/*
 * Copyright 2009-2010 by The Regents of the University of California
 * Licensed 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 from
 * 
 *     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 edu.uci.ics.hyracks.algebricks.rewriter.rules;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import org.apache.commons.lang3.mutable.Mutable;
import org.apache.commons.lang3.mutable.MutableObject;

import edu.uci.ics.hyracks.algebricks.common.exceptions.AlgebricksException;
import edu.uci.ics.hyracks.algebricks.core.algebra.base.ILogicalExpression;
import edu.uci.ics.hyracks.algebricks.core.algebra.base.ILogicalOperator;
import edu.uci.ics.hyracks.algebricks.core.algebra.base.IOptimizationContext;
import edu.uci.ics.hyracks.algebricks.core.algebra.base.LogicalOperatorTag;
import edu.uci.ics.hyracks.algebricks.core.algebra.base.LogicalVariable;
import edu.uci.ics.hyracks.algebricks.core.algebra.expressions.ConstantExpression;
import edu.uci.ics.hyracks.algebricks.core.algebra.operators.logical.AbstractLogicalOperator;
import edu.uci.ics.hyracks.algebricks.core.algebra.operators.logical.AbstractScanOperator;
import edu.uci.ics.hyracks.algebricks.core.algebra.operators.logical.EmptyTupleSourceOperator;
import edu.uci.ics.hyracks.algebricks.core.algebra.operators.logical.InnerJoinOperator;
import edu.uci.ics.hyracks.algebricks.core.algebra.operators.logical.visitors.VariableUtilities;
import edu.uci.ics.hyracks.algebricks.core.rewriter.base.IAlgebraicRewriteRule;

public class SimpleUnnestToProductRule 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 (op.getOperatorTag() != LogicalOperatorTag.DATASOURCESCAN
                && op.getOperatorTag() != LogicalOperatorTag.UNNEST) {
            return false;
        }

        Mutable<ILogicalOperator> opRef2 = op.getInputs().get(0);
        AbstractLogicalOperator op2 = (AbstractLogicalOperator) opRef2.getValue();

        if (!(op2 instanceof AbstractScanOperator) && !descOrSelfIsSourceScan(op2)) {
            return false;
        }
        // Make sure that op does not use any variables produced by op2.
        if (!opsAreIndependent(op, op2)) {
            return false;
        }

        InnerJoinOperator product = new InnerJoinOperator(
                new MutableObject<ILogicalExpression>(ConstantExpression.TRUE));

        EmptyTupleSourceOperator ets = new EmptyTupleSourceOperator();
        context.computeAndSetTypeEnvironmentForOperator(ets);
        Mutable<ILogicalOperator> emptySrc = new MutableObject<ILogicalOperator>(ets);
        List<Mutable<ILogicalOperator>> opInpList = op.getInputs();
        opInpList.clear();
        opInpList.add(emptySrc);
        product.getInputs().add(opRef2); // outer branch
        product.getInputs().add(new MutableObject<ILogicalOperator>(op));
        opRef.setValue(product); // plug the product in the plan
        context.computeAndSetTypeEnvironmentForOperator(product);
        return true;
    }

    private boolean descOrSelfIsSourceScan(AbstractLogicalOperator op2) {
        // Disregard data source scans in a subplan.
        if (op2.getOperatorTag() == LogicalOperatorTag.SUBPLAN) {
            return false;
        }
        if (op2.getOperatorTag() == LogicalOperatorTag.DATASOURCESCAN
                && op2.getOperatorTag() != LogicalOperatorTag.UNNEST) {
            return true;
        }
        for (Mutable<ILogicalOperator> cRef : op2.getInputs()) {
            AbstractLogicalOperator alo = (AbstractLogicalOperator) cRef.getValue();
            if (descOrSelfIsSourceScan(alo)) {
                return true;
            }
        }
        return false;
    }

    private boolean opsAreIndependent(ILogicalOperator unnestOp, ILogicalOperator outer) throws AlgebricksException {
        List<LogicalVariable> opUsedVars = new ArrayList<LogicalVariable>();
        VariableUtilities.getUsedVariables(unnestOp, opUsedVars);
        Set<LogicalVariable> op2LiveVars = new HashSet<LogicalVariable>();
        VariableUtilities.getLiveVariables(outer, op2LiveVars);
        for (LogicalVariable usedVar : opUsedVars) {
            if (op2LiveVars.contains(usedVar)) {
                return false;
            }
        }
        return true;
    }

}