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.HashSet;
  import java.util.List;
  import java.util.Objects;
  import java.util.Set;
  
  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.common.utils.Triple;
  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.ILogicalPlan;
  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.IAlgebricksConstantValue;
  import org.apache.hyracks.algebricks.core.algebra.expressions.VariableReferenceExpression;
  import org.apache.hyracks.algebricks.core.algebra.functions.FunctionIdentifier;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.AggregateOperator;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.AssignOperator;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.GroupByOperator;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.LeftOuterJoinOperator;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.LeftOuterUnnestOperator;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.SelectOperator;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.visitors.VariableUtilities;
  import org.apache.hyracks.algebricks.core.algebra.util.OperatorPropertiesUtil;
  import org.apache.hyracks.algebricks.core.rewriter.base.IAlgebraicRewriteRule;
  
  /**
   * This rule cancels left outer unnest on top of a group-by and left-outer join:<br/>
   *
   * <pre>
   * left-outer-unnest $x <- scan-collection($y)
   *   group-by($k){
   *     aggregate $y <- listify($z1)
   *       select not(is-missing/null($z2))
   *         NTS
   *   }
   *     left outer join ($a=$b)
   *       left input branch
   *       right input branch ($z1 and $z2 comes from this branch)
   * </pre>
   *
   * will be converted into<br/>
   *
   * <pre>
   * left outer join ($a=$b)
   *       left input branch
   *       right input branch ($z1 and $z2 comes from this branch)
   * </pre>
   */
  public class RemoveLeftOuterUnnestForLeftOuterJoinRule implements IAlgebraicRewriteRule {
  
      @Override
      public boolean rewritePre(Mutable<ILogicalOperator> opRef, IOptimizationContext context)
              throws AlgebricksException {
          ILogicalOperator op1 = opRef.getValue();
  
          // Checks the plan pattern.
          if (!checkOperatorPattern(op1)) {
              return false;
          }
  
          LeftOuterUnnestOperator outerUnnest = (LeftOuterUnnestOperator) op1;
          GroupByOperator gbyOperator = (GroupByOperator) outerUnnest.getInputs().get(0).getValue();
          LeftOuterJoinOperator lojOperator = (LeftOuterJoinOperator) gbyOperator.getInputs().get(0).getValue();
  
          // Checks whether the left outer unnest and the group-by operator are qualified for rewriting.
          Triple<Boolean, ILogicalExpression, ILogicalExpression> checkGbyResult =
                  checkUnnestAndGby(outerUnnest, gbyOperator, lojOperator);
          // The argument for listify and not(is-missing(...)) check should be variables.
          if (!checkGbyResult.first || checkGbyResult.second == null || !isVariableReference(checkGbyResult.second)
                  || checkGbyResult.third == null || !isVariableReference(checkGbyResult.third)) {
              return false;
          }
  
          // Checks whether both the listify variable and the condition test variable are from the right input
          // branch of the left outer join.
          LogicalVariable listifyVar = ((VariableReferenceExpression) checkGbyResult.second).getVariableReference();
          LogicalVariable conditionTestVar = ((VariableReferenceExpression) checkGbyResult.third).getVariableReference();
          if (!checkListifyAndConditionVar(lojOperator, listifyVar, conditionTestVar)) {
              return false;
          }
  
          // Does the rewrite.
          removeGroupByAndOuterUnnest(opRef, context, outerUnnest, gbyOperator, lojOperator, listifyVar);
          return true;
      }
  
      // Checks the plan pattern.
      private boolean checkOperatorPattern(ILogicalOperator op1) {
          if (op1.getOperatorTag() != LogicalOperatorTag.LEFT_OUTER_UNNEST) {
              return false;
          }
          ILogicalOperator op2 = op1.getInputs().get(0).getValue();
          if (op2.getOperatorTag() != LogicalOperatorTag.GROUP) {
              return false;
          }
          ILogicalOperator op3 = op2.getInputs().get(0).getValue();
          if (op3.getOperatorTag() != LogicalOperatorTag.LEFTOUTERJOIN) {
              return false;
          }
          return true;
      }
  
