package edu.stanford.peer.rbtm.credential;

import java.util.*;

public class Intersection implements EntityExpression
{
    /**
     * The parts of the intersection
     */
    protected LinkedList parts;

    /** 
     * Default constructor. Expressions to be intersected may be added using
     * the and() method.
     */
    public Intersection() {  parts = new LinkedList(); }

    /**
     * Default copy constructor. All part references are duplicated, so the
     * new copy is not relying on the old ones parts list.
     */
    public Intersection(Intersection i) {
	this();
	Iterator it = i.getParts();
	while(it.hasNext())
	    parts.add(it.next());
    }
    
    /**
     * Adds a new expression to this intersection. And() calls may be 
     * concatenated similar to appending with a StringBuffer instance.
     * @param expr An expression to be added (a role or linked role)
     * @return The updated intersection expression
     */
    public Intersection and(EntityExpression expr) {
	parts.add(expr);
	return this;
    }

    /**
     * Public accessor method for accessing each expression in the 
     * intersection. 
     */
    public Iterator getParts() { return parts.iterator(); }

    /**
     * Public access method for determining the number of subexpressions
     * contained in this intersection.
     */
    public int getPartsCount() { return parts.size(); }

    /**
     * Compare the parts of two intersections.
     * @return a boolean result for equivalence
     */
    public boolean equals(Object o) {
	return (o instanceof Intersection)
	    &&  parts.equals(((Intersection)o).parts);
    }

    /**
     * 
     * @return a unique hashcode base on the parts of the intersection.
     */
    public int hashCode() { return parts.hashCode(); }

    /**
     * Converts the intersection into a human readable form. Expressions
     * are separated using a '^' symbol to represent an intersection.
     *
     * @return formatted string representation of an intersection
     */
    public String toString() {
	Iterator i = getParts();
	StringBuffer buff = new StringBuffer();

	while(i.hasNext()) {
	    buff.append(i.next().toString());
	    if(i.hasNext())buff.append(" ^ ");
	}
	return buff.toString();
    }
      
	    

}