mev-beta/pkg/arbitrum/gas.go

package arbitrum

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

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

	"github.com/fraktal/mev-beta/internal/logger"
	"github.com/fraktal/mev-beta/pkg/math"
)

// L2GasEstimator provides Arbitrum-specific gas estimation and optimization
type L2GasEstimator struct {
	client *ArbitrumClient
	logger *logger.Logger

	// L2 gas price configuration
	baseFeeMultiplier  float64
	priorityFeeMin     *big.Int
	priorityFeeMax     *big.Int
	gasLimitMultiplier float64
}

// GasEstimate represents an L2 gas estimate with detailed breakdown
type GasEstimate struct {
	GasLimit       uint64
	MaxFeePerGas   *big.Int
	MaxPriorityFee *big.Int
	L1DataFee      *big.Int
	L2ComputeFee   *big.Int
	TotalFee       *big.Int
	Confidence     float64 // 0-1 scale
}

// NewL2GasEstimator creates a new L2 gas estimator
func NewL2GasEstimator(client *ArbitrumClient, logger *logger.Logger) *L2GasEstimator {
	return &L2GasEstimator{
		client:             client,
		logger:             logger,
		baseFeeMultiplier:  1.1,                    // 10% buffer on base fee
		priorityFeeMin:     big.NewInt(100000000),  // 0.1 gwei minimum
		priorityFeeMax:     big.NewInt(2000000000), // 2 gwei maximum
		gasLimitMultiplier: 1.2,                    // 20% buffer on gas limit
	}
}

// EstimateL2Gas provides comprehensive gas estimation for L2 transactions
func (g *L2GasEstimator) EstimateL2Gas(ctx context.Context, tx *types.Transaction) (*GasEstimate, error) {
	// Get current gas price data
	gasPrice, err := g.client.SuggestGasPrice(ctx)
	if err != nil {
		return nil, fmt.Errorf("failed to get gas price: %v", err)
	}

	// Estimate gas limit
	gasLimit, err := g.estimateGasLimit(ctx, tx)
	if err != nil {
		return nil, fmt.Errorf("failed to estimate gas limit: %v", err)
	}

	// Get L1 data fee (Arbitrum-specific)
	l1DataFee, err := g.estimateL1DataFee(ctx, tx)
	if err != nil {
		g.logger.Warn(fmt.Sprintf("Failed to estimate L1 data fee: %v", err))
		l1DataFee = big.NewInt(0)
	}

	// Calculate L2 compute fee
	gasLimitBigInt := new(big.Int).SetUint64(gasLimit)
	l2ComputeFee := new(big.Int).Mul(gasPrice, gasLimitBigInt)

	// Calculate priority fee
	priorityFee := g.calculateOptimalPriorityFee(ctx, gasPrice)

	// Calculate max fee per gas
	maxFeePerGas := new(big.Int).Add(gasPrice, priorityFee)

	// Total fee includes both L1 and L2 components
	totalFee := new(big.Int).Add(l1DataFee, l2ComputeFee)

	// Apply gas limit buffer
	bufferedGasLimit := uint64(float64(gasLimit) * g.gasLimitMultiplier)

	estimate := &GasEstimate{
		GasLimit:       bufferedGasLimit,
		MaxFeePerGas:   maxFeePerGas,
		MaxPriorityFee: priorityFee,
		L1DataFee:      l1DataFee,
		L2ComputeFee:   l2ComputeFee,
		TotalFee:       totalFee,
		Confidence:     g.calculateConfidence(gasPrice, priorityFee),
	}

	return estimate, nil
}

// estimateGasLimit estimates the gas limit for an L2 transaction
func (g *L2GasEstimator) estimateGasLimit(ctx context.Context, tx *types.Transaction) (uint64, error) {
	// Create a call message for gas estimation
	msg := ethereum.CallMsg{
		From:     common.Address{}, // Will be overridden
		To:       tx.To(),
		Value:    tx.Value(),
		Data:     tx.Data(),
		GasPrice: tx.GasPrice(),
	}

