/*
 * @(#)ECPoint.java	1.4 05/11/17
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */
package java.security.spec;

import java.math.BigInteger;

/**
 * This immutable class represents a point on an elliptic curve (EC)
 * in affine coordinates. Other coordinate systems can
 * extend this class to represent this point in other
 * coordinates.
 *
 * @author Valerie Peng
 * @version 1.4, 11/17/05
 *
 * @since 1.5
 */
public class ECPoint {

    private final BigInteger x;
    private final BigInteger y;

    /**
     * This defines the point at infinity.
     */
    public static final ECPoint POINT_INFINITY = new ECPoint();

    // private constructor for constructing point at infinity
    private ECPoint() {
	this.x = null;
	this.y = null;
    }

    /**
     * Creates an ECPoint from the specified affine x-coordinate
     * <code>x</code> and affine y-coordinate <code>y</code>.
     * @param x the affine x-coordinate.
     * @param y the affine y-coordinate.
     * @exception NullPointerException if <code>x</code> or 
     * <code>y</code> is null.
     */
    public ECPoint(BigInteger x, BigInteger y) {
	if ((x==null) || (y==null)) {
	    throw new NullPointerException("affine coordinate x or y is null");
	}
	this.x = x;
	this.y = y;
    }

    /**
     * Returns the affine x-coordinate <code>x</code>.
     * Note: POINT_INFINITY has a null affine x-coordinate.
     * @return the affine x-coordinate.
     */
    public BigInteger getAffineX() {
	return x;
    }

    /**
     * Returns the affine y-coordinate <code>y</code>.
     * Note: POINT_INFINITY has a null affine y-coordinate.
     * @return the affine y-coordinate.
     */
    public BigInteger getAffineY() {
	return y;
    }

    /**
     * Compares this elliptic curve point for equality with
     * the specified object. 
     * @param obj the object to be compared.
     * @return true if <code>obj</code> is an instance of 
     * ECPoint and the affine coordinates match, false otherwise.
     */
    public boolean equals(Object obj) {
	if (this == obj) return true;
	if (this == POINT_INFINITY) return false;
	if (obj instanceof ECPoint) {
	    return ((x.equals(((ECPoint)obj).x)) && 
		    (y.equals(((ECPoint)obj).y)));
	}
	return false;
    }

    /**
     * Returns a hash code value for this elliptic curve point.
     * @return a hash code value.
     */
    public int hashCode() {
	if (this == POINT_INFINITY) return 0;
	return x.hashCode() << 5 + y.hashCode();
    }
}
