package keeper

import (
	"errors"
	"math/big"
	"os"
	"time"

	"github.com/palantir/stacktrace"
	tmtypes "github.com/tendermint/tendermint/types"

	"github.com/cosmos/cosmos-sdk/telemetry"
	sdk "github.com/cosmos/cosmos-sdk/types"
	sdkerrors "github.com/cosmos/cosmos-sdk/types/errors"
	authtypes "github.com/cosmos/cosmos-sdk/x/auth/types"

	ethermint "github.com/tharsis/ethermint/types"
	"github.com/tharsis/ethermint/x/evm/types"

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

// NewEVM generates an ethereum VM from the provided Message fields and the ChainConfig.
func (k *Keeper) NewEVM(msg core.Message, config *params.ChainConfig) *vm.EVM {
	blockCtx := vm.BlockContext{
		CanTransfer: core.CanTransfer,
		Transfer:    core.Transfer,
		GetHash:     k.GetHashFn(),
		Coinbase:    common.Address{}, // there's no beneficiary since we're not mining
		GasLimit:    ethermint.BlockGasLimit(k.ctx),
		BlockNumber: big.NewInt(k.ctx.BlockHeight()),
		Time:        big.NewInt(k.ctx.BlockHeader().Time.Unix()),
		Difficulty:  big.NewInt(0), // unused. Only required in PoW context
	}

	txCtx := core.NewEVMTxContext(msg)
	vmConfig := k.VMConfig()

	return vm.NewEVM(blockCtx, txCtx, k, config, vmConfig)
}

// VMConfig creates an EVM configuration from the module parameters and the debug setting.
// The config generated uses the default JumpTable from the EVM.
func (k Keeper) VMConfig() vm.Config {
	params := k.GetParams(k.ctx)

	return vm.Config{
		Debug:       k.debug,
		Tracer:      vm.NewJSONLogger(&vm.LogConfig{Debug: k.debug}, os.Stderr), // TODO: consider using the Struct Logger too
		NoRecursion: false,                                                      // TODO: consider disabling recursion though params
		ExtraEips:   params.EIPs(),
	}
}

// GetHashFn implements vm.GetHashFunc for Ethermint. It handles 3 cases:
//  1. The requested height matches the current height from context (and thus same epoch number)
//  2. The requested height is from an previous height from the same chain epoch
//  3. The requested height is from a height greater than the latest one
func (k Keeper) GetHashFn() vm.GetHashFunc {
	return func(height uint64) common.Hash {
		h := int64(height)
		switch {
		case k.ctx.BlockHeight() == h:
			// Case 1: The requested height matches the one from the context so we can retrieve the header
			// hash directly from the context.
			return common.BytesToHash(k.ctx.HeaderHash())

		case k.ctx.BlockHeight() > h:
			// Case 2: if the chain is not the current height we need to retrieve the hash from the store for the
			// current chain epoch. This only applies if the current height is greater than the requested height.
			histInfo, found := k.stakingKeeper.GetHistoricalInfo(k.ctx, h)
			if !found {
				k.Logger(k.ctx).Debug("historical info not found", "height", h)
				return common.Hash{}
			}

			header, err := tmtypes.HeaderFromProto(&histInfo.Header)
			if err != nil {
				k.Logger(k.ctx).Error("failed to cast tendermint header from proto", "error", err)
				return common.Hash{}
			}

			return common.BytesToHash(header.Hash())
		default:
			// Case 3: heights greater than the current one returns an empty hash.
			return common.Hash{}
		}
	}
}

// ApplyTransaction runs and attempts to perform a state transition with the given transaction (i.e Message), that will
// only be persisted to the underlying KVStore if the transaction does not error.
//
// Gas tracking
//
// Ethereum consumes gas according to the EVM opcodes instead of general reads and writes to store. Because of this, the
// state transition needs to ignore the SDK gas consumption mechanism defined by the GasKVStore and instead consume the
// amount of gas used by the VM execution. The amount of gas used is tracked by the EVM and returned in the execution
// result.
//
// Prior to the execution, the starting tx gas meter is saved and replaced with an infinite gas meter in a new context
// in order to ignore the SDK gas consumption config values (read, write, has, delete).
// After the execution, the gas used from the message execution will be added to the starting gas consumed, taking into
// consideration the amount of gas returned. Finally, the context is updated with the EVM gas consumed value prior to
// returning.
//
// For relevant discussion see: https://github.com/cosmos/cosmos-sdk/discussions/9072
func (k *Keeper) ApplyTransaction(tx *ethtypes.Transaction) (*types.MsgEthereumTxResponse, error) {
	defer telemetry.ModuleMeasureSince(types.ModuleName, time.Now(), types.MetricKeyTransitionDB)

	gasMeter := k.ctx.GasMeter() // tx gas meter

	// ignore gas consumption costs
	infCtx := k.ctx.WithGasMeter(sdk.NewInfiniteGasMeter())

	cfg, found := k.GetChainConfig(infCtx)
	if !found {
		return nil, stacktrace.Propagate(types.ErrChainConfigNotFound, "configuration not found")
	}
	ethCfg := cfg.EthereumConfig(k.eip155ChainID)

