// Copyright 2014 The go-ethereum Authors
// (original work)
// Copyright 2024 The Erigon Authors
// (modifications)
// This file is part of Erigon.
//
// Erigon 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.
//
// Erigon 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 Erigon. If not, see <http://www.gnu.org/licenses/>.

package crypto

import (
	"bufio"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"math/big"
	"os"
	"sync"

	keccak "github.com/erigontech/fastkeccak"
	"github.com/holiman/uint256"
	"golang.org/x/crypto/sha3"

	"github.com/erigontech/erigon/common"
	"github.com/erigontech/erigon/common/hexutil"
	"github.com/erigontech/erigon/common/math"
)

// SignatureLength indicates the byte length required to carry a signature with recovery id.
const SignatureLength = 64 + 1 // 64 bytes ECDSA signature + 1 byte recovery id

// RecoveryIDOffset points to the byte offset within the signature that contains the recovery id.
const RecoveryIDOffset = 64

// DigestLength sets the signature digest exact length
const DigestLength = 32

var (
	secp256k1N     = *new(uint256.Int).SetBytes(hexutil.MustDecode("0xfffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141"))
	secp256k1NBig  = secp256k1N.ToBig()
	secp256k1halfN = new(uint256.Int).Rsh(&secp256k1N, 1)
)

var errInvalidPubkey = errors.New("invalid secp256k1 public key")

// EllipticCurve contains curve operations.
type EllipticCurve interface {
	elliptic.Curve

	// Point marshaling/unmarshaing.
	Marshal(x, y *big.Int) []byte
	Unmarshal(data []byte) (x, y *big.Int)
}

// HashData hashes the provided data and returns a 32 byte hash.
func HashData(data []byte) common.Hash {
	return keccak.Sum256(data)
}

// Keccak256 calculates and returns the Keccak256 hash of the input data.
func Keccak256(data ...[]byte) []byte {
	b := make([]byte, 32)
	d := NewKeccakState()
	for _, b := range data {
		d.Write(b)
	}
	d.Read(b) //nolint:errcheck
	ReturnToPool(d)
	return b
}

// Keccak256Hash calculates and returns the Keccak256 hash of the input data,
// converting it to an internal Hash data structure.
func Keccak256Hash(data ...[]byte) common.Hash {
	d := NewKeccakState()
	for _, b := range data {
		d.Write(b)
	}
	h := FinalizeHash(d)
	ReturnToPool(d)
	return h
}

// Keccak512 calculates and returns the Keccak512 hash of the input data.
func Keccak512(data ...[]byte) []byte {
	d := sha3.NewLegacyKeccak512()
	for _, b := range data {
		d.Write(b)
	}
	return d.Sum(nil)
}

// ToECDSA creates a private key with the given D value.
func ToECDSA(d []byte) (*ecdsa.PrivateKey, error) {
	return toECDSA(d, true)
}

// toECDSA creates a private key with the given D value. The strict parameter
// controls whether the key's length should be enforced at the curve size or
// it can also accept legacy encodings (0 prefixes).
func toECDSA(d []byte, strict bool) (*ecdsa.PrivateKey, error) {
	priv := new(ecdsa.PrivateKey)
	priv.PublicKey.Curve = S256()
	if strict && 8*len(d) != priv.Params().BitSize {
		return nil, fmt.Errorf("invalid length, need %d bits", priv.Params().BitSize)
	}
	priv.D = new(big.Int).SetBytes(d)

	// The priv.D must < N
	if priv.D.Cmp(secp256k1NBig) >= 0 {
		return nil, errors.New("invalid private key, >=N")
	}
	// The priv.D must not be zero or negative.
	if priv.D.Sign() <= 0 {
		return nil, errors.New("invalid private key, zero or negative")
	}

	priv.PublicKey.X, priv.PublicKey.Y = S256().ScalarBaseMult(d)
	if priv.PublicKey.X == nil {
		return nil, errors.New("invalid private key")
	}
	return priv, nil
}

// FromECDSA exports a private key into a binary dump.
func FromECDSA(priv *ecdsa.PrivateKey) []byte {
	if priv == nil {
		return nil
	}
	return math.PaddedBigBytes(priv.D, priv.Params().BitSize/8)
}

// UnmarshalPubkeyStd parses a public key from the given bytes in the standard "uncompressed" format.
// The input slice must be 65 bytes long and have this format: [4, X..., Y...]
// See MarshalPubkeyStd.
func UnmarshalPubkeyStd(pub []byte) (*ecdsa.PublicKey, error) {
	x, y := S256().Unmarshal(pub)
	if x == nil {
		return nil, errInvalidPubkey
	}
	if !S256().IsOnCurve(x, y) {
		return nil, errInvalidPubkey
	}
	return &ecdsa.PublicKey{Curve: S256(), X: x, Y: y}, nil
}

// MarshalPubkeyStd converts a public key into the standard "uncompressed" format.
// It returns a 65 bytes long slice that contains: [4, X..., Y...]
// Returns nil if the given public key is not initialized.
// See UnmarshalPubkeyStd.
func MarshalPubkeyStd(pub *ecdsa.PublicKey) []byte {
	if pub == nil || pub.X == nil || pub.Y == nil {
		return nil
	}
	return S256().Marshal(pub.X, pub.Y)
}

