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/***********************************************************************************************************************
 * Copyright (C) 2010-2013 by the Stratosphere project (http://stratosphere.eu)
 *
 * 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 eu.stratosphere.compiler.dag;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import eu.stratosphere.compiler.CompilerException;
import eu.stratosphere.compiler.DataStatistics;
import eu.stratosphere.compiler.operators.OperatorDescriptorDual;
import eu.stratosphere.compiler.operators.UtilSinkJoinOpDescriptor;
import eu.stratosphere.compiler.util.NoOpBinaryUdfOp;

/**
 * This class represents a utility node that is not part of the actual plan. It is used for plans with multiple data sinks to
 * transform it into a plan with a single root node. That way, the code that makes sure no costs are double-counted and that 
 * candidate selection works correctly with nodes that have multiple outputs is transparently reused.
 */
public class SinkJoiner extends TwoInputNode {
	
	public SinkJoiner(OptimizerNode input1, OptimizerNode input2) {
		super(NoOpBinaryUdfOp.INSTANCE);

		PactConnection conn1 = new PactConnection(input1, this);
		PactConnection conn2 = new PactConnection(input2, this);
		
		this.input1 = conn1;
		this.input2 = conn2;
		
		setDegreeOfParallelism(1);
		setSubtasksPerInstance(1);
	}
	
	@Override
	public String getName() {
		return "Internal Utility Node";
	}
	
	@Override
	public List getOutgoingConnections() {
		return Collections.emptyList();
	}
	
	@Override
	public void computeUnclosedBranchStack() {
		if (this.openBranches != null) {
			return;
		}
		
		addClosedBranches(getFirstPredecessorNode().closedBranchingNodes);
		addClosedBranches(getSecondPredecessorNode().closedBranchingNodes);
		
		List pred1branches = getFirstPredecessorNode().openBranches;
		List pred2branches = getSecondPredecessorNode().openBranches;
		
		// if the predecessors do not have branches, then we have multiple sinks that do not originate from
		// a common data flow.
		if (pred1branches == null || pred1branches.isEmpty() || pred2branches == null || pred2branches.isEmpty()) {
			throw new CompilerException("The given program contains multiple disconnected data flows.");
		}
		
		// copy the lists and merge
		List result1 = new ArrayList(pred1branches);
		List result2 = new ArrayList(pred2branches);
		
		ArrayList result = new ArrayList();
		mergeLists(result1, result2, result);
		
//		if (!didCloseSomeBranch) {
//			// if the sink joiners do not close branches, then we have disjoint data flows.
//			throw new CompilerException("The given program contains multiple disconnected data flows.");
//		}
		
		this.openBranches = result.isEmpty() ? Collections.emptyList() : result;
	}

	@Override
	protected List getPossibleProperties() {
		return Collections.singletonList(new UtilSinkJoinOpDescriptor());
	}

	@Override
	public void computeOutputEstimates(DataStatistics statistics) {
		// nothing to be done here
	}

	@Override
	protected void computeOperatorSpecificDefaultEstimates(DataStatistics statistics) {
		// no estimates needed at this point
	}
}