// 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 core

import (
	"fmt"
	"math"
	"math/big"

	"github.com/XinFinOrg/XDPoSChain/common"
	"github.com/XinFinOrg/XDPoSChain/core/types"
	"github.com/XinFinOrg/XDPoSChain/core/vm"
	"github.com/XinFinOrg/XDPoSChain/crypto"
	"github.com/XinFinOrg/XDPoSChain/params"
	"github.com/holiman/uint256"
)

var emptyCodeHash = crypto.Keccak256Hash(nil)

/*
The State Transitioning Model

A state transition is a change made when a transaction is applied to the current world state
The state transitioning model does all all the necessary work to work out a valid new state root.

1) Nonce handling
2) Pre pay gas
3) Create a new state object if the recipient is \0*32
4) Value transfer
== If contract creation ==

	4a) Attempt to run transaction data
	4b) If valid, use result as code for the new state object

== end ==
5) Run Script section
6) Derive new state root
*/
type StateTransition struct {
	gp         *GasPool
	msg        Message
	gas        uint64
	gasPrice   *big.Int
	gasFeeCap  *big.Int
	gasTipCap  *big.Int
	initialGas uint64
	value      *big.Int
	data       []byte
	state      vm.StateDB
	evm        *vm.EVM
}

// Message represents a message sent to a contract.
type Message interface {
	From() common.Address
	To() *common.Address

	GasPrice() *big.Int
	GasFeeCap() *big.Int
	GasTipCap() *big.Int
	Gas() uint64
	Value() *big.Int

	Nonce() uint64
	IsFake() bool
	Data() []byte
	BalanceTokenFee() *big.Int
	AccessList() types.AccessList
}

// ExecutionResult includes all output after executing given evm
// message no matter the execution itself is successful or not.
type ExecutionResult struct {
	UsedGas    uint64 // Total used gas but include the refunded gas
	Err        error  // Any error encountered during the execution(listed in core/vm/errors.go)
	ReturnData []byte // Returned data from evm(function result or data supplied with revert opcode)
}

// Failed returns the indicator whether the execution is successful or not
func (result *ExecutionResult) Failed() bool { return result.Err != nil }

// Return is a helper function to help caller distinguish between revert reason
// and function return. Return returns the data after execution if no error occurs.
func (result *ExecutionResult) Return() []byte {
	if result.Err != nil {
		return nil
	}
	return common.CopyBytes(result.ReturnData)
}

// Revert returns the concrete revert reason if the execution is aborted by `REVERT`
// opcode. Note the reason can be nil if no data supplied with revert opcode.
func (result *ExecutionResult) Revert() []byte {
	if result.Err != vm.ErrExecutionReverted {
		return nil
	}
	return common.CopyBytes(result.ReturnData)
}

// IntrinsicGas computes the 'intrinsic gas' for a message with the given data.
func IntrinsicGas(data []byte, accessList types.AccessList, isContractCreation, isHomestead bool, isEIP3860 bool) (uint64, error) {
	// Set the starting gas for the raw transaction
	var gas uint64
	if isContractCreation && isHomestead {
		gas = params.TxGasContractCreation
	} else {
		gas = params.TxGas
	}
	dataLen := uint64(len(data))
	// Bump the required gas by the amount of transactional data
	if dataLen > 0 {
		// Zero and non-zero bytes are priced differently
		var nz uint64
		for _, byt := range data {
			if byt != 0 {
				nz++
			}
		}
		// Make sure we don't exceed uint64 for all data combinations
		if (math.MaxUint64-gas)/params.TxDataNonZeroGas < nz {
			return 0, ErrGasUintOverflow
		}
		gas += nz * params.TxDataNonZeroGas

		z := dataLen - nz
		if (math.MaxUint64-gas)/params.TxDataZeroGas < z {
			return 0, ErrGasUintOverflow
		}
		gas += z * params.TxDataZeroGas

		if isContractCreation && isEIP3860 {
			lenWords := toWordSize(dataLen)
			if (math.MaxUint64-gas)/params.InitCodeWordGas < lenWords {
				return 0, ErrGasUintOverflow
			}
			gas += lenWords * params.InitCodeWordGas
		}
	}
	if accessList != nil {
		gas += uint64(len(accessList)) * params.TxAccessListAddressGas
		gas += uint64(accessList.StorageKeys()) * params.TxAccessListStorageKeyGas
	}
	return gas, nil
}

