;
@@ -179,7 +180,7 @@ public RexNode createStringArrayLiteral(List<String> values) {
     RelDataType stringType = getTypeFactory().createSqlType(SqlTypeName.VARCHAR);
     RelDataType arrayType = getTypeFactory().createArrayType(stringType, -1);
 
-    List<RexNode> elements = new java.util.ArrayList<>();
+    List<RexNode> elements = new ArrayList<>();
     for (String value : values) {
       elements.add(makeLiteral(value));
     }

core/src/main/java/org/opensearch/sql/expression/function/CollectionUDF/AppendCore.java

@@ -8,14 +8,32 @@
 import java.util.ArrayList;
 import java.util.List;
 
-/** Core logic for internal `append` function to collect elements from list of args. */
+/**
+ * Core logic for `mvappend` and internal `append` function to collect elements from list of args.
+ */
 public class AppendCore {
 
   /**
    * Collect non-null elements from `args`. If an item is a list, it will collect non-null elements
    * of the list. See {@ref AppendFunctionImplTest} for detailed behavior.
    */
   public static Object collectElements(Object... args) {
+    List<Object> elements = collectElementsToList(args);
+
+    if (elements.isEmpty()) {
+      return null;
+    } else if (elements.size() == 1) {
+      // return the element in case of single element
+      return elements.get(0);
+    } else {
+      return elements;
+    }
+  }
+
+  /**
+   * Collect non-null elements from `args`. If an item is a list, it will collect non-null elements.
+   */
+  public static List<Object> collectElementsToList(Object... args) {
     List<Object> elements = new ArrayList<>();
 
     for (Object arg : args) {
@@ -28,14 +46,7 @@ public static Object collectElements(Object... args) {
       }
     }
 
-    if (elements.isEmpty()) {
-      return null;
-    } else if (elements.size() == 1) {
-      // return the element in case of single element
-      return elements.get(0);
-    } else {
-      return elements;
-    }
+    return elements;
   }
 
   private static void addListElements(List<?> list, List<Object> elements) {

core/src/main/java/org/opensearch/sql/expression/function/CollectionUDF/MVAppendFunctionImpl.java

@@ -7,7 +7,6 @@
 
 import static org.apache.calcite.sql.type.SqlTypeUtil.createArrayType;
 
-import java.util.ArrayList;
 import java.util.List;
 import org.apache.calcite.adapter.enumerable.NotNullImplementor;
 import org.apache.calcite.adapter.enumerable.NullPolicy;
@@ -106,26 +105,7 @@ public static Object mvappend(Object... args) {
    * of the list. See {@ref MVAppendFunctionImplTest} for detailed behavior.
    */
   public static List<Object> collectElements(Object... args) {
-    List<Object> elements = new ArrayList<>();
-
-    for (Object arg : args) {
-      if (arg == null) {
-        continue;
-      } else if (arg instanceof List) {
-        addListElements((List<?>) arg, elements);
-      } else {
-        elements.add(arg);
-      }
-    }
-
-    return elements.size() == 0 ? null : elements;
-  }
-
-  private static void addListElements(List<?> list, List<Object> elements) {
-    for (Object item : list) {
-      if (item != null) {
-        elements.add(item);
-      }
-    }
+    List<Object> elements = AppendCore.collectElementsToList(args);
+    return elements.isEmpty() ? null : elements;
   }
 }