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.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.common.utils.Pair;
  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.VariableReferenceExpression;
  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.algebra.operators.logical.visitors.VariableUtilities;
  import org.apache.hyracks.algebricks.core.rewriter.base.IAlgebraicRewriteRule;
  
  /**
   * This rule is to inline unnest functions that are hold by variables.
   * This rule is to fix issue 201.
   */
  public class InlineUnnestFunctionRule 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 op1 = (AbstractLogicalOperator) opRef.getValue();
          if (context.checkIfInDontApplySet(this, op1)) {
              return false;
          }
          context.addToDontApplySet(this, op1);
          if (op1.getOperatorTag() != LogicalOperatorTag.UNNEST) {
              return false;
          }
          UnnestOperator unnestOperator = (UnnestOperator) op1;
          AbstractFunctionCallExpression expr =
                  (AbstractFunctionCallExpression) unnestOperator.getExpressionRef().getValue();
          // we only inline for the scan-collection function
          if (expr.getFunctionIdentifier() != BuiltinFunctions.SCAN_COLLECTION) {
              return false;
          }
  
          // inline all variables from an unnesting function call
          List<Mutable<ILogicalExpression>> args = expr.getArguments();
          boolean changed = false;
          for (int i = 0; i < args.size(); i++) {
              ILogicalExpression argExpr = args.get(i).getValue();
              if (argExpr.getExpressionTag() == LogicalExpressionTag.VARIABLE) {
                  VariableReferenceExpression varExpr = (VariableReferenceExpression) argExpr;
                  changed |= inlineVariable(varExpr.getVariableReference(), unnestOperator);
              }
          }
          return changed;
      }
  
      /**
       * This method is to inline one variable
       *
       * @param usedVar
       *            A variable that is used by the scan-collection function in the unnest operator
       * @param unnestOp
       *            The unnest operator.
       * @throws AlgebricksException
       */
      private boolean inlineVariable(LogicalVariable usedVar, UnnestOperator unnestOp) throws AlgebricksException {
          AbstractFunctionCallExpression expr = (AbstractFunctionCallExpression) unnestOp.getExpressionRef().getValue();
          List<Pair<AbstractFunctionCallExpression, Integer>> parentAndIndexList = new ArrayList<>();
          getParentFunctionExpression(usedVar, expr, parentAndIndexList);
          ILogicalExpression usedVarOrginExpr =
                  findUsedVarOrigin(usedVar, unnestOp, (AbstractLogicalOperator) unnestOp.getInputs().get(0).getValue());
          if (usedVarOrginExpr != null) {
              for (Pair<AbstractFunctionCallExpression, Integer> parentAndIndex : parentAndIndexList) {
                  // we only rewrite the top scan-collection function
                  if (parentAndIndex.first.getFunctionIdentifier() == BuiltinFunctions.SCAN_COLLECTION
                          && parentAndIndex.first == expr) {
                      unnestOp.getExpressionRef().setValue(usedVarOrginExpr);
                  }
              }
              return true;
          }
          return false;
      }
  
      private void getParentFunctionExpression(LogicalVariable usedVar, AbstractFunctionCallExpression funcExpr,
              List<Pair<AbstractFunctionCallExpression, Integer>> parentAndIndexList) {
          List<Mutable<ILogicalExpression>> args = funcExpr.getArguments();
          for (int i = 0; i < args.size(); i++) {
              ILogicalExpression argExpr = args.get(i).getValue();
              if (argExpr.getExpressionTag() == LogicalExpressionTag.VARIABLE) {
                  VariableReferenceExpression varExpr = (VariableReferenceExpression) argExpr;
                  if (varExpr.getVariableReference().equals(usedVar)) {
                      parentAndIndexList.add(new Pair<>(funcExpr, i));
                  }
              }
              if (argExpr.getExpressionTag() == LogicalExpressionTag.FUNCTION_CALL) {
                  getParentFunctionExpression(usedVar, (AbstractFunctionCallExpression) argExpr, parentAndIndexList);
              }
          }
      }
  
      private ILogicalExpression findUsedVarOrigin(LogicalVariable usedVar, AbstractLogicalOperator parentOp,
              AbstractLogicalOperator currentOp) throws AlgebricksException {
          ILogicalExpression ret = null;
          if (currentOp.getOperatorTag() == LogicalOperatorTag.ASSIGN) {
              List<LogicalVariable> producedVars = new ArrayList<>();
              VariableUtilities.getProducedVariables(currentOp, producedVars);
              if (producedVars.contains(usedVar)) {
                  AssignOperator assignOp = (AssignOperator) currentOp;
                  int index = assignOp.getVariables().indexOf(usedVar);
                  ILogicalExpression returnedExpr = assignOp.getExpressions().get(index).getValue();
                  if (returnedExpr.getExpressionTag() == LogicalExpressionTag.FUNCTION_CALL) {
                      AbstractFunctionCallExpression funcExpr = (AbstractFunctionCallExpression) returnedExpr;
                      if (BuiltinFunctions.isBuiltinUnnestingFunction(funcExpr.getFunctionIdentifier())) {
                          // we only inline for unnest functions
                          removeUnecessaryAssign(parentOp, currentOp, assignOp, index);
                          ret = returnedExpr;
                      }
                  } else if (returnedExpr.getExpressionTag() == LogicalExpressionTag.VARIABLE) {
                      // recursively inline
                      VariableReferenceExpression varExpr = (VariableReferenceExpression) returnedExpr;
                      LogicalVariable var = varExpr.getVariableReference();
                      ILogicalExpression finalExpr = findUsedVarOrigin(var, currentOp,
                              (AbstractLogicalOperator) currentOp.getInputs().get(0).getValue());
                      if (finalExpr != null) {
                          removeUnecessaryAssign(parentOp, currentOp, assignOp, index);
                          ret = finalExpr;
                      }
                  }
              }
          } else {
              for (Mutable<ILogicalOperator> child : currentOp.getInputs()) {
                  ILogicalExpression expr =
                          findUsedVarOrigin(usedVar, currentOp, (AbstractLogicalOperator) child.getValue());
                  if (expr != null) {
                      ret = expr;
                  }
              }
          }
          return ret;
      }
  
      private void removeUnecessaryAssign(AbstractLogicalOperator parentOp, AbstractLogicalOperator currentOp,
              AssignOperator assignOp, int index) {
          // TODO: how come the assign variable is removed before checking that other operators might be using it?
          assignOp.getVariables().remove(index);
          assignOp.getExpressions().remove(index);
          if (assignOp.getVariables().size() == 0) {
              int opIndex = parentOp.getInputs().indexOf(new MutableObject<ILogicalOperator>(currentOp));
              parentOp.getInputs().get(opIndex).setValue(assignOp.getInputs().get(0).getValue());
          }
      }
  }
  