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.runtime.aggregates.collections;
  
  import org.apache.asterix.runtime.aggregates.std.AbstractAggregateFunction;
  import org.apache.asterix.runtime.evaluators.functions.PointableHelper;
  import org.apache.hyracks.algebricks.runtime.base.IAggregateEvaluator;
  import org.apache.hyracks.algebricks.runtime.base.IAggregateEvaluatorFactory;
  import org.apache.hyracks.algebricks.runtime.base.IScalarEvaluator;
  import org.apache.hyracks.algebricks.runtime.base.IScalarEvaluatorFactory;
  import org.apache.hyracks.api.context.IEvaluatorContext;
  import org.apache.hyracks.api.exceptions.HyracksDataException;
  import org.apache.hyracks.api.exceptions.SourceLocation;
  import org.apache.hyracks.data.std.api.IPointable;
  import org.apache.hyracks.data.std.primitive.VoidPointable;
  import org.apache.hyracks.data.std.util.ArrayBackedValueStorage;
  import org.apache.hyracks.dataflow.common.data.accessors.IFrameTupleReference;
  
  class LastElementEvalFactory implements IAggregateEvaluatorFactory {
  
      private static final long serialVersionUID = 1L;
      private final IScalarEvaluatorFactory[] args;
      private final SourceLocation sourceLoc;
  
      LastElementEvalFactory(IScalarEvaluatorFactory[] args, SourceLocation sourceLoc) {
          this.args = args;
          this.sourceLoc = sourceLoc;
      }
  
      @Override
      public IAggregateEvaluator createAggregateEvaluator(final IEvaluatorContext ctx) throws HyracksDataException {
          return new AbstractAggregateFunction(sourceLoc) {
  
              // Needs to copy the bytes from inputVal to outputVal because the byte space of inputVal could be re-used
              // by consequent tuples.
              private ArrayBackedValueStorage outputVal = new ArrayBackedValueStorage();
              private IPointable inputVal = new VoidPointable();
              private IScalarEvaluator eval = args[0].createScalarEvaluator(ctx);
              private boolean empty;
  
              @Override
              public void init() {
                  empty = true;
              }
  
              @Override
              public void step(IFrameTupleReference tuple) throws HyracksDataException {
                  eval.evaluate(tuple, inputVal);
                  outputVal.assign(inputVal);
                  empty = false;
              }
  
              @Override
              public void finish(IPointable result) {
                  if (empty) {
                      PointableHelper.setNull(result);
                  } else {
                      result.set(outputVal);
                  }
              }
  
              @Override
              public void finishPartial(IPointable result) {
                  throw new UnsupportedOperationException();
              }
          };
      }
  
  }
  