package GraphPackage;
import java.util.Iterator;
/**
   An interface for a vertex in a graph.
   
   @author Frank M. Carrano
   @author Timothy M. Henry
   @version 5.0
*/
public interface VertexInterface<T>
{
   /** Gets this vertex's label.
       @return  The object that labels the vertex. */
   public T getLabel();

   /** Marks this vertex as visited. */
   public void visit();

   /** Removes this vertex's visited mark. */
   public void unvisit();

   /** Sees whether the vertex is marked as visited.
       @return  True if the vertex is visited. */
   public boolean isVisited();

   /** Connects this vertex and a given vertex with a weighted edge.
       The two vertices cannot be the same, and must not already
       have this edge between them. In a directed graph, the edge 
       points toward the given vertex.
       @param endVertex   A vertex in the graph that ends the edge.
       @param edgeWeight  A real-valued edge weight, if any.
       @return  True if the edge is added, or false if not. */
   public boolean connect(VertexInterface<T> endVertex, double edgeWeight);
                         
   /** Connects this vertex and a given vertex with an unweighted 
       edge. The two vertices cannot be the same, and must not 
       already have this edge between them. In a directed graph, 
       the edge points toward the given vertex.
       @param endVertex   A vertex in the graph that ends the edge.
       @return  True if the edge is added, or false if not. */
   public boolean connect(VertexInterface<T> endVertex);

   /** Creates an iterator of this vertex's neighbors by following 
       all edges that begin at this vertex.
       @return  An iterator of the neighboring vertices of this vertex. */
   public Iterator<VertexInterface<T>> getNeighborIterator();

   /** Creates an iterator of the weights of the edges to this 
       vertex's neighbors.
    @return  An iterator of edge weights for edges to neighbors of this
             vertex. */
   public Iterator<Double> getWeightIterator();

   /** Sees whether this vertex has at least one neighbor.
       @return  True if the vertex has a neighbor. */
   public boolean hasNeighbor();

   /** Gets an unvisited neighbor, if any, of this vertex.
       @return  Either a vertex that is an unvisited neighbor or null
                if no such neighbor exists. */
   public VertexInterface<T> getUnvisitedNeighbor();

   /** Records the previous vertex on a path to this vertex.
       @param predecessor  The vertex previous to this one along a path.  */
   public void setPredecessor(VertexInterface<T> predecessor);

   /** Gets the recorded predecessor of this vertex.
       @return  Either this vertex's predecessor or null if no predecessor
                was recorded. */
   public VertexInterface<T> getPredecessor();

   /** Sees whether a predecessor was recorded for this vertex.
       @return  True if a predecessor was recorded. */
   public boolean hasPredecessor();

   /** Records the cost of a path to this vertex.
       @param newCost  The cost of the path. */
   public void setCost(double newCost);

   /** Gets the recorded cost of the path to this vertex.
       @return  The cost of the path. */
   public double getCost();
} // end VertexInterface