	// get the latest signer according to the chain rules from the config
	signer := ethtypes.MakeSigner(ethCfg, big.NewInt(k.ctx.BlockHeight()))

	msg, err := tx.AsMessage(signer)
	if err != nil {
		return nil, stacktrace.Propagate(err, "failed to return ethereum transaction as core message")
	}

	evm := k.NewEVM(msg, ethCfg)

	k.IncreaseTxIndexTransient()

	// set the original gas meter to apply the message and perform the state transition

	k.WithContext(k.ctx.WithGasMeter(gasMeter))
	// create an ethereum StateTransition instance and run TransitionDb
	res, err := k.ApplyMessage(evm, msg, ethCfg)
	if err != nil {
		return nil, stacktrace.Propagate(err, "failed to apply ethereum core message")
	}

	// NOTE: we set up the transaction hash from tendermint as it is the format expected by the application:
	// Remove once hashing is fixed on Tendermint. See https://github.com/tendermint/tendermint/issues/6539
	txHash := common.BytesToHash(tmtypes.Tx(k.ctx.TxBytes()).Hash())
	res.Hash = txHash.Hex()

	logs := k.GetTxLogs(txHash)
	res.Logs = types.NewLogsFromEth(logs)

	// update block bloom filter
	bloom := k.GetBlockBloomTransient()
	bloom.Or(bloom, big.NewInt(0).SetBytes(ethtypes.LogsBloom(logs)))
	k.SetBlockBloomTransient(bloom)

	return res, nil
}

// Gas consumption notes (write doc from this)

// gas = remaining gas = limit - consumed

// Gas consumption in ethereum:
// 0. Buy gas -> deduct gasLimit * gasPrice from user account
// 		0.1 leftover gas = gas limit
// 1. consume intrinsic gas
//   1.1 leftover gas = leftover gas - intrinsic gas
// 2. Exec vm functions by passing the gas (i.e remaining gas)
//   2.1 final leftover gas returned after spending gas from the opcodes jump tables
// 3. Refund amount =  max(gasConsumed / 2, gas refund), where gas refund is a local variable

// TODO: (@fedekunze) currently we consume the entire gas limit in the ante handler, so if a transaction fails
// the amount spent will be grater than the gas spent in an Ethereum tx (i.e here the leftover gas won't be refunded).

// ApplyMessage computes the new state by applying the given message against the existing state.
// If the message fails, the VM execution error with the reason will be returned to the client
// and the transaction won't be committed to the store.
//
// Reverted state
//
// The transaction is never "reverted" since there is no snapshot + rollback performed on the StateDB.
// Only successful transactions are written to the store during DeliverTx mode.
//
// Prechecks and Preprocessing
//
// All relevant state transition prechecks for the MsgEthereumTx are performed on the AnteHandler,
// prior to running the transaction against the state. The prechecks run are the following:
//
// 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
//
// The preprocessing steps performed by the AnteHandler are:
//
// 1. set up the initial access list (iff fork > Berlin)
func (k *Keeper) ApplyMessage(evm *vm.EVM, msg core.Message, cfg *params.ChainConfig) (*types.MsgEthereumTxResponse, error) {
	var (
		ret   []byte // return bytes from evm execution
		vmErr error  // vm errors do not effect consensus and are therefore not assigned to err
	)

	sender := vm.AccountRef(msg.From())
	contractCreation := msg.To() == nil

	// transaction gas meter (tracks limit and usage)
	gasConsumed := k.ctx.GasMeter().GasConsumed()
	leftoverGas := k.ctx.GasMeter().Limit() - k.ctx.GasMeter().GasConsumedToLimit()

	// NOTE: Since CRUD operations on the SDK store consume gas we need to set up an infinite gas meter so that we only consume
	// the gas used by the Ethereum message execution.
	// Not setting the infinite gas meter here would mean that we are incurring in additional gas costs
	k.WithContext(k.ctx.WithGasMeter(sdk.NewInfiniteGasMeter()))

	// NOTE: gas limit is the GasLimit defied in the message minus the Intrinsic Gas that has already been
	// consumed on the AnteHandler.

