// 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 vm

import (
	"crypto/sha256"
	"errors"
	"math/big"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/math"
	"github.com/ethereum/go-ethereum/crypto"
	"github.com/ethereum/go-ethereum/crypto/bn256"
	"github.com/ethereum/go-ethereum/params"
	"golang.org/x/crypto/ripemd160"
)

// PrecompiledContract is the basic interface for native Go contracts. The implementation
// requires a deterministic gas count based on the input size of the Run method of the
// contract.
type PrecompiledContract interface {
	RequiredGas(input []byte) uint64  // RequiredPrice calculates the contract gas use
	Run(input []byte) ([]byte, error) // Run runs the precompiled contract
}

// PrecompiledContractsHomestead contains the default set of pre-compiled Ethereum
// contracts used in the Frontier and Homestead releases.
var PrecompiledContractsHomestead = map[common.Address]PrecompiledContract{
	common.BytesToAddress([]byte{1}): &ecrecover{},
	common.BytesToAddress([]byte{2}): &sha256hash{},
	common.BytesToAddress([]byte{3}): &ripemd160hash{},
	common.BytesToAddress([]byte{4}): &dataCopy{},
}

// PrecompiledContractsMetropolis contains the default set of pre-compiled Ethereum
// contracts used in the Metropolis release.
var PrecompiledContractsMetropolis = map[common.Address]PrecompiledContract{
	common.BytesToAddress([]byte{1}): &ecrecover{},
	common.BytesToAddress([]byte{2}): &sha256hash{},
	common.BytesToAddress([]byte{3}): &ripemd160hash{},
	common.BytesToAddress([]byte{4}): &dataCopy{},
	common.BytesToAddress([]byte{5}): &bigModExp{},
	common.BytesToAddress([]byte{6}): &bn256Add{},
	common.BytesToAddress([]byte{7}): &bn256ScalarMul{},
	common.BytesToAddress([]byte{8}): &bn256Pairing{},
}

// RunPrecompiledContract runs and evaluates the output of a precompiled contract.
func RunPrecompiledContract(p PrecompiledContract, input []byte, contract *Contract) (ret []byte, err error) {
	gas := p.RequiredGas(input)
	if contract.UseGas(gas) {
		return p.Run(input)
	}
	return nil, ErrOutOfGas
}

// ECRECOVER implemented as a native contract.
type ecrecover struct{}

func (c *ecrecover) RequiredGas(input []byte) uint64 {
	return params.EcrecoverGas
}

func (c *ecrecover) Run(input []byte) ([]byte, error) {
	const ecRecoverInputLength = 128

	input = common.RightPadBytes(input, ecRecoverInputLength)
	// "input" is (hash, v, r, s), each 32 bytes
	// but for ecrecover we want (r, s, v)

	r := new(big.Int).SetBytes(input[64:96])
	s := new(big.Int).SetBytes(input[96:128])
	v := input[63] - 27

	// tighter sig s values input homestead only apply to tx sigs
	if !allZero(input[32:63]) || !crypto.ValidateSignatureValues(v, r, s, false) {
		return nil, nil
	}
	// v needs to be at the end for libsecp256k1
	pubKey, err := crypto.Ecrecover(input[:32], append(input[64:128], v))
	// make sure the public key is a valid one
	if err != nil {
		return nil, nil
	}

	// the first byte of pubkey is bitcoin heritage
	return common.LeftPadBytes(crypto.Keccak256(pubKey[1:])[12:], 32), nil
}

// SHA256 implemented as a native contract.
type sha256hash struct{}

// RequiredGas returns the gas required to execute the pre-compiled contract.
//
// This method does not require any overflow checking as the input size gas costs
// required for anything significant is so high it's impossible to pay for.
func (c *sha256hash) RequiredGas(input []byte) uint64 {
	return uint64(len(input)+31)/32*params.Sha256PerWordGas + params.Sha256BaseGas
}
func (c *sha256hash) Run(input []byte) ([]byte, error) {
	h := sha256.Sum256(input)
	return h[:], nil
}

// RIPMED160 implemented as a native contract.
type ripemd160hash struct{}

// RequiredGas returns the gas required to execute the pre-compiled contract.
//
// This method does not require any overflow checking as the input size gas costs
// required for anything significant is so high it's impossible to pay for.
func (c *ripemd160hash) RequiredGas(input []byte) uint64 {
	return uint64(len(input)+31)/32*params.Ripemd160PerWordGas + params.Ripemd160BaseGas
}
func (c *ripemd160hash) Run(input []byte) ([]byte, error) {
	ripemd := ripemd160.New()
	ripemd.Write(input)
	return common.LeftPadBytes(ripemd.Sum(nil), 32), nil
}