	// Estimate gas using the client
	gasLimit, err := g.client.EstimateGas(ctx, msg)
	if err != nil {
		// Fallback to default gas limits based on transaction type
		return g.getDefaultGasLimit(tx), nil
	}

	return gasLimit, nil
}

// estimateL1DataFee calculates the L1 data fee component (Arbitrum-specific)
func (g *L2GasEstimator) estimateL1DataFee(ctx context.Context, tx *types.Transaction) (*big.Int, error) {
	// Get current L1 gas price from Arbitrum's ArbGasInfo precompile
	_, err := g.getL1GasPrice(ctx)
	if err != nil {
		g.logger.Debug(fmt.Sprintf("Failed to get L1 gas price, using fallback: %v", err))
		// Fallback to estimated L1 gas price with historical average
		_ = g.getEstimatedL1GasPrice(ctx)
	}

	// Get L1 data fee multiplier from ArbGasInfo
	l1PricePerUnit, err := g.getL1PricePerUnit(ctx)
	if err != nil {
		g.logger.Debug(fmt.Sprintf("Failed to get L1 price per unit, using default: %v", err))
		l1PricePerUnit = big.NewInt(1000000000) // 1 gwei default
	}

	// Serialize the transaction to get the exact L1 calldata
	txData, err := g.serializeTransactionForL1(tx)
	if err != nil {
		return nil, fmt.Errorf("failed to serialize transaction: %w", err)
	}

	// Count zero and non-zero bytes (EIP-2028 pricing)
	zeroBytes := 0
	nonZeroBytes := 0

	for _, b := range txData {
		if b == 0 {
			zeroBytes++
		} else {
			nonZeroBytes++
		}
	}

	// Calculate L1 gas used based on EIP-2028 formula
	// 4 gas per zero byte, 16 gas per non-zero byte
	l1GasUsed := int64(zeroBytes*4 + nonZeroBytes*16)

	// Add base transaction overhead (21000 gas)
	l1GasUsed += 21000

	// Add signature verification cost (additional cost for ECDSA signature)
	l1GasUsed += 2000

	// Apply Arbitrum's L1 data fee calculation
	// L1 data fee = l1GasUsed * l1PricePerUnit * baseFeeScalar
	baseFeeScalar, err := g.getBaseFeeScalar(ctx)
	if err != nil {
		g.logger.Debug(fmt.Sprintf("Failed to get base fee scalar, using default: %v", err))
		baseFeeScalar = big.NewInt(1300000) // Default scalar of 1.3
	}

	// Calculate the L1 data fee
	l1GasCost := new(big.Int).Mul(big.NewInt(l1GasUsed), l1PricePerUnit)
	l1DataFee := new(big.Int).Mul(l1GasCost, baseFeeScalar)
	l1DataFee = new(big.Int).Div(l1DataFee, big.NewInt(1000000)) // Scale down by 10^6

	g.logger.Debug(fmt.Sprintf("L1 data fee calculation: gasUsed=%d, pricePerUnit=%s, scalar=%s, fee=%s",
		l1GasUsed, l1PricePerUnit.String(), baseFeeScalar.String(), l1DataFee.String()))

	return l1DataFee, nil
}

// calculateOptimalPriorityFee calculates an optimal priority fee for fast inclusion
func (g *L2GasEstimator) calculateOptimalPriorityFee(ctx context.Context, baseFee *big.Int) *big.Int {
	// Try to get recent priority fees from the network
	priorityFee, err := g.getSuggestedPriorityFee(ctx)
	if err != nil {
		// Fallback to base fee percentage
		priorityFee = new(big.Int).Div(baseFee, big.NewInt(10)) // 10% of base fee
	}

