package ante

import (
	"math/big"

	sdk "github.com/cosmos/cosmos-sdk/types"
	sdkerrors "github.com/cosmos/cosmos-sdk/types/errors"
	authante "github.com/cosmos/cosmos-sdk/x/auth/ante"

	evmtypes "github.com/cosmos/ethermint/x/evm/types"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/core"
	ethtypes "github.com/ethereum/go-ethereum/core/types"
)

// EVMKeeper defines the expected keeper interface used on the Eth AnteHandler
type EVMKeeper interface {
	ChainID() *big.Int
	GetParams(ctx sdk.Context) evmtypes.Params
	GetChainConfig(ctx sdk.Context) (evmtypes.ChainConfig, bool)
	WithContext(ctx sdk.Context)
	ResetRefundTransient(ctx sdk.Context)
}

// EthSigVerificationDecorator validates an ethereum signature
type EthSigVerificationDecorator struct {
	evmKeeper EVMKeeper
}

// NewEthSigVerificationDecorator creates a new EthSigVerificationDecorator
func NewEthSigVerificationDecorator(ek EVMKeeper) EthSigVerificationDecorator {
	return EthSigVerificationDecorator{
		evmKeeper: ek,
	}
}

// AnteHandle validates checks that the registered chain id is the same as the one on the message, and
// that the signer address matches the one defined on the message.
func (esvd EthSigVerificationDecorator) AnteHandle(ctx sdk.Context, tx sdk.Tx, simulate bool, next sdk.AnteHandler) (newCtx sdk.Context, err error) {
	// no need to verify signatures on recheck tx
	if ctx.IsReCheckTx() {
		return next(ctx, tx, simulate)
	}

	// get and set account must be called with an infinite gas meter in order to prevent
	// additional gas from being deducted.
	infCtx := ctx.WithGasMeter(sdk.NewInfiniteGasMeter())

	chainID := esvd.evmKeeper.ChainID()

	config, found := esvd.evmKeeper.GetChainConfig(infCtx)
	if !found {
		return ctx, evmtypes.ErrChainConfigNotFound
	}

	ethCfg := config.EthereumConfig(chainID)
	blockNum := big.NewInt(ctx.BlockHeight())
	signer := ethtypes.MakeSigner(ethCfg, blockNum)

	for _, msg := range tx.GetMsgs() {
		msgEthTx, ok := msg.(*evmtypes.MsgEthereumTx)
		if !ok {
			return ctx, sdkerrors.Wrapf(sdkerrors.ErrUnknownRequest, "invalid transaction type %T, expected %T", tx, &evmtypes.MsgEthereumTx{})
		}

		if _, err := signer.Sender(msgEthTx.AsTransaction()); err != nil {
			return ctx, sdkerrors.Wrap(sdkerrors.ErrorInvalidSigner, err.Error())
		}
	}

	return next(ctx, tx, simulate)
}

// EthAccountVerificationDecorator validates an account balance checks
type EthAccountVerificationDecorator struct {
	ak         AccountKeeper
	bankKeeper BankKeeper
	evmKeeper  EVMKeeper
}

// NewEthAccountVerificationDecorator creates a new EthAccountVerificationDecorator
func NewEthAccountVerificationDecorator(ak AccountKeeper, bankKeeper BankKeeper, ek EVMKeeper) EthAccountVerificationDecorator {
	return EthAccountVerificationDecorator{
		ak:         ak,
		bankKeeper: bankKeeper,
		evmKeeper:  ek,
	}
}

// AnteHandle validates the signature and returns sender address
func (avd EthAccountVerificationDecorator) AnteHandle(ctx sdk.Context, tx sdk.Tx, simulate bool, next sdk.AnteHandler) (newCtx sdk.Context, err error) {
	if !ctx.IsCheckTx() {
		return next(ctx, tx, simulate)
	}

	// get and set account must be called with an infinite gas meter in order to prevent
	// additional gas from being deducted.
	infCtx := ctx.WithGasMeter(sdk.NewInfiniteGasMeter())

	evmDenom := avd.evmKeeper.GetParams(infCtx).EvmDenom

	for _, msg := range tx.GetMsgs() {
		msgEthTx, ok := msg.(*evmtypes.MsgEthereumTx)
		if !ok {
			return ctx, sdkerrors.Wrapf(sdkerrors.ErrUnknownRequest, "invalid transaction type %T, expected %T", tx, &evmtypes.MsgEthereumTx{})
		}

		// sender address should be in the tx cache from the previous AnteHandle call
		from := msgEthTx.GetFrom()
		if from.Empty() {
			return ctx, sdkerrors.Wrapf(sdkerrors.ErrInvalidAddress, "from address cannot be empty")
		}

		acc := avd.ak.GetAccount(infCtx, from)
		if acc == nil {
			_ = avd.ak.NewAccountWithAddress(infCtx, from)
		}