      // Checks left outer unnest and gby.
      private Triple<Boolean, ILogicalExpression, ILogicalExpression> checkUnnestAndGby(
              LeftOuterUnnestOperator outerUnnest, GroupByOperator gbyOperator, LeftOuterJoinOperator lojOperator) {
          // Checks left outer unnest.
          Pair<Boolean, LogicalVariable> checkUnnestResult = checkUnnest(outerUnnest);
          if (!checkUnnestResult.first) {
              return new Triple<>(false, null, null);
          }
  
          // Checks group-by.
          LogicalVariable varToUnnest = checkUnnestResult.second;
          Triple<Boolean, ILogicalExpression, ILogicalExpression> checkGbyResult =
                  checkGroupBy(gbyOperator, varToUnnest, lojOperator.getMissingValue());
          if (!checkGbyResult.first) {
              return new Triple<>(false, null, null);
          }
          return checkGbyResult;
      }
  
      // Checks whether the left outer unnest operator does not have positional variable and uses
      // only one variable for unnesting.
      private Pair<Boolean, LogicalVariable> checkUnnest(LeftOuterUnnestOperator outerUnnest) {
          if (outerUnnest.getPositionalVariable() != null) {
              return new Pair<>(false, null);
          }
          Set<LogicalVariable> varsToUnnest = new HashSet<>();
          outerUnnest.getExpressionRef().getValue().getUsedVariables(varsToUnnest);
          if (varsToUnnest.size() > 1) {
              return new Pair<>(false, null);
          }
          return new Pair<>(true, varsToUnnest.iterator().next());
      }
  
      // Checks the group-by operator on top of the left outer join operator.
      private Triple<Boolean, ILogicalExpression, ILogicalExpression> checkGroupBy(GroupByOperator gbyOperator,
              LogicalVariable varToUnnest, IAlgebricksConstantValue leftOuterMissingValue) {
          Pair<Boolean, ILogicalOperator> checkNestedPlanResult = checkNestedPlan(gbyOperator);
          if (!checkNestedPlanResult.first) {
              return new Triple<>(false, null, null);
          }
          ILogicalOperator root = checkNestedPlanResult.second;
          if (root.getOperatorTag() != LogicalOperatorTag.AGGREGATE) {
              return new Triple<>(false, null, null);
          }
  
          // Checks aggregate.
          AggregateOperator agg = (AggregateOperator) root;
          Pair<Boolean, ILogicalExpression> listifyArgPair = checksAggregate(agg, varToUnnest);
          if (!listifyArgPair.first) {
              return new Triple<>(false, null, null);
          }
  
          // Checks select.
          ILogicalOperator rootInputOp = root.getInputs().get(0).getValue();
          if (rootInputOp.getOperatorTag() != LogicalOperatorTag.SELECT) {
              return new Triple<>(false, null, null);
          }
          SelectOperator select = (SelectOperator) rootInputOp;
          Pair<Boolean, ILogicalExpression> conditionArgPair = checkSelect(select, leftOuterMissingValue);
          return new Triple<>(true, listifyArgPair.second, conditionArgPair.second);
      }
  
      // Checks the nested plan for the group-by operator.
      private Pair<Boolean, ILogicalOperator> checkNestedPlan(GroupByOperator gbyOperator) {
          List<ILogicalPlan> nestedPlans = gbyOperator.getNestedPlans();
          if (nestedPlans.size() > 1) {
              return new Pair<>(false, null);
          }
          ILogicalPlan plan = nestedPlans.get(0);
          List<Mutable<ILogicalOperator>> roots = plan.getRoots();
          if (roots.size() > 1) {
              return new Pair<>(false, null);
          }
          ILogicalOperator root = roots.get(0).getValue();
          return new Pair<>(true, root);
      }
  
      // Checks the aggregate expression.
      private Pair<Boolean, ILogicalExpression> checksAggregate(AggregateOperator agg, LogicalVariable varToUnnest) {
          if (!agg.getVariables().contains(varToUnnest)) {
              return new Pair<>(false, null);
          }
          List<Mutable<ILogicalExpression>> exprRefs = agg.getExpressions();
          if (exprRefs.size() > 1) {
              return new Pair<>(false, null);
          }
          ILogicalExpression expr = exprRefs.get(0).getValue();
          if (expr.getExpressionTag() != LogicalExpressionTag.FUNCTION_CALL) {
              return new Pair<>(false, null);
          }
          AbstractFunctionCallExpression funcExpr = (AbstractFunctionCallExpression) expr;
          if (!funcExpr.getFunctionIdentifier().equals(BuiltinFunctions.LISTIFY)) {
              return new Pair<>(false, null);
          }
          return new Pair<>(true, funcExpr.getArguments().get(0).getValue());
      }
  