	// Ensure within bounds
	if priorityFee.Cmp(g.priorityFeeMin) < 0 {
		priorityFee = new(big.Int).Set(g.priorityFeeMin)
	}
	if priorityFee.Cmp(g.priorityFeeMax) > 0 {
		priorityFee = new(big.Int).Set(g.priorityFeeMax)
	}

	return priorityFee
}

// getSuggestedPriorityFee gets suggested priority fee from the network
func (g *L2GasEstimator) getSuggestedPriorityFee(ctx context.Context) (*big.Int, error) {
	// Use eth_maxPriorityFeePerGas if available
	var result string
	err := g.client.rpcClient.CallContext(ctx, &result, "eth_maxPriorityFeePerGas")
	if err != nil {
		return nil, err
	}

	priorityFee := new(big.Int)
	if _, success := priorityFee.SetString(result[2:], 16); !success {
		return nil, fmt.Errorf("invalid priority fee response")
	}

	return priorityFee, nil
}

// calculateConfidence calculates confidence level for the gas estimate
func (g *L2GasEstimator) calculateConfidence(gasPrice, priorityFee *big.Int) float64 {
	// Higher priority fee relative to gas price = higher confidence
	ratio := new(big.Float).Quo(new(big.Float).SetInt(priorityFee), new(big.Float).SetInt(gasPrice))
	ratioFloat, _ := ratio.Float64()

	// Confidence scale: 0.1 ratio = 0.5 confidence, 0.5 ratio = 0.9 confidence
	confidence := 0.3 + (ratioFloat * 1.2)
	if confidence > 1.0 {
		confidence = 1.0
	}
	if confidence < 0.1 {
		confidence = 0.1
	}

	return confidence
}

// getDefaultGasLimit returns default gas limits based on transaction type
func (g *L2GasEstimator) getDefaultGasLimit(tx *types.Transaction) uint64 {
	dataSize := len(tx.Data())

	switch {
	case dataSize == 0:
		// Simple transfer
		return 21000
	case dataSize < 100:
		// Simple contract interaction
		return 50000
	case dataSize < 1000:
		// Complex contract interaction
		return 150000
	case dataSize < 5000:
		// Very complex interaction (e.g., DEX swap)
		return 300000
	default:
		// Extremely complex interaction
		return 500000
	}
}

// OptimizeForSpeed adjusts gas parameters for fastest execution
func (g *L2GasEstimator) OptimizeForSpeed(estimate *GasEstimate) *GasEstimate {
	optimized := *estimate

	// Increase priority fee by 50%
	speedPriorityFee := new(big.Int).Mul(estimate.MaxPriorityFee, big.NewInt(150))
	optimized.MaxPriorityFee = new(big.Int).Div(speedPriorityFee, big.NewInt(100))

	// Increase max fee per gas accordingly
	optimized.MaxFeePerGas = new(big.Int).Add(
		new(big.Int).Sub(estimate.MaxFeePerGas, estimate.MaxPriorityFee),
		optimized.MaxPriorityFee,
	)

	// Increase gas limit by 10% more
	optimized.GasLimit = uint64(float64(estimate.GasLimit) * 1.1)

	// Recalculate total fee
	gasLimitBigInt := new(big.Int).SetUint64(optimized.GasLimit)
	l2Fee := new(big.Int).Mul(optimized.MaxFeePerGas, gasLimitBigInt)
	optimized.TotalFee = new(big.Int).Add(estimate.L1DataFee, l2Fee)

	// Higher confidence due to aggressive pricing
	optimized.Confidence = estimate.Confidence * 1.2
	if optimized.Confidence > 1.0 {
		optimized.Confidence = 1.0
	}

	return &optimized
}

// OptimizeForCost adjusts gas parameters for lowest cost
func (g *L2GasEstimator) OptimizeForCost(estimate *GasEstimate) *GasEstimate {
	optimized := *estimate

	// Use minimum priority fee
	optimized.MaxPriorityFee = new(big.Int).Set(g.priorityFeeMin)

	// Reduce max fee per gas
	optimized.MaxFeePerGas = new(big.Int).Add(
		new(big.Int).Sub(estimate.MaxFeePerGas, estimate.MaxPriorityFee),
		optimized.MaxPriorityFee,
	)

	// Use exact gas limit (no buffer)
	optimized.GasLimit = uint64(float64(estimate.GasLimit) / g.gasLimitMultiplier)