// UnmarshalPubkey parses a public key from the given bytes in the 64 bytes "uncompressed" format.
// The input slice must be 64 bytes long and have this format: [X..., Y...]
// See MarshalPubkey.
func UnmarshalPubkey(keyBytes []byte) (*ecdsa.PublicKey, error) {
	buf := make([]byte, 1+len(keyBytes))
	buf[0] = 0x4
	copy(buf[1:], keyBytes)
	return UnmarshalPubkeyStd(buf)
}

// MarshalPubkey converts a public key into a 64 bytes "uncompressed" format.
// It returns a 64 bytes long slice that contains: [X..., Y...]
// In the standard 65 bytes format the first byte is always constant (equal to 4),
// so it can be cut off and trivially recovered later.
// Returns nil if the given public key is not initialized.
// See UnmarshalPubkey.
func MarshalPubkey(pubkey *ecdsa.PublicKey) []byte {
	keyBytes := MarshalPubkeyStd(pubkey)
	if keyBytes == nil {
		return nil
	}
	return keyBytes[1:]
}

// FromECDSAPub converts a secp256k1 public key to bytes.
// Note: it does not use the curve from pub, instead it always
// encodes using secp256k1.
func FromECDSAPub(pub *ecdsa.PublicKey) []byte {
	if pub == nil || pub.X == nil || pub.Y == nil {
		return nil
	}
	return S256().Marshal(pub.X, pub.Y)
}

// HexToECDSA parses a secp256k1 private key.
func HexToECDSA(hexkey string) (*ecdsa.PrivateKey, error) {
	b, err := hex.DecodeString(hexkey)
	var byteErr hex.InvalidByteError
	if errors.As(err, &byteErr) {
		return nil, fmt.Errorf("invalid hex character %q in private key", byte(byteErr))
	} else if err != nil {
		return nil, errors.New("invalid hex data for private key")
	}
	return ToECDSA(b)
}

// LoadECDSA loads a secp256k1 private key from the given file.
func LoadECDSA(file string) (*ecdsa.PrivateKey, error) {
	fd, err := os.Open(file)
	if err != nil {
		return nil, err
	}
	defer fd.Close()

	r := bufio.NewReader(fd)
	buf := make([]byte, 64)
	n, err := readASCII(buf, r)
	if err != nil {
		return nil, err
	} else if n != len(buf) {
		return nil, errors.New("key file too short, want 64 hex characters")
	}
	if err := checkKeyFileEnd(r); err != nil {
		return nil, err
	}

	return HexToECDSA(string(buf))
}

// readASCII reads into 'buf', stopping when the buffer is full or
// when a non-printable control character is encountered.
func readASCII(buf []byte, r *bufio.Reader) (n int, err error) {
	for ; n < len(buf); n++ {
		buf[n], err = r.ReadByte()
		switch {
		case errors.Is(err, io.EOF) || buf[n] < '!':
			return n, nil
		case err != nil:
			return n, err
		}
	}
	return n, nil
}

// checkKeyFileEnd skips over additional newlines at the end of a key file.
func checkKeyFileEnd(r *bufio.Reader) error {
	for i := 0; ; i++ {
		b, err := r.ReadByte()
		switch {
		case errors.Is(err, io.EOF):
			return nil
		case err != nil:
			return err
		case b != '\n' && b != '\r':
			return fmt.Errorf("invalid character %q at end of key file", b)
		case i >= 2:
			return errors.New("key file too long, want 64 hex characters")
		}
	}
}

// SaveECDSA saves a secp256k1 private key to the given file with
// restrictive permissions. The key data is saved hex-encoded.
func SaveECDSA(file string, key *ecdsa.PrivateKey) error {
	k := hex.EncodeToString(FromECDSA(key))
	return os.WriteFile(file, []byte(k), 0600)
}

// GenerateKey generates a new private key.
func GenerateKey() (*ecdsa.PrivateKey, error) {
	return ecdsa.GenerateKey(S256(), rand.Reader)
}

// See Appendix F "Signing Transactions" of the Yellow Paper
func TransactionSignatureIsValid(v byte, r, s *uint256.Int, allowPreEip2s bool) bool {
	if r.IsZero() || s.IsZero() {
		return false
	}

	// See EIP-2: Homestead Hard-fork Changes
	if !allowPreEip2s && s.Gt(secp256k1halfN) {
		return false
	}

	return r.Lt(&secp256k1N) && s.Lt(&secp256k1N) && (v == 0 || v == 1)
}

// DESCRIBED: docs/programmers_guide/guide.md#address---identifier-of-an-account
func PubkeyToAddress(p ecdsa.PublicKey) common.Address {
	pubBytes := MarshalPubkey(&p)
	return common.BytesToAddress(Keccak256(pubBytes)[12:])
}

// hasherPool holds LegacyKeccak hashers.
var hasherPool = sync.Pool{
	New: func() any {
		return keccak.NewFastKeccak()
	},
}

// NewKeccakState creates a new KeccakState
func NewKeccakState() keccak.KeccakState {
	h := hasherPool.Get().(keccak.KeccakState)
	h.Reset()
	return h
}
func ReturnToPool(h keccak.KeccakState) { hasherPool.Put(h) }

// FinalizeHash finalizes sha and returns a Keccak-256 digest as a value type,
// avoiding the heap escape that occurs when passing h[:] to an interface Read method.
func FinalizeHash(sha keccak.KeccakState) common.Hash {
	if h, ok := sha.(*keccak.Hasher); ok {
		return h.Sum256()
	}
	var out common.Hash
	sha.Read(out[:]) //nolint:errcheck
	return out
}
