Addres comments

Signed-off-by: Andy Kwok <[email protected]>

ppl-spark-integration/src/main/antlr4/OpenSearchPPLParser.g4

@@ -263,7 +263,8 @@ trendlineClause
    ;
 
 trendlineType
-   : (SMA | WMA)
+   : SMA
+   | WMA
    ;
 
 kmeansCommand

ppl-spark-integration/src/main/java/org/opensearch/sql/ppl/utils/TrendlineCatalystUtils.java

@@ -96,10 +96,19 @@ private static CaseWhen trendlineOrNullWhenThereAreTooFewDataPoints(CatalystExpr
      * Responsible to produce a Spark Logical Plan with given TrendLine command arguments, below is the sample logical plan
      * with configuration [dataField=salary, sortField=age, dataPoints=3]
      * -- +- 'Project [
-     * -- (((('nth_value('salary, 1) windowspecdefinition(Field(field=age, fieldArgs=[]) ASC NULLS FIRST, specifiedwindowframe(RowFrame, -1, currentrow$())) * 1) +
-     * -- ('nth_value('salary, 2) windowspecdefinition(Field(field=age, fieldArgs=[]) ASC NULLS FIRST, specifiedwindowframe(RowFrame, -1, currentrow$())) * 2)) +
-     * -- ('nth_value('salary, 3) windowspecdefinition(Field(field=age, fieldArgs=[]) ASC NULLS FIRST, specifiedwindowframe(RowFrame, -1, currentrow$())) * 3)) / 6)
+     * -- (((('nth_value('salary, 1) windowspecdefinition(Field(field=age, fieldArgs=[]) ASC NULLS FIRST, specifiedwindowframe(RowFrame, -2, currentrow$())) * 1) +
+     * -- ('nth_value('salary, 2) windowspecdefinition(Field(field=age, fieldArgs=[]) ASC NULLS FIRST, specifiedwindowframe(RowFrame, -2, currentrow$())) * 2)) +
+     * -- ('nth_value('salary, 3) windowspecdefinition(Field(field=age, fieldArgs=[]) ASC NULLS FIRST, specifiedwindowframe(RowFrame, -2, currentrow$())) * 3)) / 6)
      * -- AS WMA#702]
+     * .
+     * And the corresponded SQL query:
+     * .
+     * SELECT name, salary,
+     * (   nth_value(salary, 1) OVER (ORDER BY age ROWS BETWEEN 2 PRECEDING AND CURRENT ROW) *1 +
+     *     nth_value(salary, 2) OVER (ORDER BY age ROWS BETWEEN 2 PRECEDING AND CURRENT ROW) *2 +
+     *     nth_value(salary, 3) OVER (ORDER BY age ROWS BETWEEN 2 PRECEDING AND CURRENT ROW) *3  )/6 AS WMA
+     * FROM employees
+     * ORDER BY age;
      *
      * @param visitor Visitor instance to process any UnresolvedExpression.
      * @param node Trendline command's arguments.
@@ -113,7 +122,7 @@ private static NamedExpression getWMAComputationExpression(CatalystExpressionVis
                                                                CatalystPlanContext context) {
         int dataPoints = node.getNumberOfDataPoints();
         //window lower boundary
-        Expression windowLowerBoundary = getIntExpression(visitor, context,
+        Expression windowLowerBoundary = parseIntToExpression(visitor, context,
                 Math.negateExact(dataPoints - 1));
         //window definition
         visitor.analyze(sortField, context);
@@ -123,15 +132,15 @@ private static NamedExpression getWMAComputationExpression(CatalystExpressionVis
                 SortUtils.isSortedAscending(sortField),
                 windowLowerBoundary);
         // Divisor
-        Expression divisor = getIntExpression(visitor, context,
+        Expression divisor = parseIntToExpression(visitor, context,
                 (dataPoints * (dataPoints + 1) / 2));
         // Aggregation
-        Expression WMAExpression = getNthValueAggregations(visitor, node, context, windowDefinition, dataPoints)
+        Expression wmaExpression = getNthValueAggregations(visitor, node, context, windowDefinition, dataPoints)
                         .stream()
                         .reduce(Add::new)
                         .orElse(null);
 
-        return getAlias(node.getAlias(), new Divide(WMAExpression, divisor));
+        return getAlias(node.getAlias(), new Divide(wmaExpression, divisor));
     }
 
     /**
@@ -156,7 +165,7 @@ private static NamedExpression getAlias(String name, Expression expression) {
      * @param i Target value for the expression.
      * @return An expression object which contain integer value i.
      */
-    static Expression getIntExpression(CatalystExpressionVisitor expressionVisitor, CatalystPlanContext context,  int i) {
+    static Expression parseIntToExpression(CatalystExpressionVisitor expressionVisitor, CatalystPlanContext context, int i) {
         expressionVisitor.visitLiteral(new Literal(i,
                 DataType.INTEGER), context);
         return context.popNamedParseExpressions().get();
@@ -198,7 +207,7 @@ private static List<Expression> getNthValueAggregations(CatalystExpressionVisito
         List<Expression> expressions = new ArrayList<>();
         for (int i = 1; i <= dataPoints; i++) {
             // Get the offset parameter
-            Expression offSetExpression = getIntExpression(visitor, context, i);
+            Expression offSetExpression = parseIntToExpression(visitor, context, i);
 
             // Composite the nth_value expression.
             Function func =  new Function(BuiltinFunctionName.NTH_VALUE.name(),