// Copyright Fuzamei Corp. 2018 All Rights Reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package runtime

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

	"github.com/33cn/plugin/plugin/dapp/evm/executor/vm/common"
	"github.com/33cn/plugin/plugin/dapp/evm/executor/vm/common/crypto"
	"github.com/33cn/plugin/plugin/dapp/evm/executor/vm/params"

	"github.com/33cn/plugin/plugin/dapp/evm/executor/vm/model"
	"golang.org/x/crypto/ripemd160"
)

// PrecompiledContract 系统内置合约实现的接口，只包含两个操作：
// 1 根据合约自身逻辑和入参，计算所需Gas；
// 2 执行合约。
type PrecompiledContract interface {
	// 计算当前合约执行需要消耗的Gas
	RequiredGas(input []byte) uint64

	// 执行预编译的合约固定逻辑，input为入参
	Run(input []byte) ([]byte, error)
}

// PrecompiledContractsByzantium chain33平台支持君士坦丁堡版本支持的所有预编译合约指令，并从此版本开始同步支持EVM黄皮书中的新增指令；
// 保存拜占庭版本支持的所有预编译合约（包括之前版本的合约）；
// 后面如果有硬分叉，需要在此处考虑分叉逻辑，根据区块高度分别处理；
// 下面的8个预编译指令，直接引用go-ethereum中的EVM实现
var PrecompiledContractsByzantium = 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{},

	// FIXME 这里还需要依赖EVM包装过的bn256包（common.crypto.bn256），没法使用原生bn256，后继需要优化为使用原生bn256
	// 难度比较大，优先级放低
	common.BytesToAddress([]byte{8}): &bn256Pairing{},
}

// RunPrecompiledContract 调用预编译的合约逻辑并返回结果
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, model.ErrOutOfGas
}

// 预编译合约 ECRECOVER 椭圆曲线算法支持
type ecrecover struct{}

// RequiredGas 需要消耗多少Gas
func (c *ecrecover) RequiredGas(input []byte) uint64 {
	return params.EcrecoverGas
}

// Run 运算
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 !common.AllZero(input[32:63]) || !crypto.ValidateSignatureValues(r, s) {
		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
}

// Run run
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
}

// Run run
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
}

// Run run
func (c *dataCopy) Run(in []byte) ([]byte, error) {
	return in, nil
}

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

var (
	big1      = big.NewInt(1)
	big4      = big.NewInt(4)
	big8      = big.NewInt(8)
	big16     = big.NewInt(16)
	big32     = big.NewInt(32)
	big64     = big.NewInt(64)
	big96     = big.NewInt(96)
	big480    = big.NewInt(480)
	big1024   = big.NewInt(1024)
	big3072   = big.NewInt(3072)
	big199680 = big.NewInt(199680)
)

// RequiredGas Returns the gas required to Execute the pre-compiled contract.
func (c *bigModExp) RequiredGas(input []byte) uint64 {
	var (
		baseLen = new(big.Int).SetBytes(common.GetData(input, 0, 32))
		expLen  = new(big.Int).SetBytes(common.GetData(input, 32, 32))
		modLen  = new(big.Int).SetBytes(common.GetData(input, 64, 32))
	)
	if len(input) > 96 {
		input = input[96:]
	} else {
		input = input[:0]
	}
	// 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 {
		if expLen.Cmp(big32) > 0 {
			expHead = new(big.Int).SetBytes(common.GetData(input, baseLen.Uint64(), 32))
		} else {
			expHead = new(big.Int).SetBytes(common.GetData(input, baseLen.Uint64(), 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(big32) > 0 {
		adjExpLen.Sub(expLen, big32)
		adjExpLen.Mul(big8, adjExpLen)
	}
	adjExpLen.Add(adjExpLen, big.NewInt(int64(msb)))

	// Calculate the gas cost of the Operation
	gas := new(big.Int).Set(common.BigMax(modLen, baseLen))
	switch {
	case gas.Cmp(big64) <= 0:
		gas.Mul(gas, gas)
	case gas.Cmp(big1024) <= 0:
		gas = new(big.Int).Add(
			new(big.Int).Div(new(big.Int).Mul(gas, gas), big4),
			new(big.Int).Sub(new(big.Int).Mul(big96, gas), big3072),
		)
	default:
		gas = new(big.Int).Add(
			new(big.Int).Div(new(big.Int).Mul(gas, gas), big16),
			new(big.Int).Sub(new(big.Int).Mul(big480, gas), big199680),
		)
	}
	gas.Mul(gas, common.BigMax(adjExpLen, big1))
	gas.Div(gas, new(big.Int).SetUint64(params.ModExpQuadCoeffDiv))

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

// Run run
func (c *bigModExp) Run(input []byte) ([]byte, error) {
	var (
		baseLen = new(big.Int).SetBytes(common.GetData(input, 0, 32)).Uint64()
		expLen  = new(big.Int).SetBytes(common.GetData(input, 32, 32)).Uint64()
		modLen  = new(big.Int).SetBytes(common.GetData(input, 64, 32)).Uint64()
	)
	if len(input) > 96 {
		input = input[96:]
	} else {
		input = input[:0]
	}
	// Handle a special case when both the base and mod length is zero
	if baseLen == 0 && modLen == 0 {
		return []byte{}, nil
	}
	// Retrieve the operands and Execute the exponentiation
	var (
		base = new(big.Int).SetBytes(common.GetData(input, 0, baseLen))
		exp  = new(big.Int).SetBytes(common.GetData(input, baseLen, expLen))
		mod  = new(big.Int).SetBytes(common.GetData(input, 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
}