// data copy implemented as a native contract.
type dataCopy struct{}

// RequiredGas returns the gas required to execute the pre-compiled contract.
//
// This method does not require any overflow checking as the input size gas costs
// required for anything significant is so high it's impossible to pay for.
func (c *dataCopy) RequiredGas(input []byte) uint64 {
	return uint64(len(input)+31)/32*params.IdentityPerWordGas + params.IdentityBaseGas
}
func (c *dataCopy) Run(in []byte) ([]byte, error) {
	return in, nil
}

// bigModExp implements a native big integer exponential modular operation.
type bigModExp struct{}

// RequiredGas returns the gas required to execute the pre-compiled contract.
func (c *bigModExp) RequiredGas(input []byte) uint64 {
	// Pad the input with zeroes to the minimum size to read the field lengths
	input = common.RightPadBytes(input, 96)

	var (
		baseLen = new(big.Int).SetBytes(input[:32])
		expLen  = new(big.Int).SetBytes(input[32:64])
		modLen  = new(big.Int).SetBytes(input[64:96])
	)
	input = input[96:]

	// Retrieve the head 32 bytes of exp for the adjusted exponent length
	var expHead *big.Int
	if big.NewInt(int64(len(input))).Cmp(baseLen) <= 0 {
		expHead = new(big.Int)
	} else {
		offset := int(baseLen.Uint64())

		input = common.RightPadBytes(input, offset+32)
		if expLen.Cmp(big.NewInt(32)) > 0 {
			expHead = new(big.Int).SetBytes(input[offset : offset+32])
		} else {
			expHead = new(big.Int).SetBytes(input[offset : offset+int(expLen.Uint64())])
		}
	}
	// Calculate the adjusted exponent length
	var msb int
	if bitlen := expHead.BitLen(); bitlen > 0 {
		msb = bitlen - 1
	}
	adjExpLen := new(big.Int)
	if expLen.Cmp(big.NewInt(32)) > 0 {
		adjExpLen.Sub(expLen, big.NewInt(32))
		adjExpLen.Mul(big.NewInt(8), adjExpLen)
	}
	adjExpLen.Add(adjExpLen, big.NewInt(int64(msb)))

	// Calculate the gas cost of the operation
	gas := new(big.Int).Set(math.BigMax(modLen, baseLen))
	switch {
	case gas.Cmp(big.NewInt(64)) <= 0:
		gas.Mul(gas, gas)
	case gas.Cmp(big.NewInt(1024)) <= 0:
		gas = new(big.Int).Add(
			new(big.Int).Div(new(big.Int).Mul(gas, gas), big.NewInt(4)),
			new(big.Int).Sub(new(big.Int).Mul(big.NewInt(96), gas), big.NewInt(3072)),
		)
	default:
		gas = new(big.Int).Add(
			new(big.Int).Div(new(big.Int).Mul(gas, gas), big.NewInt(16)),
			new(big.Int).Sub(new(big.Int).Mul(big.NewInt(480), gas), big.NewInt(199680)),
		)
	}
	gas.Mul(gas, math.BigMax(adjExpLen, big.NewInt(1)))
	gas.Div(gas, new(big.Int).SetUint64(params.ModExpQuadCoeffDiv))

	if gas.BitLen() > 64 {
		return math.MaxUint64
	}
	return gas.Uint64()
}

func (c *bigModExp) Run(input []byte) ([]byte, error) {
	// Pad the input with zeroes to the minimum size to read the field lengths
	input = common.RightPadBytes(input, 96)

	var (
		baseLen = new(big.Int).SetBytes(input[:32]).Uint64()
		expLen  = new(big.Int).SetBytes(input[32:64]).Uint64()
		modLen  = new(big.Int).SetBytes(input[64:96]).Uint64()
	)
	input = input[96:]

	// Pad the input with zeroes to the minimum size to read the field contents
	input = common.RightPadBytes(input, int(baseLen+expLen+modLen))

	var (
		base = new(big.Int).SetBytes(input[:baseLen])
		exp  = new(big.Int).SetBytes(input[baseLen : baseLen+expLen])
		mod  = new(big.Int).SetBytes(input[baseLen+expLen : baseLen+expLen+modLen])
	)
	if mod.BitLen() == 0 {
		// Modulo 0 is undefined, return zero
		return common.LeftPadBytes([]byte{}, int(modLen)), nil
	}
	return common.LeftPadBytes(base.Exp(base, exp, mod).Bytes(), int(modLen)), nil
}

var (
	// errNotOnCurve is returned if a point being unmarshalled as a bn256 elliptic
	// curve point is not on the curve.
	errNotOnCurve = errors.New("point not on elliptic curve")

