/*
 Copyright (c) 2007, Distributed Computing Group (DCG)
                    ETH Zurich
                    Switzerland
                    dcg.ethz.ch

 All rights reserved.

 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions
 are met:

 - Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.

 - Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   documentation and/or other materials provided with the
   distribution.

 - Neither the name 'Sinalgo' nor the names of its contributors may be
   used to endorse or promote products derived from this software
   without specific prior written permission.

 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package sinalgo.nodes.edges;

/**
 * This is an implementation of a bidirectional edge. Actually it is not a bidirectional edge
 * but it is a unidirectional edge that gaurantees that the edge in the opposite direction 
 * exists as well.
 */
public class BidirectionalEdge extends Edge{
	
	/* (non-Javadoc)
	 * @see sinalgo.nodes.edges.Edge#initializeEdge()
	 */
	public void initializeEdge(){
		if(oppositeEdge == null){
			//this is a hack to ensure that this edge is already in the outgoing ot the start node. Otherwise the two edges would 
			//end in an infinite loop
			startNode.outgoingConnections.hackyAppend(this);
			
			endNode.outgoingConnections.add(endNode, startNode, true);
			findOppositeEdge();
		}
	}
	
	@Override
	public void cleanUp() {
		if(this.oppositeEdge != null){
			//there is a related edge to this one.
			Edge oe = this.oppositeEdge;
			this.oppositeEdge = null;
			oe.oppositeEdge = null; // set unlink oppositeEdges to avoid loops
			this.endNode.outgoingConnections.remove(this.endNode, this.startNode); // remove the opposite edge
			oe.free();
		}
	}
}
