// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

/*
Package keystore encrypt private key and save on disk uses JSON encoding.

This key store behaves as KeyStorePlain with the difference that
the private key is encrypted and on disk uses another JSON encoding.

The crypto is documented at https://github.com/ethereum/wiki/wiki/Web3-Secret-Storage-Definition
*/
package keystore

import (
	"bytes"
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io"

	"github.com/deltaswapio/swaprouter/v3/common/math"
	"github.com/deltaswapio/swaprouter/v3/tools/crypto"
	"github.com/pborman/uuid"
	"golang.org/x/crypto/pbkdf2"
	"golang.org/x/crypto/scrypt"
)

const (
	keyHeaderKDF = "scrypt"

	// StandardScryptN is the N parameter of Scrypt encryption algorithm, using 256MB
	// memory and taking approximately 1s CPU time on a modern processor.
	StandardScryptN = 1 << 18

	// StandardScryptP is the P parameter of Scrypt encryption algorithm, using 256MB
	// memory and taking approximately 1s CPU time on a modern processor.
	StandardScryptP = 1

	// LightScryptN is the N parameter of Scrypt encryption algorithm, using 4MB
	// memory and taking approximately 100ms CPU time on a modern processor.
	LightScryptN = 1 << 12

	// LightScryptP is the P parameter of Scrypt encryption algorithm, using 4MB
	// memory and taking approximately 100ms CPU time on a modern processor.
	LightScryptP = 6

	scryptR     = 8
	scryptDKLen = 32
)

// ErrDecrypt decrypt error
var ErrDecrypt = errors.New("could not decrypt key with given password")

// EncryptDataV3 encrypts the data given as 'data' with the password 'auth'.
func EncryptDataV3(data, auth []byte, scryptN, scryptP int) (CryptoJSON, error) {
	salt := make([]byte, 32)
	if _, err := io.ReadFull(rand.Reader, salt); err != nil {
		panic("reading from crypto/rand failed: " + err.Error())
	}
	derivedKey, err := scrypt.Key(auth, salt, scryptN, scryptR, scryptP, scryptDKLen)
	if err != nil {
		return CryptoJSON{}, err
	}
	encryptKey := derivedKey[:16]

	iv := make([]byte, aes.BlockSize) // 16
	if _, err = io.ReadFull(rand.Reader, iv); err != nil {
		panic("reading from crypto/rand failed: " + err.Error())
	}
	cipherText, err := aesCTRXOR(encryptKey, data, iv)
	if err != nil {
		return CryptoJSON{}, err
	}
	mac := crypto.Keccak256(derivedKey[16:32], cipherText)

	scryptParamsJSON := make(map[string]interface{}, 5)
	scryptParamsJSON["n"] = scryptN
	scryptParamsJSON["r"] = scryptR
	scryptParamsJSON["p"] = scryptP
	scryptParamsJSON["dklen"] = scryptDKLen
	scryptParamsJSON["salt"] = hex.EncodeToString(salt)
	cipherParamsJSON := cipherparamsJSON{
		IV: hex.EncodeToString(iv),
	}

	cryptoStruct := CryptoJSON{
		Cipher:       "aes-128-ctr",
		CipherText:   hex.EncodeToString(cipherText),
		CipherParams: cipherParamsJSON,
		KDF:          keyHeaderKDF,
		KDFParams:    scryptParamsJSON,
		MAC:          hex.EncodeToString(mac),
	}
	return cryptoStruct, nil
}

// EncryptKey encrypts a key using the specified scrypt parameters into a json
// blob that can be decrypted later on.
func EncryptKey(key *Key, auth string, scryptN, scryptP int) ([]byte, error) {
	keyBytes := math.PaddedBigBytes(key.PrivateKey.D, 32)
	cryptoStruct, err := EncryptDataV3(keyBytes, []byte(auth), scryptN, scryptP)
	if err != nil {
		return nil, err
	}
	encryptKeyJSONV3 := encryptedKeyJSONV3{
		hex.EncodeToString(key.Address[:]),
		cryptoStruct,
		key.ID.String(),
		version,
	}
	return json.Marshal(encryptKeyJSONV3)
}