// toWordSize returns the ceiled word size required for init code payment calculation.
func toWordSize(size uint64) uint64 {
	if size > math.MaxUint64-31 {
		return math.MaxUint64/32 + 1
	}

	return (size + 31) / 32
}

// NewStateTransition initialises and returns a new state transition object.
func NewStateTransition(evm *vm.EVM, msg Message, gp *GasPool) *StateTransition {
	return &StateTransition{
		gp:        gp,
		evm:       evm,
		msg:       msg,
		gasPrice:  msg.GasPrice(),
		gasFeeCap: msg.GasFeeCap(),
		gasTipCap: msg.GasTipCap(),
		value:     msg.Value(),
		data:      msg.Data(),
		state:     evm.StateDB,
	}
}

// ApplyMessage computes the new state by applying the given message
// against the old state within the environment.
//
// ApplyMessage returns the bytes returned by any EVM execution (if it took place),
// the gas used (which includes gas refunds) and an error if it failed. An error always
// indicates a core error meaning that the message would always fail for that particular
// state and would never be accepted within a block.
func ApplyMessage(evm *vm.EVM, msg Message, gp *GasPool, owner common.Address) (*ExecutionResult, error) {
	return NewStateTransition(evm, msg, gp).TransitionDb(owner)
}

func (st *StateTransition) from() vm.AccountRef {
	f := st.msg.From()
	if !st.state.Exist(f) {
		st.state.CreateAccount(f)
	}
	return vm.AccountRef(f)
}

func (st *StateTransition) balanceTokenFee() *big.Int {
	return st.msg.BalanceTokenFee()
}

func (st *StateTransition) to() vm.AccountRef {
	if st.msg == nil {
		return vm.AccountRef{}
	}
	to := st.msg.To()
	if to == nil {
		return vm.AccountRef{} // contract creation
	}

	reference := vm.AccountRef(*to)
	if !st.state.Exist(*to) {
		st.state.CreateAccount(*to)
	}
	return reference
}

func (st *StateTransition) buyGas() error {
	mgval := new(big.Int).SetUint64(st.msg.Gas())
	mgval = mgval.Mul(mgval, st.gasPrice)
	balanceTokenFee := st.balanceTokenFee()
	if balanceTokenFee == nil {
		balanceCheck := mgval
		if st.gasFeeCap != nil {
			balanceCheck = new(big.Int).SetUint64(st.msg.Gas())
			balanceCheck = balanceCheck.Mul(balanceCheck, st.gasFeeCap)
			balanceCheck.Add(balanceCheck, st.value)
		}
		if have, want := st.state.GetBalance(st.msg.From()), balanceCheck; have.Cmp(want) < 0 {
			return fmt.Errorf("%w: address %v have %v want %v", ErrInsufficientFunds, st.msg.From().Hex(), have, want)
		}
	} else if balanceTokenFee.Cmp(mgval) < 0 {
		return ErrInsufficientFunds
	}
	if err := st.gp.SubGas(st.msg.Gas()); err != nil {
		return err
	}
	st.gas += st.msg.Gas()

	st.initialGas = st.msg.Gas()
	if balanceTokenFee == nil {
		st.state.SubBalance(st.msg.From(), mgval)
	}
	return nil
}