		// validate sender has enough funds to pay for gas cost
		balance := avd.bankKeeper.GetBalance(infCtx, from, evmDenom)
		if balance.Amount.BigInt().Cmp(msgEthTx.Cost()) < 0 {
			return ctx, sdkerrors.Wrapf(
				sdkerrors.ErrInsufficientFunds,
				"sender balance < tx gas cost (%s < %s%s)", balance.String(), msgEthTx.Cost().String(), evmDenom,
			)
		}
	}

	return next(ctx, tx, simulate)
}

// EthNonceVerificationDecorator checks that the account nonce from the transaction matches
// the sender account sequence.
type EthNonceVerificationDecorator struct {
	ak AccountKeeper
}

// NewEthNonceVerificationDecorator creates a new EthNonceVerificationDecorator
func NewEthNonceVerificationDecorator(ak AccountKeeper) EthNonceVerificationDecorator {
	return EthNonceVerificationDecorator{
		ak: ak,
	}
}

// AnteHandle validates that the transaction nonce is valid (equivalent to the sender account’s
// current nonce).
func (nvd EthNonceVerificationDecorator) AnteHandle(ctx sdk.Context, tx sdk.Tx, simulate bool, next sdk.AnteHandler) (newCtx sdk.Context, err error) {
	// no need to check the nonce on ReCheckTx
	if ctx.IsReCheckTx() {
		return next(ctx, tx, simulate)
	}

	// get and set account must be called with an infinite gas meter in order to prevent
	// additional gas from being deducted.
	infCtx := ctx.WithGasMeter(sdk.NewInfiniteGasMeter())

	for _, msg := range tx.GetMsgs() {
		msgEthTx, ok := msg.(*evmtypes.MsgEthereumTx)
		if !ok {
			return ctx, sdkerrors.Wrapf(sdkerrors.ErrUnknownRequest, "invalid transaction type %T, expected %T", tx, &evmtypes.MsgEthereumTx{})
		}

		// sender address should be in the tx cache from the previous AnteHandle call
		seq, err := nvd.ak.GetSequence(infCtx, msgEthTx.GetFrom())
		if err != nil {
			return ctx, err
		}

		// if multiple transactions are submitted in succession with increasing nonces,
		// all will be rejected except the first, since the first needs to be included in a block
		// before the sequence increments
		if msgEthTx.Data.Nonce != seq {
			return ctx, sdkerrors.Wrapf(
				sdkerrors.ErrInvalidSequence,
				"invalid nonce; got %d, expected %d", msgEthTx.Data.Nonce, seq,
			)
		}
	}

	return next(ctx, tx, simulate)
}

// EthGasConsumeDecorator validates enough intrinsic gas for the transaction and
// gas consumption.
type EthGasConsumeDecorator struct {
	ak         AccountKeeper
	bankKeeper BankKeeper
	evmKeeper  EVMKeeper
}

// NewEthGasConsumeDecorator creates a new EthGasConsumeDecorator
func NewEthGasConsumeDecorator(ak AccountKeeper, bankKeeper BankKeeper, ek EVMKeeper) EthGasConsumeDecorator {
	return EthGasConsumeDecorator{
		ak:         ak,
		bankKeeper: bankKeeper,
		evmKeeper:  ek,
	}
}

// AnteHandle validates that the Ethereum tx message has enough to cover intrinsic gas
// (during CheckTx only) and that the sender has enough balance to pay for the gas cost.
//
// Intrinsic gas for a transaction is the amount of gas
// that the transaction uses before the transaction is executed. The gas is a
// constant value of 21000 plus any cost inccured by additional bytes of data
// supplied with the transaction.
func (egcd EthGasConsumeDecorator) AnteHandle(ctx sdk.Context, tx sdk.Tx, simulate bool, next sdk.AnteHandler) (newCtx sdk.Context, err error) {
	// get and set account must be called with an infinite gas meter in order to prevent
	// additional gas from being deducted.
	infCtx := ctx.WithGasMeter(sdk.NewInfiniteGasMeter())

	if len(tx.GetMsgs()) != 1 {
		return ctx, sdkerrors.Wrapf(sdkerrors.ErrInvalidRequest, "only 1 ethereum msg supported per tx, got %d", len(tx.GetMsgs()))
	}

