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.ArrayList;
  import java.util.List;
  
  import org.apache.asterix.lang.common.util.FunctionUtil;
  import org.apache.asterix.om.functions.BuiltinFunctions;
  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.AbstractFunctionCallExpression.FunctionKind;
  import org.apache.hyracks.algebricks.core.algebra.expressions.UnnestingFunctionCallExpression;
  import org.apache.hyracks.algebricks.core.algebra.expressions.VariableReferenceExpression;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.AbstractAssignOperator;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.AbstractLogicalOperator;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.UnnestOperator;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.visitors.VariableUtilities;
  import org.apache.hyracks.algebricks.core.rewriter.base.IAlgebraicRewriteRule;
  
  public class FeedScanCollectionToUnnest implements IAlgebraicRewriteRule {
  
      @Override
      public boolean rewritePre(Mutable<ILogicalOperator> opRef, IOptimizationContext context) {
          return false;
      }
  
      @Override
      public boolean rewritePost(Mutable<ILogicalOperator> opRef, IOptimizationContext context)
              throws AlgebricksException {
          AbstractLogicalOperator op = (AbstractLogicalOperator) opRef.getValue();
          if (context.checkIfInDontApplySet(this, op)) {
              return false;
          }
          if (op.getOperatorTag() != LogicalOperatorTag.UNNEST) {
              context.addToDontApplySet(this, op);
              return false;
          }
          UnnestOperator unnest = (UnnestOperator) op;
          ILogicalExpression unnestExpr = unnest.getExpressionRef().getValue();
          if (needsScanCollection(unnestExpr, op)) {
              UnnestingFunctionCallExpression newExpr =
                      new UnnestingFunctionCallExpression(FunctionUtil.getFunctionInfo(BuiltinFunctions.SCAN_COLLECTION),
                              new MutableObject<ILogicalExpression>(unnestExpr));
              newExpr.setSourceLocation(unnestExpr.getSourceLocation());
              unnest.getExpressionRef().setValue(newExpr);
              context.addToDontApplySet(this, op);
              return true;
          }
          context.addToDontApplySet(this, op);
          return false;
      }
  
      private ILogicalExpression findVarOriginExpression(LogicalVariable v, ILogicalOperator op)
              throws AlgebricksException {
          boolean searchInputs = false;
          if (!(op instanceof AbstractAssignOperator)) {
              searchInputs = true;
          } else {
              AbstractAssignOperator aao = (AbstractAssignOperator) op;
              List<LogicalVariable> producedVars = new ArrayList<>();
              VariableUtilities.getProducedVariables(op, producedVars);
              int exprIndex = producedVars.indexOf(v);
              if (exprIndex == -1) {
                  searchInputs = true;
              } else {
                  ILogicalExpression originalCandidate = aao.getExpressions().get(exprIndex).getValue();
                  if (originalCandidate.getExpressionTag() == LogicalExpressionTag.VARIABLE) {
                      searchInputs = true;
                  } else {
                      return originalCandidate;
                  }
              }
          }
  
          if (searchInputs) {
              for (Mutable<ILogicalOperator> childOp : op.getInputs()) {
                  ILogicalExpression ret = findVarOriginExpression(v, childOp.getValue());
                  if (ret != null) {
                      return ret;
                  }
              }
          }
  
          throw new IllegalStateException("Unable to find the original expression that produced variable " + v);
      }
  
      private boolean needsScanCollection(ILogicalExpression unnestExpr, ILogicalOperator op) throws AlgebricksException {
          switch (unnestExpr.getExpressionTag()) {
              case VARIABLE: {
                  LogicalVariable v = ((VariableReferenceExpression) unnestExpr).getVariableReference();
                  ILogicalExpression originalExpr = findVarOriginExpression(v, op);
                  if (originalExpr.getExpressionTag() == LogicalExpressionTag.CONSTANT) {
                      return false;
                  } else {
                      return !isUnnestingFunction(originalExpr);
                  }
              }
              case FUNCTION_CALL: {
                  return !isUnnestingFunction(unnestExpr);
              }
              default: {
                  return false;
              }
          }
      }
  
      private boolean isUnnestingFunction(ILogicalExpression expr) {
          if (expr.getExpressionTag() == LogicalExpressionTag.FUNCTION_CALL) {
              AbstractFunctionCallExpression fce = (AbstractFunctionCallExpression) expr;
              return fce.getKind() == FunctionKind.UNNEST;
          }
          return false;
      }
  }
  