/* SPDX-License-Identifier: MIT
 *
 * Copyright (C) 2017-2023 WireGuard LLC. All Rights Reserved.
 */

package device

import (
	"crypto/elliptic"
	"crypto/hmac"
	"crypto/rand"
	"crypto/subtle"
	"errors"
	"hash"
	"math/big"

	"github.com/emmansun/gmsm/sm2"
	ecrypto "github.com/ethereum/go-ethereum/crypto"
	"golang.org/x/crypto/blake2s"
)

/* KDF related functions.
 * HMAC-based Key Derivation Function (HKDF)
 * https://tools.ietf.org/html/rfc5869
 */

func HMAC1(sum *[blake2s.Size]byte, key, in0 []byte) {
	mac := hmac.New(func() hash.Hash {
		h, _ := blake2s.New256(nil)
		return h
	}, key)
	mac.Write(in0)
	mac.Sum(sum[:0])
}

func HMAC2(sum *[blake2s.Size]byte, key, in0, in1 []byte) {
	mac := hmac.New(func() hash.Hash {
		h, _ := blake2s.New256(nil)
		return h
	}, key)
	mac.Write(in0)
	mac.Write(in1)
	mac.Sum(sum[:0])
}

func KDF1(t0 *[blake2s.Size]byte, key, input []byte) {
	HMAC1(t0, key, input)
	HMAC1(t0, t0[:], []byte{0x1})
}

func KDF2(t0, t1 *[blake2s.Size]byte, key, input []byte) {
	var prk [blake2s.Size]byte
	HMAC1(&prk, key, input)
	HMAC1(t0, prk[:], []byte{0x1})
	HMAC2(t1, prk[:], t0[:], []byte{0x2})
	setZero(prk[:])
}

func KDF3(t0, t1, t2 *[blake2s.Size]byte, key, input []byte) {
	var prk [blake2s.Size]byte
	HMAC1(&prk, key, input)
	HMAC1(t0, prk[:], []byte{0x1})
	HMAC2(t1, prk[:], t0[:], []byte{0x2})
	HMAC2(t2, prk[:], t1[:], []byte{0x3})
	setZero(prk[:])
}

func isZero(val []byte) bool {
	acc := 1
	for _, b := range val {
		acc &= subtle.ConstantTimeByteEq(b, 0)
	}
	return acc == 1
}

/* This function is not used as pervasively as it should because this is mostly impossible in Go at the moment */
func setZero(arr []byte) {
	for i := range arr {
		arr[i] = 0
	}
}

func (sk *NoisePrivateKey) clamp() {
	//sk[0] &= 248
	//sk[31] = (sk[31] & 127) | 64
}

func newPrivateKey() (sk NoisePrivateKey, err error) {
	if ALGO == SECP256K1 {
		privKey, e := ecrypto.GenerateKey()
		if e == nil {
			sk = NoisePrivateKey(ecrypto.FromECDSA(privKey))
		} else {
			err = e
		}
		return sk, err
	} else if ALGO == SM2 {
		for {
			privKey, e := sm2.GenerateKey(rand.Reader)
			if e == nil {
				b := privKey.D.Bytes()
				if len(b) != NoisePrivateKeySize {
					continue
				}
				sk = NoisePrivateKey(b)
			} else {
				err = e
			}
			return sk, err
		}
	}
	// _, err = rand.Read(sk[:])
	// sk.clamp()
	return sk, errors.New("no such algorithm")
}

func (sk *NoisePrivateKey) publicKey() (pk NoisePublicKey) {
	if ALGO == SECP256K1 {
		privKey, _ := ecrypto.ToECDSA((*sk)[:])
		pubKey := privKey.PublicKey
		pk = NoisePublicKey(ecrypto.CompressPubkey(&pubKey))
	} else if ALGO == SM2 {
		d := new(big.Int).SetBytes((*sk)[:])
		privKey := new(sm2.PrivateKey)
		privKey.Curve = sm2.P256()
		privKey.D = d
		privKey.PublicKey.X, privKey.PublicKey.Y = privKey.ScalarBaseMult(privKey.D.Bytes())
		pk = NoisePublicKey(elliptic.MarshalCompressed(privKey.Curve, privKey.PublicKey.X, privKey.PublicKey.Y))
	}

	// apk := (*[NoisePublicKeySize]byte)(&pk)
	// ask := (*[NoisePrivateKeySize]byte)(sk)
	// curve25519.ScalarBaseMult(apk, ask)
	return pk
}

var errInvalidPublicKey = errors.New("invalid public key")

func (sk *NoisePrivateKey) sharedSecret(pk NoisePublicKey) (ss [NoisePresharedKeySize]byte, err error) {
	var secKeyX *big.Int
	if ALGO == SECP256K1 {
		privKey, e := ecrypto.ToECDSA((*sk)[:])
		if e != nil {
			return ss, e
		}
		pubKey, e := ecrypto.DecompressPubkey(pk[:])
		if e != nil {
			return ss, e
		}
		secKeyX, _ = ecrypto.S256().ScalarMult(pubKey.X, pubKey.Y, privKey.D.Bytes())
	} else if ALGO == SM2 {
		d := new(big.Int).SetBytes((*sk)[:])
		privKey := new(sm2.PrivateKey)
		privKey.Curve = sm2.P256()
		privKey.D = d
		x, y := elliptic.UnmarshalCompressed(privKey.Curve, pk[:])
		secKeyX, _ = privKey.Curve.ScalarMult(x, y, privKey.D.Bytes())
	}
	if secKeyX == nil {
		return ss, errors.New("no such algorithm")
	}
	presharedKey := secKeyX.Bytes()
	keysize := len(presharedKey)
	if keysize < 32 {
		arr := make([]byte, 32-keysize, 32)
		for i := 0; i < 32-keysize; i++ {
			arr[i] = 0
		}
		arr = append(arr, presharedKey...)
		presharedKey = arr
	}
	return ([NoisePresharedKeySize]byte)(presharedKey), nil

	// apk := (*[NoisePublicKeySize]byte)(&pk)
	// ask := (*[NoisePrivateKeySize]byte)(sk)
	// curve25519.ScalarMult(&ss, ask, apk)
	// if isZero(ss[:]) {
	// 	return ss, errInvalidPublicKey
	// }
	// return ss, nil
}