	// ensure gas is consistent during CheckTx
	if k.ctx.IsCheckTx() {
		if err := k.CheckGasConsumption(msg, cfg, gasConsumed, contractCreation); err != nil {
			return nil, stacktrace.Propagate(err, "gas consumption check failed during CheckTx")
		}
	}

	if contractCreation {
		ret, _, leftoverGas, vmErr = evm.Create(sender, msg.Data(), leftoverGas, msg.Value())
	} else {
		ret, leftoverGas, vmErr = evm.Call(sender, *msg.To(), msg.Data(), leftoverGas, msg.Value())
	}

	// refund gas prior to handling the vm error in order to set the updated gas meter
	if err := k.RefundGas(msg, leftoverGas); err != nil {
		return nil, stacktrace.Propagate(err, "failed to refund gas leftover gas to sender %s", msg.From())
	}

	if vmErr != nil {
		if errors.Is(vmErr, vm.ErrExecutionReverted) {
			// unpack the return data bytes from the err if the execution has been "reverted" on the VM
			return nil, stacktrace.Propagate(types.NewExecErrorWithReson(ret), "transaction reverted")
		}

		// wrap the VM error
		return nil, stacktrace.Propagate(sdkerrors.Wrap(types.ErrVMExecution, vmErr.Error()), "vm execution failed")
	}

	return &types.MsgEthereumTxResponse{
		Ret:      ret,
		Reverted: false,
	}, nil
}

// CheckGasConsumption verifies that the amount of gas consumed so far matches the intrinsic gas value.
func (k *Keeper) CheckGasConsumption(msg core.Message, cfg *params.ChainConfig, gasConsumed uint64, isContractCreation bool) error {
	height := big.NewInt(k.ctx.BlockHeight())
	homestead := cfg.IsHomestead(height)
	istanbul := cfg.IsIstanbul(height)

	intrinsicGas, err := core.IntrinsicGas(msg.Data(), msg.AccessList(), isContractCreation, homestead, istanbul)
	if err != nil {
		// should have already been checked on Ante Handler
		return stacktrace.Propagate(err, "intrinsic gas failed")
	}

	if intrinsicGas != gasConsumed {
		return sdkerrors.Wrapf(types.ErrInconsistentGas, "expected gas consumption to be %d (intrinsic gas only), got %d", intrinsicGas, gasConsumed)
	}

	return nil
}

// RefundGas transfers the leftover gas to the sender of the message, caped to half of the total gas
// consumed in the transaction. Additionally, the function sets the total gas consumed to the value
// returned by the EVM execution, thus ignoring the previous intrinsic gas inconsumed during in the
// AnteHandler.
func (k *Keeper) RefundGas(msg core.Message, leftoverGas uint64) error {
	if leftoverGas > msg.Gas() {
		return stacktrace.Propagate(
			sdkerrors.Wrapf(types.ErrInconsistentGas, "leftover gas cannot be greater than gas limit (%d > %d)", leftoverGas, msg.Gas()),
			"failed to update gas consumed after refund of leftover gas",
		)
	}

	gasConsumed := msg.Gas() - leftoverGas

	// Apply refund counter, capped to half of the used gas.
	refund := gasConsumed / 2
	availableRefund := k.GetRefund()
	if refund > availableRefund {
		refund = availableRefund
	}

	leftoverGas += refund

	if leftoverGas > msg.Gas() {
		return stacktrace.Propagate(
			sdkerrors.Wrapf(types.ErrInconsistentGas, "leftover gas cannot be greater than gas limit (%d > %d)", leftoverGas, msg.Gas()),
			"failed to update gas consumed after refund of %d gas", refund,
		)
	}

	gasConsumed = msg.Gas() - leftoverGas

	// Return EVM tokens for remaining gas, exchanged at the original rate.
	remaining := new(big.Int).Mul(new(big.Int).SetUint64(leftoverGas), msg.GasPrice())

	// ignore gas consumption
	infCtx := k.ctx.WithGasMeter(sdk.NewInfiniteGasMeter())

	switch remaining.Sign() {
	case -1:
		// negative refund errors
		return sdkerrors.Wrapf(types.ErrInvalidRefund, "refunded amount value cannot be negative %d", remaining.Int64())
	case 1:
		// positive amount refund
		params := k.GetParams(infCtx)
		refundedCoins := sdk.Coins{sdk.NewCoin(params.EvmDenom, sdk.NewIntFromBigInt(remaining))}

		// refund to sender from the fee collector module account, which is the escrow account in charge of collecting tx fees

		err := k.bankKeeper.SendCoinsFromModuleToAccount(infCtx, authtypes.FeeCollectorName, msg.From().Bytes(), refundedCoins)
		if err != nil {
			err = sdkerrors.Wrapf(sdkerrors.ErrInsufficientFunds, "fee collector account failed to refund fees: %s", err.Error())
			return stacktrace.Propagate(err, "failed to refund %d leftover gas (%s)", leftoverGas, refundedCoins.String())
		}
	default:
		// no refund, consume gas and update the tx gas meter
	}

	// set the gas consumed into the context with the new gas meter. This gas meter will have the
	// original gas limit defined in the msg and will consume the gas now that the amount has been
	// refunded
	gasMeter := sdk.NewGasMeter(msg.Gas())
	// NOTE: gas consumed will always be less than the limit
	gasMeter.ConsumeGas(gasConsumed, "update gas consumption after refund")
	k.WithContext(k.ctx.WithGasMeter(gasMeter))

	return nil
}