	// errInvalidCurvePoint is returned if a point being unmarshalled as a bn256
	// elliptic curve point is invalid.
	errInvalidCurvePoint = errors.New("invalid elliptic curve point")
)

// newCurvePoint unmarshals a binary blob into a bn256 elliptic curve point,
// returning it, or an error if the point is invalid.
func newCurvePoint(blob []byte) (*bn256.G1, error) {
	p, onCurve := new(bn256.G1).Unmarshal(blob)
	if !onCurve {
		return nil, errNotOnCurve
	}
	gx, gy, _, _ := p.CurvePoints()
	if gx.Cmp(bn256.P) >= 0 || gy.Cmp(bn256.P) >= 0 {
		return nil, errInvalidCurvePoint
	}
	return p, nil
}

// newTwistPoint unmarshals a binary blob into a bn256 elliptic curve point,
// returning it, or an error if the point is invalid.
func newTwistPoint(blob []byte) (*bn256.G2, error) {
	p, onCurve := new(bn256.G2).Unmarshal(blob)
	if !onCurve {
		return nil, errNotOnCurve
	}
	x2, y2, _, _ := p.CurvePoints()
	if x2.Real().Cmp(bn256.P) >= 0 || x2.Imag().Cmp(bn256.P) >= 0 ||
		y2.Real().Cmp(bn256.P) >= 0 || y2.Imag().Cmp(bn256.P) >= 0 {
		return nil, errInvalidCurvePoint
	}
	return p, nil
}

// bn256Add implements a native elliptic curve point addition.
type bn256Add struct{}

// RequiredGas returns the gas required to execute the pre-compiled contract.
func (c *bn256Add) RequiredGas(input []byte) uint64 {
	return params.Bn256AddGas
}

func (c *bn256Add) Run(input []byte) ([]byte, error) {
	// Ensure we have enough data to operate on
	input = common.RightPadBytes(input, 128)

	x, err := newCurvePoint(input[:64])
	if err != nil {
		return nil, err
	}
	y, err := newCurvePoint(input[64:128])
	if err != nil {
		return nil, err
	}
	x.Add(x, y)
	return x.Marshal(), nil
}

// bn256ScalarMul implements a native elliptic curve scalar multiplication.
type bn256ScalarMul struct{}

// RequiredGas returns the gas required to execute the pre-compiled contract.
func (c *bn256ScalarMul) RequiredGas(input []byte) uint64 {
	return params.Bn256ScalarMulGas
}

func (c *bn256ScalarMul) Run(input []byte) ([]byte, error) {
	// Ensure we have enough data to operate on
	input = common.RightPadBytes(input, 96)

	p, err := newCurvePoint(input[:64])
	if err != nil {
		return nil, err
	}
	p.ScalarMult(p, new(big.Int).SetBytes(input[64:96]))
	return p.Marshal(), nil
}

var (
	// true32Byte is returned if the bn256 pairing check succeeds.
	true32Byte = []byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1}

	// false32Byte is returned if the bn256 pairing check fails.
	false32Byte = make([]byte, 32)

	// errBadPairingInput is returned if the bn256 pairing input is invalid.
	errBadPairingInput = errors.New("bad elliptic curve pairing size")
)

// bn256Pairing implements a pairing pre-compile for the bn256 curve
type bn256Pairing struct{}

// RequiredGas returns the gas required to execute the pre-compiled contract.
func (c *bn256Pairing) RequiredGas(input []byte) uint64 {
	return params.Bn256PairingBaseGas + uint64(len(input)/192)*params.Bn256PairingPerPointGas
}

func (c *bn256Pairing) Run(input []byte) ([]byte, error) {
	// Handle some corner cases cheaply
	if len(input)%192 > 0 {
		return nil, errBadPairingInput
	}
	// Convert the input into a set of coordinates
	var (
		cs []*bn256.G1
		ts []*bn256.G2
	)
	for i := 0; i < len(input); i += 192 {
		c, err := newCurvePoint(input[i : i+64])
		if err != nil {
			return nil, err
		}
		t, err := newTwistPoint(input[i+64 : i+192])
		if err != nil {
			return nil, err
		}
		cs = append(cs, c)
		ts = append(ts, t)
	}
	// Execute the pairing checks and return the results
	ok := bn256.PairingCheck(cs, ts)
	if ok {
		return true32Byte, nil
	}
	return false32Byte, nil
}