	// reset the refund gas value for the current transaction
	egcd.evmKeeper.ResetRefundTransient(infCtx)

	config, found := egcd.evmKeeper.GetChainConfig(infCtx)
	if !found {
		return ctx, evmtypes.ErrChainConfigNotFound
	}

	ethCfg := config.EthereumConfig(egcd.evmKeeper.ChainID())

	blockHeight := big.NewInt(ctx.BlockHeight())
	homestead := ethCfg.IsHomestead(blockHeight)
	istanbul := ethCfg.IsIstanbul(blockHeight)

	for _, msg := range tx.GetMsgs() {
		msgEthTx, ok := msg.(*evmtypes.MsgEthereumTx)
		if !ok {
			return ctx, sdkerrors.Wrapf(sdkerrors.ErrUnknownRequest, "invalid transaction type %T, expected %T", tx, &evmtypes.MsgEthereumTx{})
		}

		isContractCreation := msgEthTx.To() == nil

		// fetch sender account from signature
		signerAcc, err := authante.GetSignerAcc(infCtx, egcd.ak, msgEthTx.GetFrom())
		if err != nil {
			return ctx, err
		}

		gasLimit := msgEthTx.GetGas()

		var accessList ethtypes.AccessList
		if msgEthTx.Data.Accesses != nil {
			accessList = *msgEthTx.Data.Accesses.ToEthAccessList()
		}

		intrinsicGas, err := core.IntrinsicGas(msgEthTx.Data.Input, accessList, isContractCreation, homestead, istanbul)
		if err != nil {
			return ctx, sdkerrors.Wrap(err, "failed to compute intrinsic gas cost")
		}

		// intrinsic gas verification during CheckTx
		if ctx.IsCheckTx() && gasLimit < intrinsicGas {
			return ctx, sdkerrors.Wrapf(sdkerrors.ErrOutOfGas, "gas limit too low: %d (gas limit) < %d (intrinsic gas)", gasLimit, intrinsicGas)
		}

		// Cost calculates the fees paid to validators based on gas limit and price
		cost := msgEthTx.Fee() // fee = gas limit * gas price

		evmDenom := egcd.evmKeeper.GetParams(infCtx).EvmDenom
		feeAmt := sdk.Coins{sdk.NewCoin(evmDenom, sdk.NewIntFromBigInt(cost))}

		// deduct the full gas cost from the user balance
		if err := authante.DeductFees(egcd.bankKeeper, infCtx, signerAcc, feeAmt); err != nil {
			return ctx, err
		}

		// consume intrinsic gas for the current transaction. After runTx is executed on Baseapp, the
		// application will consume gas from the block gas pool.
		ctx.GasMeter().ConsumeGas(intrinsicGas, "intrinsic gas")
	}

	// generate a copy of the gas pool (i.e block gas meter) to see if we've run out of gas for this block
	// if current gas consumed is greater than the limit, this funcion panics and the error is recovered on the Baseapp
	gasPool := sdk.NewGasMeter(ctx.BlockGasMeter().Limit())
	gasPool.ConsumeGas(ctx.GasMeter().GasConsumedToLimit(), "gas pool check")

	// we know that we have enough gas on the pool to cover the intrinsic gas
	// set up the updated context to the evm Keeper
	egcd.evmKeeper.WithContext(ctx)
	return next(ctx, tx, simulate)
}

// EthIncrementSenderSequenceDecorator increments the sequence of the signers. The
// main difference with the SDK's IncrementSequenceDecorator is that the MsgEthereumTx
// doesn't implement the SigVerifiableTx interface.
//
// CONTRACT: must be called after msg.VerifySig in order to cache the sender address.
type EthIncrementSenderSequenceDecorator struct {
	ak AccountKeeper
}

// NewEthIncrementSenderSequenceDecorator creates a new EthIncrementSenderSequenceDecorator.
func NewEthIncrementSenderSequenceDecorator(ak AccountKeeper) EthIncrementSenderSequenceDecorator {
	return EthIncrementSenderSequenceDecorator{
		ak: ak,
	}
}

// AnteHandle handles incrementing the sequence of the sender.
func (issd EthIncrementSenderSequenceDecorator) AnteHandle(ctx sdk.Context, tx sdk.Tx, simulate bool, next sdk.AnteHandler) (sdk.Context, error) {
	// get and set account must be called with an infinite gas meter in order to prevent
	// additional gas from being deducted.
	infCtx := ctx.WithGasMeter(sdk.NewInfiniteGasMeter())

	for _, msg := range tx.GetMsgs() {
		// increment sequence of all signers
		for _, addr := range msg.GetSigners() {
			acc := issd.ak.GetAccount(infCtx, addr)
			if acc == nil {
				return ctx, sdkerrors.Wrapf(
					sdkerrors.ErrUnknownAddress,
					"account %s (%s) is nil", common.BytesToAddress(addr.Bytes()), addr,
				)
			}

			if err := acc.SetSequence(acc.GetSequence() + 1); err != nil {
				return ctx, err
			}

			issd.ak.SetAccount(infCtx, acc)
		}
	}

	// set the original gas meter
	return next(ctx, tx, simulate)
}