/**
    * Copyright (c) 2008, The JUNG Authors 
    *
    * All rights reserved.
    *
    * This software is open-source under the BSD license; see either
    * "license.txt" or
    * https://github.com/jrtom/jung/blob/master/LICENSE for a description.
    * Created on Jul 14, 2008
   * 
   */
  package edu.uci.ics.jung.algorithms.scoring.util;
  
  import com.google.common.base.Function;
  
  import edu.uci.ics.jung.graph.Hypergraph;
  import edu.uci.ics.jung.graph.util.EdgeType;
  
  /**
   * An edge weight function that assigns weights as uniform
   * transition probabilities.
   * For undirected edges, returns 1/degree(v) (where 'v' is the
   * vertex in the VEPair.
   * For directed edges, returns 1/outdegree(source(e)) (where 'e'
   * is the edge in the VEPair).
   * Throws an <code>IllegalArgumentException</code> if the input 
   * edge is neither EdgeType.UNDIRECTED nor EdgeType.DIRECTED.
   *
   */
  public class UniformDegreeWeight<V, E> implements
  		Function<VEPair<V, E>, Double> 
  {
      private Hypergraph<V, E> graph;
      
      /**
       * @param graph the graph for which an instance is being created
       */
      public UniformDegreeWeight(Hypergraph<V, E> graph)
      {
          this.graph = graph;
      }
  
  	public Double apply(VEPair<V, E> ve_pair) 
  	{
  		E e = ve_pair.getE();
  		V v = ve_pair.getV();
  		EdgeType edge_type = graph.getEdgeType(e);
  		if (edge_type == EdgeType.UNDIRECTED)
  			return 1.0 / graph.degree(v);
  		if (edge_type == EdgeType.DIRECTED)
  			return 1.0 / graph.outDegree(graph.getSource(e));
  		throw new IllegalArgumentException("can't handle edge type: " + edge_type);
  	}
  
  }