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.lang.common.util.FunctionUtil;
  import org.apache.asterix.om.functions.BuiltinFunctions;
  import org.apache.asterix.om.types.IAType;
  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.ILogicalExpression;
  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.LogicalExpressionTag;
  import org.apache.hyracks.algebricks.core.algebra.base.LogicalOperatorTag;
  import org.apache.hyracks.algebricks.core.algebra.base.LogicalVariable;
  import org.apache.hyracks.algebricks.core.algebra.expressions.AbstractFunctionCallExpression;
  import org.apache.hyracks.algebricks.core.algebra.expressions.IVariableTypeEnvironment;
  import org.apache.hyracks.algebricks.core.algebra.expressions.UnnestingFunctionCallExpression;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.AbstractLogicalOperator;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.AssignOperator;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.UnnestOperator;
  import org.apache.hyracks.algebricks.core.rewriter.base.IAlgebraicRewriteRule;
  
  /**
   * This rule introduces a unnest operator for the collection-to-sequence function (if the input to the function is a collection).
   *
   * @author yingyib
   */
  public class IntroduceUnnestForCollectionToSequenceRule implements IAlgebraicRewriteRule {
  
      @Override
      public boolean rewritePre(Mutable<ILogicalOperator> opRef, IOptimizationContext context)
              throws AlgebricksException {
          return false;
      }
  
      @Override
      public boolean rewritePost(Mutable<ILogicalOperator> opRef, IOptimizationContext context)
              throws AlgebricksException {
          AbstractLogicalOperator op = (AbstractLogicalOperator) opRef.getValue();
          if (op.getOperatorTag() != LogicalOperatorTag.ASSIGN) {
              return false;
          }
          AssignOperator assign = (AssignOperator) op;
          List<Mutable<ILogicalExpression>> exprs = assign.getExpressions();
          if (exprs.size() != 1) {
              return false;
          }
          ILogicalExpression expr = exprs.get(0).getValue();
          if (expr.getExpressionTag() != LogicalExpressionTag.FUNCTION_CALL) {
              return false;
          }
          AbstractFunctionCallExpression func = (AbstractFunctionCallExpression) expr;
          if (func.getFunctionIdentifier() != BuiltinFunctions.COLLECTION_TO_SEQUENCE) {
              return false;
          }
  
          IVariableTypeEnvironment env = assign.computeInputTypeEnvironment(context);
          ILogicalExpression argExpr = func.getArguments().get(0).getValue();
          IAType outerExprType = (IAType) env.getType(expr);
          IAType innerExprType = (IAType) env.getType(argExpr);
          if (outerExprType.equals(innerExprType)) {
              /** nothing is changed with the collection-to-sequence function, remove the collection-sequence function call */
              assign.getExpressions().set(0, new MutableObject<ILogicalExpression>(argExpr));
              return true;
          }
          /** change the assign operator to an unnest operator */
          LogicalVariable var = assign.getVariables().get(0);
          UnnestingFunctionCallExpression scanCollExpr =
                  new UnnestingFunctionCallExpression(FunctionUtil.getFunctionInfo(BuiltinFunctions.SCAN_COLLECTION),
                          new MutableObject<ILogicalExpression>(argExpr));
          scanCollExpr.setSourceLocation(func.getSourceLocation());
          @SuppressWarnings("unchecked")
          UnnestOperator unnest = new UnnestOperator(var, new MutableObject<ILogicalExpression>(scanCollExpr));
          unnest.setSourceLocation(assign.getSourceLocation());
          unnest.getInputs().addAll(assign.getInputs());
          opRef.setValue(unnest);
          context.computeAndSetTypeEnvironmentForOperator(unnest);
          return true;
      }
  }
  