package ShamirSecretSharing;


import org.factcenter.qilin.primitives.CyclicGroup;
import org.factcenter.qilin.primitives.concrete.Zpstar;

import java.math.BigInteger;
import java.util.Random;

/**
 * Created by Tzlil on 1/27/2016.
 */
public class SecretSharing {
    protected final CyclicGroup<BigInteger> group;
    protected final int t;
    protected final int n;
    protected final Polynomial polynomial;

    public SecretSharing(CyclicGroup<BigInteger> group, int t, int n, BigInteger s, Random random) {
        this.group = group;
        this.t = t;
        this.n = n;
        this.polynomial = generateRandomPolynomial(s,random);
    }

    private Polynomial generateRandomPolynomial(BigInteger s, Random random) {
        BigInteger[] coefficients = new BigInteger[t + 1];
        coefficients[0] = s;
        BigInteger p = group.orderUpperBound();
        int bits = p.bitLength();
        for (int i = 1 ; i <= t; i++ ){
            coefficients[i] = new BigInteger(bits,random).mod(p); // sample from Zp [0,... p-1]
        }
        return new Polynomial(coefficients);
    }

    //ToDo make it safe : permission to call this func
    public Polynomial.Point getShare(int i) throws Exception {
        if(i < 1 || i > n){
            throw new Exception();
        }
        return new Polynomial.Point(BigInteger.valueOf(i), polynomial.image(BigInteger.valueOf(i)));
    }

    public static BigInteger getSecrete(Polynomial.Point[] shares){
        Polynomial polynomial = Polynomial.interpolation(shares);
        return polynomial.image(BigInteger.ZERO);
    }

    public int getThreshold() {
        return t;
    }

    public int getN() {
        return n;
    }


}