package sdk

import (
	"PaymentCenter/app/third/paymentService/psbc/internal/gmutil/sm2/util"
	"crypto/elliptic"
	"encoding/binary"
	"math/big"
)

// ZbSdk 众邦
type ZbSdk struct {
	BaseSdk
}

func NewZbSdk() SDK {
	return &ZbSdk{}
}

func (zb *ZbSdk) Kdf(c elliptic.Curve, x, y *big.Int, c2 []byte) error {
	data := elliptic.Marshal(c, x, y)
	ct := uint32(1)
	length := len(c2)
	end := (length + 31) / 32
	result := make([]byte, 0)
	for i := 1; i <= end; i++ {
		bytes, err := zb.sm3hash(data, zb.uint32ToBytes(ct))
		if err != nil {
			return err
		}
		result = append(result, bytes...)
		ct++
	}
	last, err := zb.sm3hash(data, zb.uint32ToBytes(ct))
	if err != nil {
		return err
	}
	if length%32 == 0 {
		result = append(result, last...)
	} else {
		result = append(result, last[:length%32]...)
	}
	for i := 0; i < length; i++ {
		c2[i] ^= result[i]
	}
	return nil
}

func (zb *ZbSdk) CalculateHash(x *big.Int, c2 []byte, y *big.Int) []byte {
	digest := util.New()
	digest.Write(zb.bigIntToByte(x))
	digest.Write(c2)
	digest.Write(zb.bigIntToByte(y))
	result := digest.Sum(nil)[:32]
	return result
}

func (zb *ZbSdk) GetZ(x *big.Int, y *big.Int, uid []byte) []byte {
	z := util.New()
	uidLen := len(uid) * 8
	z.Write([]byte{byte((uidLen >> 8) & 0xFF)})
	z.Write([]byte{byte(uidLen & 0xFF)})
	z.Write(uid)

	sm2P256 := util.NewP256Sm2()

	z.Write(zb.bigIntToByte(sm2P256.A))
	z.Write(zb.bigIntToByte(sm2P256.B))
	z.Write(zb.bigIntToByte(sm2P256.Gx))
	z.Write(zb.bigIntToByte(sm2P256.Gy))

	z.Write(x.Bytes())
	z.Write(y.Bytes())
	return z.Sum(nil)
}

func (zb *ZbSdk) bigIntToByte(n *big.Int) []byte {
	byteArray := n.Bytes()

	// If the most significant byte's most significant bit is set,
	// prepend a 0 byte to the slice to avoid being interpreted as a negative number.
	if (byteArray[0] & 0x80) != 0 {
		byteArray = append([]byte{0}, byteArray...)
	}
	return byteArray
}

func (zb *ZbSdk) uint32ToBytes(x uint32) []byte {
	var buf = make([]byte, 4)
	binary.LittleEndian.PutUint32(buf, x)
	return buf
}