package kzgceremony

import (
	"math/big"

	"github.com/ethereum/go-ethereum/crypto/bls12381"
)

type Contribution struct {
	SRS *SRS
}

type SRS struct {
	G1s []*bls12381.PointG1
	G2s []*bls12381.PointG2
}

type toxicWaste struct {
	tau   *big.Int
	TauG2 *bls12381.PointG2
}

// newEmptySRS creates an empty SRS
func newEmptySRS(nG1, nG2 int) *SRS {
	g1s := make([]*bls12381.PointG1, nG1)
	g2s := make([]*bls12381.PointG2, nG2)
	g1 := bls12381.NewG1()
	g2 := bls12381.NewG2()
	// one_G1 := g1.One()
	// one_G2 := g2.One()
	for i := 0; i < nG1; i++ {
		g1s[i] = g1.One()
		// g1.MulScalar(g1s[i], one_G1, big.NewInt(int64(i)))
	}
	for i := 0; i < nG2; i++ {
		g2s[i] = g2.One()
		// g2.MulScalar(g2s[i], one_G2, big.NewInt(int64(i)))
	}
	return &SRS{g1s, g2s}
}

func tau(randomness []byte) *toxicWaste {
	g2 := bls12381.NewG2()
	tau := new(big.Int).Mod(
		new(big.Int).SetBytes(randomness),
		g2.Q())
	TauG2 := g2.New()
	g2.MulScalar(TauG2, g2.One(), tau)

	return &toxicWaste{tau, TauG2}
}

func computeContribution(t *toxicWaste, prevSRS *SRS) *SRS {
	srs := newEmptySRS(len(prevSRS.G1s), len(prevSRS.G2s))
	g1 := bls12381.NewG1()
	g2 := bls12381.NewG2()
	Q := g1.Q() // Q = |G1| == |G2|

	for i := 0; i < len(prevSRS.G1s); i++ {
		tau_i := new(big.Int).Exp(t.tau, big.NewInt(int64(i)), Q)
		g1.MulScalar(srs.G1s[i], prevSRS.G1s[i], tau_i)
	}
	for i := 0; i < len(prevSRS.G2s); i++ {
		tau_i := new(big.Int).Exp(t.tau, big.NewInt(int64(i)), Q)
		g2.MulScalar(srs.G2s[i], prevSRS.G2s[i], tau_i)
	}

	return srs
}

// Contribute
func Contribute(prevSRS *SRS, randomness []byte) (Contribution, error) {
	// set tau from randomness
	tw := tau(randomness)

	newSRS := computeContribution(tw, prevSRS)

	return Contribution{SRS: newSRS}, nil
}