func (st *StateTransition) preCheck() error {
	// Only check transactions that are not fake
	msg := st.msg
	if !msg.IsFake() {
		// Make sure this transaction's nonce is correct.
		stNonce := st.state.GetNonce(msg.From())
		if msgNonce := msg.Nonce(); stNonce < msgNonce {
			return fmt.Errorf("%w: address %v, tx: %d state: %d", ErrNonceTooHigh,
				msg.From().Hex(), msgNonce, stNonce)
		} else if stNonce > msgNonce {
			return fmt.Errorf("%w: address %v, tx: %d state: %d", ErrNonceTooLow,
				msg.From().Hex(), msgNonce, stNonce)
		} else if stNonce+1 < stNonce {
			return fmt.Errorf("%w: address %v, nonce: %d", ErrNonceMax,
				msg.From().Hex(), stNonce)
		}
		// Make sure the sender is an EOA
		if codeHash := st.state.GetCodeHash(msg.From()); codeHash != emptyCodeHash && codeHash != (common.Hash{}) {
			return fmt.Errorf("%w: address %v, codehash: %s", ErrSenderNoEOA,
				msg.From().Hex(), codeHash)
		}
	}

	// Make sure that transaction gasFeeCap is greater than the baseFee (post london)
	if st.evm.ChainConfig().IsEIP1559(st.evm.Context.BlockNumber) {
		// Skip the checks if gas fields are zero and baseFee was explicitly disabled (eth_call)
		skipCheck := st.evm.Config.NoBaseFee && st.gasFeeCap.BitLen() == 0 && st.gasTipCap.BitLen() == 0
		if !skipCheck {
			if l := st.gasFeeCap.BitLen(); l > 256 {
				return fmt.Errorf("%w: address %v, maxFeePerGas bit length: %d", ErrFeeCapVeryHigh,
					msg.From().Hex(), l)
			}
			if l := st.gasTipCap.BitLen(); l > 256 {
				return fmt.Errorf("%w: address %v, maxPriorityFeePerGas bit length: %d", ErrTipVeryHigh,
					msg.From().Hex(), l)
			}
			if st.gasFeeCap.Cmp(st.gasTipCap) < 0 {
				return fmt.Errorf("%w: address %v, maxPriorityFeePerGas: %s, maxFeePerGas: %s", ErrTipAboveFeeCap,
					msg.From().Hex(), st.gasTipCap, st.gasFeeCap)
			}
			// This will panic if baseFee is nil, but basefee presence is verified
			// as part of header validation.
			if !types.IsSpecialTx(msg.To()) && st.gasFeeCap.Cmp(st.evm.Context.BaseFee) < 0 {
				return fmt.Errorf("%w: address %v, maxFeePerGas: %s baseFee: %s", ErrFeeCapTooLow,
					msg.From().Hex(), st.gasFeeCap, st.evm.Context.BaseFee)
			}
		}
	}
	return st.buyGas()
}

// TransitionDb will transition the state by applying the current message and
// returning the evm execution result with following fields.
//
//   - used gas:
//     total gas used (including gas being refunded)
//   - returndata:
//     the returned data from evm
//   - concrete execution error:
//     various **EVM** error which aborts the execution,
//     e.g. ErrOutOfGas, ErrExecutionReverted
//
// However if any consensus issue encountered, return the error directly with
// nil evm execution result.
func (st *StateTransition) TransitionDb(owner common.Address) (*ExecutionResult, error) {
	// First check this message satisfies all consensus rules before
	// applying the message. The rules include these clauses
	//
	// 1. the nonce of the message caller is correct
	// 2. caller has enough balance to cover transaction fee(gaslimit * gasprice)
	// 3. the amount of gas required is available in the block
	// 4. the purchased gas is enough to cover intrinsic usage
	// 5. there is no overflow when calculating intrinsic gas
	// 6. caller has enough balance to cover asset transfer for **topmost** call

	// Check clauses 1-3, buy gas if everything is correct
	if err := st.preCheck(); err != nil {
		return nil, err
	}

	var (
		msg              = st.msg
		sender           = st.from() // err checked in preCheck
		rules            = st.evm.ChainConfig().Rules(st.evm.Context.BlockNumber)
		homestead        = rules.IsHomestead
		eip3529          = rules.IsEIP1559
		contractCreation = msg.To() == nil
	)

