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   * 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.
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  package org.apache.asterix.optimizer.rules;
  
  import org.apache.asterix.metadata.declared.DataSource;
  import org.apache.asterix.metadata.declared.FeedDataSource;
  import org.apache.asterix.metadata.entities.FeedConnection;
  import org.apache.commons.lang3.mutable.Mutable;
  import org.apache.commons.lang3.mutable.MutableObject;
  import org.apache.hyracks.algebricks.common.exceptions.AlgebricksException;
  import org.apache.hyracks.algebricks.core.algebra.base.ILogicalOperator;
  import org.apache.hyracks.algebricks.core.algebra.base.IOptimizationContext;
  import org.apache.hyracks.algebricks.core.algebra.base.LogicalOperatorTag;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.AbstractLogicalOperator.ExecutionMode;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.AssignOperator;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.DataSourceScanOperator;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.ExchangeOperator;
  import org.apache.hyracks.algebricks.core.algebra.operators.physical.AssignPOperator;
  import org.apache.hyracks.algebricks.core.algebra.operators.physical.RandomPartitionExchangePOperator;
  import org.apache.hyracks.algebricks.core.algebra.properties.DefaultNodeGroupDomain;
  import org.apache.hyracks.algebricks.core.algebra.properties.INodeDomain;
  import org.apache.hyracks.algebricks.core.rewriter.base.IAlgebraicRewriteRule;
  
  public class IntroduceRandomPartitioningFeedComputationRule implements IAlgebraicRewriteRule {
  
      @Override
      public boolean rewritePre(Mutable<ILogicalOperator> opRef, IOptimizationContext context)
              throws AlgebricksException {
          ILogicalOperator op = opRef.getValue();
          if (!op.getOperatorTag().equals(LogicalOperatorTag.ASSIGN)) {
              return false;
          }
  
          ILogicalOperator opChild = op.getInputs().get(0).getValue();
          if (!opChild.getOperatorTag().equals(LogicalOperatorTag.DATASOURCESCAN)) {
              return false;
          }
  
          DataSourceScanOperator scanOp = (DataSourceScanOperator) opChild;
          DataSource dataSource = (DataSource) scanOp.getDataSource();
          if (dataSource.getDatasourceType() != DataSource.Type.FEED) {
              return false;
          }
  
          final FeedDataSource feedDataSource = (FeedDataSource) dataSource;
          FeedConnection feedConnection = feedDataSource.getFeedConnection();
          if (feedConnection.getAppliedFunctions() == null || feedConnection.getAppliedFunctions().size() == 0) {
              return false;
          }
  
          ExchangeOperator exchangeOp = new ExchangeOperator();
          exchangeOp.setSourceLocation(op.getSourceLocation());
          INodeDomain runtimeDomain = feedDataSource.getComputationNodeDomain();
  
          exchangeOp.setPhysicalOperator(new RandomPartitionExchangePOperator(runtimeDomain));
          op.getInputs().get(0).setValue(exchangeOp);
          exchangeOp.getInputs().add(new MutableObject<ILogicalOperator>(scanOp));
          ExecutionMode em = scanOp.getExecutionMode();
          exchangeOp.setExecutionMode(em);
          exchangeOp.computeDeliveredPhysicalProperties(context);
          context.computeAndSetTypeEnvironmentForOperator(exchangeOp);
          exchangeOp.recomputeSchema();
  
          AssignOperator assignOp = (AssignOperator) opRef.getValue();
          AssignPOperator assignPhyOp = (AssignPOperator) assignOp.getPhysicalOperator();
          DefaultNodeGroupDomain computationNode = (DefaultNodeGroupDomain) runtimeDomain;
          String[] nodes = computationNode.getNodes();
          assignPhyOp.setLocationConstraint(nodes);
          return true;
      }
  
      @Override
      public boolean rewritePost(Mutable<ILogicalOperator> opRef, IOptimizationContext context)
              throws AlgebricksException {
          return false;
      }
  
  }
  