/**
   This class implements half-edges which are either 
   unary, i.e. a state or binary, i.e. a
   pair formed by a  word and a state or 
   ternary, i.e. triples of
   two words (input and output) and a state.
*/
public class HalfEdge implements Comparable{
    String label1;
    String label2;
    int end;
    /**
       Creates a unary half-edge.
    */
    public HalfEdge(int q){
	end = q;
    }
    /**
       Creates a binary half-edge.
    */
    public HalfEdge(String s,int q){
	label1 = s;
	end = q;
    }
    /**
       Creates a ternary half-egde.
    */
    public HalfEdge(String s, String t, int q){
	label1 =s;
	label2 = t;
	end=q;
    }
    /**
       Overrides the method <code>Object.compareTo</code>. Orders the half-edges
       lexicographically first by end, then by input label and last
       by output label.
    */
    public int compareTo(Object o){
	HalfEdge f = (HalfEdge) o;
	if(end < f.end)
	    return -1;
	if(end > f.end)
	    return 1;
	if(label1 == null)
	    return 0;
	int v = label1.compareTo(f.label1);
	if(v != 0 || label2 == null)
	    return v;
	return label2.compareTo(f.label2);
    }
    /**
       Overrides the method <code>Object.hashCode</code>.
    */
    public boolean equals(Object o){
	return compareTo(o) == 0;
    }
    /**
       Overrides the method <code>Object.hashCode</code>. The hashcode of a half-edge
       is <ul>
       <li> <code>end</code> if there are no labels.
       <li> <code>hashcode(label1) + end</code> if there is one label.
       <li> <code>hashcode(label1) + hashcode(label2) + end</code> 
       if there are two labels.
       </ul>
    */
    public int hashCode(){
	return (label1 == null) ? 
	    end: 
	    ((label2 == null) ? 
	     end + label1.hashCode() : 
	     end + label1.hashCode() +  label2.hashCode());
    }
    /**
       Overrides the method <code>toString</code>
    */
    public String toString(){
	if(label1 == null)
	    return "(" + end + ")";
	if(label2 == null)
	    return "(" + label1 +"," + end + ")";
	return "(" + label1 + "," + label2 + "," + end + ")";
    }


}