	// Check clauses 4-5, subtract intrinsic gas if everything is correct
	gas, err := IntrinsicGas(st.data, st.msg.AccessList(), contractCreation, homestead, rules.IsEIP1559)
	if err != nil {
		return nil, err
	}
	if st.gas < gas {
		return nil, fmt.Errorf("%w: have %d, want %d", ErrIntrinsicGas, st.gas, gas)
	}
	st.gas -= gas

	// Check whether the init code size has been exceeded.
	if rules.IsEIP1559 && contractCreation && len(st.data) > params.MaxInitCodeSize {
		return nil, fmt.Errorf("%w: code size %v limit %v", ErrMaxInitCodeSizeExceeded, len(st.data), params.MaxInitCodeSize)
	}

	// Execute the preparatory steps for state transition which includes:
	// - prepare accessList(post-berlin)
	// - reset transient storage(eip 1153)
	st.state.Prepare(rules, msg.From(), st.evm.Context.Coinbase, msg.To(), vm.ActivePrecompiles(rules), msg.AccessList())

	// Check clause 6
	value, overflow := uint256.FromBig(msg.Value())
	if overflow {
		return nil, fmt.Errorf("%w: address %v", ErrInsufficientFundsForTransfer, msg.From().Hex())
	}
	if !value.IsZero() && !st.evm.Context.CanTransfer(st.state, msg.From(), value.ToBig()) {
		return nil, fmt.Errorf("%w: address %v", ErrInsufficientFundsForTransfer, msg.From().Hex())
	}

	var (
		ret   []byte
		vmerr error // vm errors do not effect consensus and are therefore not assigned to err
	)
	if contractCreation {
		ret, _, st.gas, vmerr = st.evm.Create(sender, st.data, st.gas, st.value)
	} else {
		// Increment the nonce for the next transaction
		st.state.SetNonce(sender.Address(), st.state.GetNonce(sender.Address())+1)
		ret, st.gas, vmerr = st.evm.Call(sender, st.to().Address(), st.data, st.gas, st.value)
	}
	if !eip3529 {
		// Before EIP-3529: refunds were capped to gasUsed / 2
		st.refundGas(params.RefundQuotient)
	} else {
		// After EIP-3529: refunds are capped to gasUsed / 5
		st.refundGas(params.RefundQuotientEIP3529)
	}

	if st.evm.Context.BlockNumber.Cmp(common.TIPTRC21Fee) > 0 {
		if (owner != common.Address{}) {
			st.state.AddBalance(owner, new(big.Int).Mul(new(big.Int).SetUint64(st.gasUsed()), st.gasPrice))
		}
	} else {
		effectiveTip := st.gasPrice
		if st.evm.ChainConfig().IsEIP1559(st.evm.Context.BlockNumber) {
			effectiveTip = new(big.Int).Sub(st.gasFeeCap, st.evm.Context.BaseFee)
			if effectiveTip.Cmp(st.gasTipCap) > 0 {
				effectiveTip = st.gasTipCap
			}
		}
		st.state.AddBalance(st.evm.Context.Coinbase, new(big.Int).Mul(new(big.Int).SetUint64(st.gasUsed()), effectiveTip))
	}

	return &ExecutionResult{
		UsedGas:    st.gasUsed(),
		Err:        vmerr,
		ReturnData: ret,
	}, nil
}

func (st *StateTransition) refundGas(refundQuotient uint64) {
	// Apply refund counter, capped to a refund quotient
	refund := st.gasUsed() / refundQuotient
	if refund > st.state.GetRefund() {
		refund = st.state.GetRefund()
	}
	st.gas += refund

	balanceTokenFee := st.balanceTokenFee()
	if balanceTokenFee == nil {
		from := st.from()
		// Return ETH for remaining gas, exchanged at the original rate.
		remaining := new(big.Int).Mul(new(big.Int).SetUint64(st.gas), st.gasPrice)
		st.state.AddBalance(from.Address(), remaining)
	}
	// Also return remaining gas to the block gas counter so it is
	// available for the next transaction.
	st.gp.AddGas(st.gas)
}

// gasUsed returns the amount of gas used up by the state transition.
func (st *StateTransition) gasUsed() uint64 {
	return st.initialGas - st.gas
}