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package cryptix.ecc;

import java.math.BigInteger;
import java.security.SecureRandom;
public abstract class GF {

    /**
     * Size of the finite field GF(q)
     */
    protected BigInteger q;

    /**
     * Internal representation of this element
     */
    protected BigInteger v;

    /**
     * Convenient BigInteger constants
     */
    protected static final BigInteger
        ZERO    = BigInteger.valueOf(0L),
        ONE     = BigInteger.valueOf(1L),
        TWO     = BigInteger.valueOf(2L),
        THREE   = BigInteger.valueOf(3L);

    /**
     * Check if this point is equal to a given object
     * 
     * @param   x   the field element to be compared to this
     * 
     * @return  true if this element is equal to x, otherwise false
     */
    public boolean equals(Object x) {
        return x instanceof GF
            && q.equals(((GF)x).q)
            && v.equals(((GF)x).v)
            ;
    }

    /**
     * Create a clone of this element.

     * 

     * This factory method is intended for use with the "Prototype" design
     * pattern as described by E. Gamma, R. Helm, R. Johnson and J. Vlissides
     * in "Design Patterns - Elements of Reusable Object-Oriented Software",
     * Addison-Wesley (1995).

     * 
     * @return  a clone of this finite field element
     */
    public abstract Object clone();

    /**
     * Compute a random element in the same field as this.

     * 

     * This factory method is intended for use with the "Prototype" design
     * pattern as described by E. Gamma, R. Helm, R. Johnson and J. Vlissides
     * in "Design Patterns - Elements of Reusable Object-Oriented Software",
     * Addison-Wesley (1995).
     * 
     * @param   rand    cryptographically strong PRNG
     * 
     * @return  a random element from the same finite field as this
     */
    public abstract GF randomize(SecureRandom rand);

    /**
     * Compute the field element in the same field as this,
     * described by the string val in base radix.

     * 

     * This factory method is intended for use with the "Prototype" design
     * pattern as described by E. Gamma, R. Helm, R. Johnson and J. Vlissides
     * in "Design Patterns - Elements of Reusable Object-Oriented Software",
     * Addison-Wesley (1995).
     * 
     * @param   val     readable description of a finite field element
     * @param   radix   base in which the val description is given
     * 
     * @return  the field element described by val in base radix
     * 
     * @exception   NumberFormatException   if val is not in appropriate format
     */
    public abstract GF translate(String val, int radix) throws NumberFormatException ;

    /**
     * Return the size q of the underlying finite field GF(q)
     * 
     * @return  the size q of the underlying finite field GF(q)
     */
    public BigInteger fieldSize() {
        return q;
    }

    /**
     * Check if this element is the addition neutral element ("zero") of GF(q)
     * 
     * @return  true if this element is zero, otherwise false
     */
    public boolean isZero() {
        return v.signum() == 0;
    }

    /**
     * Check if this element is the multiplication neutral element ("one") of GF(q)
     * 
     * @return  true if this element is one, otherwise false
     */
    public boolean isOne() {
        return v.compareTo(ONE) == 0;
    }