      // Checks the expression for the nested select operator inside the group-by operator.
      private Pair<Boolean, ILogicalExpression> checkSelect(SelectOperator select,
              IAlgebricksConstantValue leftOuterMissingValue) {
          ILogicalExpression condition = select.getCondition().getValue();
          if (condition.getExpressionTag() != LogicalExpressionTag.FUNCTION_CALL) {
              return new Pair<>(false, null);
          }
          AbstractFunctionCallExpression conditionFunc = (AbstractFunctionCallExpression) condition;
          if (!conditionFunc.getFunctionIdentifier().equals(BuiltinFunctions.NOT)) {
              return new Pair<>(false, null);
          }
          condition = conditionFunc.getArguments().get(0).getValue();
          if (condition.getExpressionTag() != LogicalExpressionTag.FUNCTION_CALL) {
              return new Pair<>(false, null);
          }
          conditionFunc = (AbstractFunctionCallExpression) condition;
          FunctionIdentifier isMissingNullFuncId =
                  Objects.requireNonNull(OperatorPropertiesUtil.getIsMissingNullFunction(leftOuterMissingValue));
          if (!conditionFunc.getFunctionIdentifier().equals(isMissingNullFuncId)) {
              return new Pair<>(false, null);
          }
          ILogicalExpression conditionArg = conditionFunc.getArguments().get(0).getValue();
          return new Pair<>(true, conditionArg);
      }
  
      // Checks whether the listify variable and the condition test variable come from the right input
      // branch of the left outer join.
      private boolean checkListifyAndConditionVar(LeftOuterJoinOperator lojOperator, LogicalVariable listifyVar,
              LogicalVariable conditionTestVar) throws AlgebricksException {
          ILogicalOperator rightJoinInputOp = lojOperator.getInputs().get(1).getValue();
          Set<LogicalVariable> rightProducedVars = new HashSet<>();
          VariableUtilities.getLiveVariables(rightJoinInputOp, rightProducedVars);
          if (!rightProducedVars.contains(conditionTestVar) || !rightProducedVars.contains(listifyVar)) {
              return false;
          }
          return true;
      }
  
      // Performs the actual rewrite.
      private void removeGroupByAndOuterUnnest(Mutable<ILogicalOperator> opRef, IOptimizationContext context,
              LeftOuterUnnestOperator outerUnnest, GroupByOperator gbyOperator, LeftOuterJoinOperator lojOperator,
              LogicalVariable listifyVar) throws AlgebricksException {
          List<LogicalVariable> lhs = new ArrayList<>();
          List<Mutable<ILogicalExpression>> rhs = new ArrayList<>();
          lhs.add(outerUnnest.getVariable());
          VariableReferenceExpression listifyVarRef = new VariableReferenceExpression(listifyVar);
          listifyVarRef.setSourceLocation(gbyOperator.getSourceLocation());
          rhs.add(new MutableObject<>(listifyVarRef));
          List<Pair<LogicalVariable, Mutable<ILogicalExpression>>> gbyList = gbyOperator.getGroupByList();
          for (Pair<LogicalVariable, Mutable<ILogicalExpression>> gbyPair : gbyList) {
              lhs.add(gbyPair.first);
              rhs.add(gbyPair.second);
          }
          AssignOperator assignOp = new AssignOperator(lhs, rhs);
          assignOp.setSourceLocation(outerUnnest.getSourceLocation());
          assignOp.getInputs().add(new MutableObject<>(lojOperator));
          lojOperator.setMissingValue(outerUnnest.getMissingValue());
          context.computeAndSetTypeEnvironmentForOperator(lojOperator);
          context.computeAndSetTypeEnvironmentForOperator(assignOp);
          opRef.setValue(assignOp);
      }
  
      private boolean isVariableReference(ILogicalExpression expr) {
          return expr.getExpressionTag() == LogicalExpressionTag.VARIABLE;
      }
  
  }
  