/**
 * (C) Copyright IBM Corp. 2010, 2015
 *
 * 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 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 com.ibm.bi.dml.hops.rewrite;

import java.util.ArrayList;

import com.ibm.bi.dml.hops.Hop;
import com.ibm.bi.dml.hops.HopsException;
import com.ibm.bi.dml.hops.LiteralOp;
import com.ibm.bi.dml.parser.IfStatement;
import com.ibm.bi.dml.parser.IfStatementBlock;
import com.ibm.bi.dml.parser.StatementBlock;

/**
 * Rule: Simplify program structure by pulling if or else statement body out
 * (removing the if statement block ifself) in order to allow intra-procedure
 * analysis to propagate exact statistics.
 * 
 */
public class RewriteRemoveUnnecessaryBranches extends StatementBlockRewriteRule
{

	@Override
	public ArrayList<StatementBlock> rewriteStatementBlock(StatementBlock sb, ProgramRewriteStatus state)
		throws HopsException 
	{
		ArrayList<StatementBlock> ret = new ArrayList<StatementBlock>();
		
		if( sb instanceof IfStatementBlock )
		{
			IfStatementBlock isb = (IfStatementBlock) sb;
			Hop pred = isb.getPredicateHops();
			
			//apply rewrite if literal op (constant value)
			if( pred instanceof LiteralOp )
			{
				IfStatement istmt = (IfStatement)isb.getStatement(0);
				LiteralOp litpred = (LiteralOp) pred;
				boolean condition = HopRewriteUtils.getBooleanValue(litpred);
				
				if( condition )
				{
					//pull-out simple if body
					if( !istmt.getIfBody().isEmpty() )
						ret.addAll( istmt.getIfBody() ); //pull if-branch
					//otherwise: add nothing (remove if-else)
				}
				else
				{
					//pull-out simple else body
					if( !istmt.getElseBody().isEmpty() )
						ret.addAll( istmt.getElseBody() ); //pull else-branch
					//otherwise: add nothing (remove if-else)
				}
				
				state.setRemovedBranches();
				LOG.debug("Applied removeUnnecessaryBranches (lines "+sb.getBeginLine()+"-"+sb.getEndLine()+").");
			}
			else //keep original sb (non-constant condition)
				ret.add( sb );
		}
		else //keep original sb (no if)
			ret.add( sb );
		
		return ret;
	}
}