	// Recalculate total fee
	gasLimitBigInt := new(big.Int).SetUint64(optimized.GasLimit)
	l2Fee := new(big.Int).Mul(optimized.MaxFeePerGas, gasLimitBigInt)
	optimized.TotalFee = new(big.Int).Add(estimate.L1DataFee, l2Fee)

	// Lower confidence due to minimal gas pricing
	optimized.Confidence = estimate.Confidence * 0.7

	return &optimized
}

// IsL2TransactionViable checks if an L2 transaction is economically viable
func (g *L2GasEstimator) IsL2TransactionViable(estimate *GasEstimate, expectedProfit *big.Int) bool {
	// Compare total fee to expected profit
	return estimate.TotalFee.Cmp(expectedProfit) < 0
}

// getL1GasPrice fetches the current L1 gas price from Arbitrum's ArbGasInfo precompile
func (g *L2GasEstimator) getL1GasPrice(ctx context.Context) (*big.Int, error) {
	// ArbGasInfo precompile address on Arbitrum
	arbGasInfoAddr := common.HexToAddress("0x000000000000000000000000000000000000006C")

	// Call getL1BaseFeeEstimate() function (function selector: 0xf5d6ded7)
	data := common.Hex2Bytes("f5d6ded7")

	msg := ethereum.CallMsg{
		To:   &arbGasInfoAddr,
		Data: data,
	}

	result, err := g.client.CallContract(ctx, msg, nil)
	if err != nil {
		return nil, fmt.Errorf("failed to call ArbGasInfo.getL1BaseFeeEstimate: %w", err)
	}

	if len(result) < 32 {
		return nil, fmt.Errorf("invalid response length from ArbGasInfo")
	}

	l1GasPrice := new(big.Int).SetBytes(result[:32])
	g.logger.Debug(fmt.Sprintf("Retrieved L1 gas price from ArbGasInfo: %s wei", l1GasPrice.String()))

	return l1GasPrice, nil
}

// getEstimatedL1GasPrice provides a fallback L1 gas price estimate using historical data
func (g *L2GasEstimator) getEstimatedL1GasPrice(ctx context.Context) *big.Int {
	// Try to get recent blocks to estimate average L1 gas price
	latestBlock, err := g.client.BlockByNumber(ctx, nil)
	if err != nil {
		g.logger.Debug(fmt.Sprintf("Failed to get latest block for gas estimation: %v", err))
		return big.NewInt(20000000000) // 20 gwei fallback
	}

	// Analyze last 10 blocks for gas price trend
	blockCount := int64(10)
	totalGasPrice := big.NewInt(0)
	validBlocks := int64(0)

	for i := int64(0); i < blockCount; i++ {
		blockNum := new(big.Int).Sub(latestBlock.Number(), big.NewInt(i))
		if blockNum.Sign() <= 0 {
			break
		}

		block, err := g.client.BlockByNumber(ctx, blockNum)
		if err != nil {
			continue
		}

		// Use base fee as proxy for gas price trend
		if block.BaseFee() != nil {
			totalGasPrice.Add(totalGasPrice, block.BaseFee())
			validBlocks++
		}
	}

	if validBlocks > 0 {
		avgGasPrice := new(big.Int).Div(totalGasPrice, big.NewInt(validBlocks))
		// Scale up for L1 (L1 typically 5-10x higher than L2)
		l1Estimate := new(big.Int).Mul(avgGasPrice, big.NewInt(7))

		g.logger.Debug(fmt.Sprintf("Estimated L1 gas price from %d blocks: %s wei", validBlocks, l1Estimate.String()))
		return l1Estimate
	}

	// Final fallback
	return big.NewInt(25000000000) // 25 gwei
}

// getL1PricePerUnit fetches the L1 price per unit from ArbGasInfo
func (g *L2GasEstimator) getL1PricePerUnit(ctx context.Context) (*big.Int, error) {
	// ArbGasInfo precompile address
	arbGasInfoAddr := common.HexToAddress("0x000000000000000000000000000000000000006C")

