content: /*
   * 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.asterix.optimizer.rules;
  
  import java.util.List;
  
  import org.apache.asterix.om.functions.BuiltinFunctions;
  import org.apache.commons.lang3.mutable.Mutable;
  import org.apache.hyracks.algebricks.core.algebra.base.ILogicalExpression;
  import org.apache.hyracks.algebricks.core.algebra.base.LogicalExpressionTag;
  import org.apache.hyracks.algebricks.core.algebra.expressions.AbstractFunctionCallExpression;
  import org.apache.hyracks.algebricks.core.algebra.functions.FunctionIdentifier;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.AggregateOperator;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.WindowOperator;
  import org.apache.hyracks.algebricks.rewriter.rules.ConsolidateWindowOperatorsRule;
  
  /**
   * Asterix-specific rule that enables consolidation of window operators in the following additional cases
   * <ul>
   * <li> Different {@link WindowOperator#getFrameMaxObjects()} values if aggregate function is
   *      {@link BuiltinFunctions#FIRST_ELEMENT}
   * </li>
   * </ul>
   */
  public final class AsterixConsolidateWindowOperatorsRule extends ConsolidateWindowOperatorsRule {
  
      @Override
      protected boolean subsumeFrameMaxObjects(int maxObjects1, int maxObjects2, AggregateOperator aggOp2) {
          if (allFunctionCalls(aggOp2.getExpressions(), BuiltinFunctions.FIRST_ELEMENT) && maxObjects2 >= 1
                  && (maxObjects1 == WindowOperator.FRAME_MAX_OBJECTS_UNLIMITED || maxObjects1 >= maxObjects2)) {
              return true;
          }
          return super.subsumeFrameMaxObjects(maxObjects1, maxObjects2, aggOp2);
      }
  
      private boolean allFunctionCalls(List<Mutable<ILogicalExpression>> exprRefs, FunctionIdentifier fid) {
          for (Mutable<ILogicalExpression> exprRef : exprRefs) {
              ILogicalExpression expr = exprRef.getValue();
              if (expr.getExpressionTag() != LogicalExpressionTag.FUNCTION_CALL) {
                  return false;
              }
              AbstractFunctionCallExpression callExpr = (AbstractFunctionCallExpression) expr;
              if (!callExpr.getFunctionIdentifier().equals(fid)) {
                  return false;
              }
          }
          return true;
      }
  }
  