// DecryptKey decrypts a key from a json blob, returning the private key itself.
func DecryptKey(keyjson []byte, auth string) (*Key, error) {
	k := new(encryptedKeyJSONV3)
	err := json.Unmarshal(keyjson, k)
	if err != nil {
		return nil, err
	}
	keyBytes, keyID, err := decryptKeyV3(k, auth)
	// Handle any decryption errors and return the key
	if err != nil {
		return nil, err
	}
	key, err := crypto.ToECDSA(keyBytes)
	if err != nil {
		return nil, ErrDecrypt
	}

	return &Key{
		ID:         uuid.UUID(keyID),
		Address:    crypto.PubkeyToAddress(key.PublicKey),
		PrivateKey: key,
	}, nil
}

// DecryptDataV3 decrypt
func DecryptDataV3(cryptoJSON *CryptoJSON, auth string) ([]byte, error) {
	if cryptoJSON.Cipher != "aes-128-ctr" {
		return nil, fmt.Errorf("cipher not supported: %v", cryptoJSON.Cipher)
	}
	mac, err := hex.DecodeString(cryptoJSON.MAC)
	if err != nil {
		return nil, err
	}

	iv, err := hex.DecodeString(cryptoJSON.CipherParams.IV)
	if err != nil {
		return nil, err
	}

	cipherText, err := hex.DecodeString(cryptoJSON.CipherText)
	if err != nil {
		return nil, err
	}

	derivedKey, err := getKDFKey(cryptoJSON, auth)
	if err != nil {
		return nil, err
	}

	calculatedMAC := crypto.Keccak256(derivedKey[16:32], cipherText)
	if !bytes.Equal(calculatedMAC, mac) {
		return nil, ErrDecrypt
	}

	plainText, err := aesCTRXOR(derivedKey[:16], cipherText, iv)
	if err != nil {
		return nil, err
	}
	return plainText, err
}

func decryptKeyV3(keyProtected *encryptedKeyJSONV3, auth string) (keyBytes, keyID []byte, err error) {
	if keyProtected.Version != version {
		return nil, nil, fmt.Errorf("version not supported: %v", keyProtected.Version)
	}
	keyID = uuid.Parse(keyProtected.ID)
	plainText, err := DecryptDataV3(&keyProtected.Crypto, auth)
	if err != nil {
		return nil, nil, err
	}
	return plainText, keyID, err
}

func getKDFKey(cryptoJSON *CryptoJSON, auth string) ([]byte, error) {
	authArray := []byte(auth)
	salt, err := hex.DecodeString(cryptoJSON.KDFParams["salt"].(string))
	if err != nil {
		return nil, err
	}
	dkLen := ensureInt(cryptoJSON.KDFParams["dklen"])

	if cryptoJSON.KDF == keyHeaderKDF {
		n := ensureInt(cryptoJSON.KDFParams["n"])
		r := ensureInt(cryptoJSON.KDFParams["r"])
		p := ensureInt(cryptoJSON.KDFParams["p"])
		return scrypt.Key(authArray, salt, n, r, p, dkLen)
	} else if cryptoJSON.KDF == "pbkdf2" {
		c := ensureInt(cryptoJSON.KDFParams["c"])
		prf := cryptoJSON.KDFParams["prf"].(string)
		if prf != "hmac-sha256" {
			return nil, fmt.Errorf("unsupported PBKDF2 PRF: %s", prf)
		}
		key := pbkdf2.Key(authArray, salt, c, dkLen, sha256.New)
		return key, nil
	}

	return nil, fmt.Errorf("unsupported KDF: %s", cryptoJSON.KDF)
}

// TODO: can we do without this when unmarshalling dynamic JSON?
// why do integers in KDF params end up as float64 and not int after
// unmarshal?
func ensureInt(x interface{}) int {
	res, ok := x.(int)
	if !ok {
		res = int(x.(float64))
	}
	return res
}

func aesCTRXOR(key, inText, iv []byte) ([]byte, error) {
	// AES-128 is selected due to size of encryptKey.
	aesBlock, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	stream := cipher.NewCTR(aesBlock, iv)
	outText := make([]byte, len(inText))
	stream.XORKeyStream(outText, inText)
	return outText, err
}