	// Call getPerBatchGasCharge() function (function selector: 0x6eca253a)
	data := common.Hex2Bytes("6eca253a")

	msg := ethereum.CallMsg{
		To:   &arbGasInfoAddr,
		Data: data,
	}

	result, err := g.client.CallContract(ctx, msg, nil)
	if err != nil {
		return nil, fmt.Errorf("failed to call ArbGasInfo.getPerBatchGasCharge: %w", err)
	}

	if len(result) < 32 {
		return nil, fmt.Errorf("invalid response length from ArbGasInfo")
	}

	pricePerUnit := new(big.Int).SetBytes(result[:32])
	g.logger.Debug(fmt.Sprintf("Retrieved L1 price per unit: %s", pricePerUnit.String()))

	return pricePerUnit, nil
}

// getBaseFeeScalar fetches the base fee scalar from ArbGasInfo
func (g *L2GasEstimator) getBaseFeeScalar(ctx context.Context) (*big.Int, error) {
	// ArbGasInfo precompile address
	arbGasInfoAddr := common.HexToAddress("0x000000000000000000000000000000000000006C")

	// Call getL1FeesAvailable() function (function selector: 0x5ca5a4d7) to get pricing info
	data := common.Hex2Bytes("5ca5a4d7")

	msg := ethereum.CallMsg{
		To:   &arbGasInfoAddr,
		Data: data,
	}

	result, err := g.client.CallContract(ctx, msg, nil)
	if err != nil {
		return nil, fmt.Errorf("failed to call ArbGasInfo.getL1FeesAvailable: %w", err)
	}

	if len(result) < 32 {
		return nil, fmt.Errorf("invalid response length from ArbGasInfo")
	}

	// Extract the scalar from the response (typically in the first 32 bytes)
	scalar := new(big.Int).SetBytes(result[:32])

	// Ensure scalar is reasonable (between 1.0 and 2.0, scaled by 10^6)
	minScalar := big.NewInt(1000000) // 1.0
	maxScalar := big.NewInt(2000000) // 2.0

	if scalar.Cmp(minScalar) < 0 {
		scalar = minScalar
	}
	if scalar.Cmp(maxScalar) > 0 {
		scalar = maxScalar
	}

	g.logger.Debug(fmt.Sprintf("Retrieved base fee scalar: %s", scalar.String()))
	return scalar, nil
}

// serializeTransactionForL1 serializes the transaction as it would appear on L1
func (g *L2GasEstimator) serializeTransactionForL1(tx *types.Transaction) ([]byte, error) {
	// For L1 data fee calculation, we need the transaction as it would be serialized on L1
	// This includes the complete transaction data including signature

	// Get the transaction data
	txData := tx.Data()

	// Create a basic serialization that includes:
	// - nonce (8 bytes)
	// - gas price (32 bytes)
	// - gas limit (8 bytes)
	// - to address (20 bytes)
	// - value (32 bytes)
	// - data (variable)
	// - v, r, s signature (65 bytes total)

	serialized := make([]byte, 0, 165+len(txData))

	// Add transaction fields (simplified encoding)
	nonce := tx.Nonce()
	nonceBigInt := new(big.Int).SetUint64(nonce)
	serialized = append(serialized, nonceBigInt.Bytes()...)

	if tx.GasPrice() != nil {
		gasPrice := tx.GasPrice().Bytes()
		serialized = append(serialized, gasPrice...)
	}

	gasLimit := tx.Gas()
	gasLimitBigInt := new(big.Int).SetUint64(gasLimit)
	serialized = append(serialized, gasLimitBigInt.Bytes()...)

	if tx.To() != nil {
		serialized = append(serialized, tx.To().Bytes()...)
	} else {
		// Contract creation - add 20 zero bytes
		serialized = append(serialized, make([]byte, 20)...)
	}

	if tx.Value() != nil {
		value := tx.Value().Bytes()
		serialized = append(serialized, value...)
	}

	// Add the transaction data
	serialized = append(serialized, txData...)

