/*
 * 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 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.expressions.AbstractFunctionCallExpression;
import edu.uci.ics.hyracks.algebricks.core.algebra.expressions.ScalarFunctionCallExpression;
import edu.uci.ics.hyracks.algebricks.core.algebra.functions.AlgebricksBuiltinFunctions;
import edu.uci.ics.hyracks.algebricks.core.algebra.functions.IFunctionInfo;
import edu.uci.ics.hyracks.algebricks.core.algebra.operators.logical.AbstractLogicalOperator;
import edu.uci.ics.hyracks.algebricks.core.algebra.operators.logical.SelectOperator;
import edu.uci.ics.hyracks.algebricks.core.rewriter.base.IAlgebraicRewriteRule;

/**
 * Matches the following operator pattern:
 * (select) <-- ((assign)* <-- (select)*)+
 * 
 * Consolidates the selects to:
 * (select) <-- (assign)*
 *
 */
public class ConsolidateSelectsRule implements IAlgebraicRewriteRule {

    @Override
    public boolean rewritePost(Mutable<ILogicalOperator> opRef, IOptimizationContext context) {
        return false;
    }

    @Override
    public boolean rewritePre(Mutable<ILogicalOperator> opRef, IOptimizationContext context) throws AlgebricksException {
    	AbstractLogicalOperator op = (AbstractLogicalOperator) opRef.getValue();
        if (op.getOperatorTag() != LogicalOperatorTag.SELECT) {
            return false;
        }
        SelectOperator firstSelect = (SelectOperator) op;

        IFunctionInfo andFn = context.getMetadataProvider().lookupFunction(AlgebricksBuiltinFunctions.AND);
        // New conjuncts for consolidated select.
        AbstractFunctionCallExpression conj = null;        
        AbstractLogicalOperator topMostOp = null;
        AbstractLogicalOperator selectParent = null;
        AbstractLogicalOperator nextSelect = firstSelect;
		do {
        	// Skip through assigns.
            do {
            	selectParent = nextSelect;
            	nextSelect = (AbstractLogicalOperator) selectParent.getInputs().get(0).getValue();
            } while (nextSelect.getOperatorTag() == LogicalOperatorTag.ASSIGN);
            // Stop if the child op is not a select.
            if (nextSelect.getOperatorTag() != LogicalOperatorTag.SELECT) {
        		break;
        	}
            // Remember the top-most op that we are not removing.
            topMostOp = selectParent;
            
            // Initialize the new conjuncts, if necessary.
            if (conj == null) {
            	conj = new ScalarFunctionCallExpression(andFn);
            	// Add the first select's condition.
            	conj.getArguments().add(new MutableObject<ILogicalExpression>(firstSelect.getCondition().getValue()));
            }
            
            // Consolidate all following selects.
            do {
                // Add the condition nextSelect to the new list of conjuncts.
                conj.getArguments().add(((SelectOperator) nextSelect).getCondition());
                selectParent = nextSelect;
                nextSelect = (AbstractLogicalOperator) nextSelect.getInputs().get(0).getValue();
            } while (nextSelect.getOperatorTag() == LogicalOperatorTag.SELECT);
            
            // Hook up the input of the top-most remaining op if necessary.
            if (topMostOp.getOperatorTag() == LogicalOperatorTag.ASSIGN || topMostOp == firstSelect) {
            	topMostOp.getInputs().set(0, selectParent.getInputs().get(0));
            }
            
            // Prepare for next iteration.
            nextSelect = selectParent;
        } while (true);
		
		// Did we consolidate any selects?
        if (conj == null) {
        	return false;
        }
        
        // Set the new conjuncts.
        firstSelect.getCondition().setValue(conj);
        context.computeAndSetTypeEnvironmentForOperator(firstSelect);
        return true;
    }
}