package org.spongycastle.math.ec.custom.sec;

import java.math.BigInteger;

import org.spongycastle.math.ec.ECFieldElement;
import org.spongycastle.math.raw.Mod;
import org.spongycastle.math.raw.Nat192;
import org.spongycastle.util.Arrays;

public class SecP192K1FieldElement extends ECFieldElement
{
    public static final BigInteger Q = SecP192K1Curve.q;

    protected int[] x;

    public SecP192K1FieldElement(BigInteger x)
    {
        if (x == null || x.signum() < 0 || x.compareTo(Q) >= 0)
        {
            throw new IllegalArgumentException("x value invalid for SecP192K1FieldElement");
        }

        this.x = SecP192K1Field.fromBigInteger(x);
    }

    public SecP192K1FieldElement()
    {
        this.x = Nat192.create();
    }

    protected SecP192K1FieldElement(int[] x)
    {
        this.x = x;
    }

    public boolean isZero()
    {
        return Nat192.isZero(x);
    }

    public boolean isOne()
    {
        return Nat192.isOne(x);
    }

    public boolean testBitZero()
    {
        return Nat192.getBit(x, 0) == 1;
    }

    public BigInteger toBigInteger()
    {
        return Nat192.toBigInteger(x);
    }

    public String getFieldName()
    {
        return "SecP192K1Field";
    }

    public int getFieldSize()
    {
        return Q.bitLength();
    }

    public ECFieldElement add(ECFieldElement b)
    {
        int[] z = Nat192.create();
        SecP192K1Field.add(x, ((SecP192K1FieldElement)b).x, z);
        return new SecP192K1FieldElement(z);
    }

    public ECFieldElement addOne()
    {
        int[] z = Nat192.create();
        SecP192K1Field.addOne(x, z);
        return new SecP192K1FieldElement(z);
    }

    public ECFieldElement subtract(ECFieldElement b)
    {
        int[] z = Nat192.create();
        SecP192K1Field.subtract(x, ((SecP192K1FieldElement)b).x, z);
        return new SecP192K1FieldElement(z);
    }

    public ECFieldElement multiply(ECFieldElement b)
    {
        int[] z = Nat192.create();
        SecP192K1Field.multiply(x, ((SecP192K1FieldElement)b).x, z);
        return new SecP192K1FieldElement(z);
    }

    public ECFieldElement divide(ECFieldElement b)
    {
//        return multiply(b.invert());
        int[] z = Nat192.create();
        Mod.invert(SecP192K1Field.P, ((SecP192K1FieldElement)b).x, z);
        SecP192K1Field.multiply(z, x, z);
        return new SecP192K1FieldElement(z);
    }

    public ECFieldElement negate()
    {
        int[] z = Nat192.create();
        SecP192K1Field.negate(x, z);
        return new SecP192K1FieldElement(z);
    }

    public ECFieldElement square()
    {
        int[] z = Nat192.create();
        SecP192K1Field.square(x, z);
        return new SecP192K1FieldElement(z);
    }

    public ECFieldElement invert()
    {
//        return new SecP192K1FieldElement(toBigInteger().modInverse(Q));
        int[] z = Nat192.create();
        Mod.invert(SecP192K1Field.P, x, z);
        return new SecP192K1FieldElement(z);
    }

    /**
     * return a sqrt root - the routine verifies that the calculation returns the right value - if
     * none exists it returns null.
     */
    public ECFieldElement sqrt()
    {
        /*
         * Raise this element to the exponent 2^190 - 2^30 - 2^10 - 2^6 - 2^5 - 2^4 - 2^1
         * 
         * Breaking up the exponent's binary representation into "repunits", we get:
         * { 159 1s } { 1 0s } { 19 1s } { 1 0s } { 3 1s } { 3 0s} { 3 1s } { 1 0s }
         * 
         * Therefore we need an addition chain containing 3, 19, 159 (the lengths of the repunits)
         * We use: 1, 2, [3], 6, 8, 16, [19], 35, 70, 140, [159]
         */

        int[] x1 = this.x;
        if (Nat192.isZero(x1) || Nat192.isOne(x1))
        {
            return this;
        }

        int[] x2 = Nat192.create();
        SecP192K1Field.square(x1, x2);
        SecP192K1Field.multiply(x2, x1, x2);
        int[] x3 = Nat192.create();
        SecP192K1Field.square(x2, x3);
        SecP192K1Field.multiply(x3, x1, x3);
        int[] x6 = Nat192.create();
        SecP192K1Field.squareN(x3, 3, x6);
        SecP192K1Field.multiply(x6, x3, x6);
        int[] x8 = x6;
        SecP192K1Field.squareN(x6, 2, x8);
        SecP192K1Field.multiply(x8, x2, x8);
        int[] x16 = x2;
        SecP192K1Field.squareN(x8, 8, x16);
        SecP192K1Field.multiply(x16, x8, x16);
        int[] x19 = x8;
        SecP192K1Field.squareN(x16, 3, x19);
        SecP192K1Field.multiply(x19, x3, x19);
        int[] x35 = Nat192.create();
        SecP192K1Field.squareN(x19, 16, x35);
        SecP192K1Field.multiply(x35, x16, x35);
        int[] x70 = x16;
        SecP192K1Field.squareN(x35, 35, x70);
        SecP192K1Field.multiply(x70, x35, x70);
        int[] x140 = x35;
        SecP192K1Field.squareN(x70, 70, x140);
        SecP192K1Field.multiply(x140, x70, x140);
        int[] x159 = x70;
        SecP192K1Field.squareN(x140, 19, x159);
        SecP192K1Field.multiply(x159, x19, x159);

        int[] t1 = x159;
        SecP192K1Field.squareN(t1, 20, t1);
        SecP192K1Field.multiply(t1, x19, t1);
        SecP192K1Field.squareN(t1, 4, t1);
        SecP192K1Field.multiply(t1, x3, t1);
        SecP192K1Field.squareN(t1, 6, t1);
        SecP192K1Field.multiply(t1, x3, t1);
        SecP192K1Field.square(t1, t1);

        int[] t2 = x3;
        SecP192K1Field.square(t1, t2);

        return Nat192.eq(x1, t2) ? new SecP192K1FieldElement(t1) : null;        
    }

    public boolean equals(Object other)
    {
        if (other == this)
        {
            return true;
        }

        if (!(other instanceof SecP192K1FieldElement))
        {
            return false;
        }

        SecP192K1FieldElement o = (SecP192K1FieldElement)other;
        return Nat192.eq(x, o.x);
    }

    public int hashCode()
    {
        return Q.hashCode() ^ Arrays.hashCode(x, 0, 6);
    }
}