	// Add signature components (v, r, s) - 65 bytes total
	// For estimation purposes, we'll add placeholder signature bytes
	v, r, s := tx.RawSignatureValues()
	if v != nil && r != nil && s != nil {
		serialized = append(serialized, v.Bytes()...)
		serialized = append(serialized, r.Bytes()...)
		serialized = append(serialized, s.Bytes()...)
	} else {
		// Add placeholder signature (65 bytes)
		serialized = append(serialized, make([]byte, 65)...)
	}

	g.logger.Debug(fmt.Sprintf("Serialized transaction for L1 fee calculation: %d bytes", len(serialized)))
	return serialized, nil
}

// EstimateSwapGas implements math.GasEstimator interface
func (g *L2GasEstimator) EstimateSwapGas(exchange math.ExchangeType, poolData *math.PoolData) (uint64, error) {
	// Base gas for different exchange types on Arbitrum L2
	baseGas := map[math.ExchangeType]uint64{
		math.ExchangeUniswapV2: 120000, // Uniswap V2 swap
		math.ExchangeUniswapV3: 150000, // Uniswap V3 swap (more complex)
		math.ExchangeSushiSwap: 125000, // SushiSwap swap
		math.ExchangeCamelot:   140000, // Camelot swap
		math.ExchangeBalancer:  180000, // Balancer swap (complex)
		math.ExchangeCurve:     160000, // Curve swap
		math.ExchangeTraderJoe: 130000, // TraderJoe swap
		math.ExchangeRamses:    135000, // Ramses swap
	}

	gas, exists := baseGas[exchange]
	if !exists {
		gas = 150000 // Default fallback
	}

	// Apply L2 gas limit multiplier
	return uint64(float64(gas) * g.gasLimitMultiplier), nil
}

// EstimateFlashSwapGas implements math.GasEstimator interface
func (g *L2GasEstimator) EstimateFlashSwapGas(route []*math.PoolData) (uint64, error) {
	// Base flash swap overhead on Arbitrum L2
	baseGas := uint64(200000)

	// Add gas for each hop in the route
	hopGas := uint64(len(route)) * 50000

	// Add complexity gas based on different exchanges
	complexityGas := uint64(0)
	for _, pool := range route {
		switch pool.ExchangeType {
		case math.ExchangeUniswapV3:
			complexityGas += 30000 // V3 concentrated liquidity complexity
		case math.ExchangeBalancer:
			complexityGas += 50000 // Weighted pool complexity
		case math.ExchangeCurve:
			complexityGas += 40000 // Stable swap complexity
		case math.ExchangeTraderJoe:
			complexityGas += 25000 // TraderJoe complexity
		case math.ExchangeRamses:
			complexityGas += 35000 // Ramses complexity
		default:
			complexityGas += 20000 // Standard AMM
		}
	}

	totalGas := baseGas + hopGas + complexityGas

	// Apply L2 gas limit multiplier with safety margin for flash swaps
	return uint64(float64(totalGas) * g.gasLimitMultiplier * 1.5), nil
}

// GetCurrentGasPrice implements math.GasEstimator interface
func (g *L2GasEstimator) GetCurrentGasPrice() (*math.UniversalDecimal, error) {
	ctx := context.Background()

	// Get current gas price from the network
	gasPrice, err := g.client.Client.SuggestGasPrice(ctx)
	if err != nil {
		// Fallback to typical Arbitrum L2 gas price
		gasPrice = big.NewInt(100000000) // 0.1 gwei
		g.logger.Warn(fmt.Sprintf("Failed to get gas price, using fallback: %v", err))
	}

	// Apply base fee multiplier
	adjustedGasPrice := new(big.Int).Mul(gasPrice, big.NewInt(int64(g.baseFeeMultiplier*100)))
	adjustedGasPrice = new(big.Int).Div(adjustedGasPrice, big.NewInt(100))

	// Convert to UniversalDecimal (gas price is in wei, so 18 decimals)
	gasPriceDecimal, err := math.NewUniversalDecimal(adjustedGasPrice, 18, "GWEI")
	if err != nil {
		return nil, fmt.Errorf("failed to convert gas price to decimal: %w", err)
	}

	return gasPriceDecimal, nil
}