mev-beta/pkg/sequencer/decoder.go

package sequencer

import (
	"encoding/base64"
	"encoding/hex"
	"fmt"
	"math/big"

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

	"github.com/your-org/mev-bot/pkg/config"
	"github.com/your-org/mev-bot/pkg/validation"
)

// Package-level DEX configuration
var dexConfig *config.DEXConfig

// InitDEXConfig loads the DEX configuration from file
func InitDEXConfig(configPath string) error {
	cfg, err := config.LoadDEXConfig(configPath)
	if err != nil {
		return fmt.Errorf("failed to load DEX config: %w", err)
	}
	dexConfig = cfg
	return nil
}

// L2MessageKind represents the type of L2 message
type L2MessageKind uint8

const (
	L2MessageKind_SignedTx           L2MessageKind = 4
	L2MessageKind_Batch              L2MessageKind = 3
	L2MessageKind_SignedCompressedTx L2MessageKind = 7
)

// ArbitrumMessage represents a decoded Arbitrum sequencer message
type ArbitrumMessage struct {
	SequenceNumber uint64
	Kind           uint8
	BlockNumber    uint64
	Timestamp      uint64
	L2MsgRaw       string // Base64 encoded
	Transaction    *DecodedTransaction
}

// DecodedTransaction represents a decoded Arbitrum transaction
type DecodedTransaction struct {
	Hash     common.Hash
	From     common.Address
	To       *common.Address
	Value    *big.Int
	Data     []byte
	Nonce    uint64
	GasPrice *big.Int
	GasLimit uint64
	RawBytes []byte // RLP-encoded transaction bytes for reconstruction
}

// DecodeArbitrumMessage decodes an Arbitrum sequencer feed message
func DecodeArbitrumMessage(msgMap map[string]interface{}) (*ArbitrumMessage, error) {
	msg := &ArbitrumMessage{}

	// Extract sequence number
	if seqNum, ok := msgMap["sequenceNumber"].(float64); ok {
		msg.SequenceNumber = uint64(seqNum)
	}

	// Extract nested message structure
	messageWrapper, ok := msgMap["message"].(map[string]interface{})
	if !ok {
		return nil, fmt.Errorf("missing message wrapper")
	}

	message, ok := messageWrapper["message"].(map[string]interface{})
	if !ok {
		return nil, fmt.Errorf("missing inner message")
	}

	// Extract header
	if header, ok := message["header"].(map[string]interface{}); ok {
		if kind, ok := header["kind"].(float64); ok {
			msg.Kind = uint8(kind)
		}
		if blockNum, ok := header["blockNumber"].(float64); ok {
			msg.BlockNumber = uint64(blockNum)
		}
		if timestamp, ok := header["timestamp"].(float64); ok {
			msg.Timestamp = uint64(timestamp)
		}
	}

	// Extract l2Msg
	l2MsgBase64, ok := message["l2Msg"].(string)
	if !ok {
		return nil, fmt.Errorf("missing l2Msg")
	}
	msg.L2MsgRaw = l2MsgBase64

	// Decode transaction if it's a signed transaction (kind 3 from header means L1MessageType_L2Message)
	if msg.Kind == 3 {
		tx, err := DecodeL2Transaction(l2MsgBase64)
		if err != nil {
			// Not all messages are transactions, just skip
			return msg, nil
		}
		msg.Transaction = tx
	}

	return msg, nil
}

// DecodeL2Transaction decodes a base64-encoded L2 transaction
func DecodeL2Transaction(l2MsgBase64 string) (*DecodedTransaction, error) {
	// Step 1: Base64 decode
	decoded, err := base64.StdEncoding.DecodeString(l2MsgBase64)
	if err != nil {
		return nil, fmt.Errorf("base64 decode failed: %w", err)
	}

	if len(decoded) == 0 {
		return nil, fmt.Errorf("empty decoded message")
	}

	// Step 2: First byte is L2MessageKind
	l2Kind := L2MessageKind(decoded[0])

	// Only process signed transactions
	if l2Kind != L2MessageKind_SignedTx {
		return nil, fmt.Errorf("not a signed transaction (kind=%d)", l2Kind)
	}

	// Step 3: Strip first byte and RLP decode the transaction
	txBytes := decoded[1:]
	if len(txBytes) == 0 {
		return nil, fmt.Errorf("empty transaction bytes")
	}

	// Try to decode as Ethereum transaction
	tx := new(types.Transaction)
	if err := rlp.DecodeBytes(txBytes, tx); err != nil {
		return nil, fmt.Errorf("RLP decode failed: %w", err)
	}

	// Calculate transaction hash
	txHash := crypto.Keccak256Hash(txBytes)

	// Extract sender (requires chainID for EIP-155)
	// For now, we'll skip sender recovery as it requires the chain ID
	// and signature verification. We're mainly interested in To and Data.

	result := &DecodedTransaction{
		Hash:     txHash,
		To:       tx.To(),
		Value:    tx.Value(),
		Data:     tx.Data(),
		Nonce:    tx.Nonce(),
		GasPrice: tx.GasPrice(),
		GasLimit: tx.Gas(),
		RawBytes: txBytes, // Store for later reconstruction
	}

	return result, nil
}

// ToEthereumTransaction converts a DecodedTransaction back to *types.Transaction
// This is a reusable utility for converting our decoded format to go-ethereum format
func (dt *DecodedTransaction) ToEthereumTransaction() (*types.Transaction, error) {
	if len(dt.RawBytes) == 0 {
		return nil, fmt.Errorf("no raw transaction bytes available")
	}

	tx := new(types.Transaction)
	if err := rlp.DecodeBytes(dt.RawBytes, tx); err != nil {
		return nil, fmt.Errorf("failed to decode transaction: %w", err)
	}

	return tx, nil
}

// IsSwapTransaction checks if the transaction data is a DEX swap
func IsSwapTransaction(data []byte) bool {
	if len(data) < 4 {
		return false
	}

	// Extract function selector (first 4 bytes)
	selector := hex.EncodeToString(data[0:4])

	// Common DEX swap function selectors
	swapSelectors := map[string]string{
		// UniswapV2 Router
		"38ed1739": "swapExactTokensForTokens",
		"8803dbee": "swapTokensForExactTokens",
		"7ff36ab5": "swapExactETHForTokens",
		"fb3bdb41": "swapETHForExactTokens",
		"18cbafe5": "swapExactTokensForETH",
		"4a25d94a": "swapTokensForExactETH",

		// UniswapV3 Router
		"414bf389": "exactInputSingle",
		"c04b8d59": "exactInput",
		"db3e2198": "exactOutputSingle",
		"f28c0498": "exactOutput",

		// UniswapV2 Pair (direct swap)
		"022c0d9f": "swap",

		// Curve
		"3df02124": "exchange",
		"a6417ed6": "exchange_underlying",

		// 1inch
		"7c025200": "swap",
		"e449022e": "uniswapV3Swap",

		// 0x Protocol
		"d9627aa4": "sellToUniswap",
		"415565b0": "fillRfqOrder",
	}

	_, isSwap := swapSelectors[selector]
	return isSwap
}

// DEXProtocol represents a DEX protocol
type DEXProtocol struct {
	Name    string
	Version string
	Type    string // "router" or "pool"
}

// GetSwapProtocol identifies the DEX protocol from transaction data
func GetSwapProtocol(to *common.Address, data []byte) *DEXProtocol {
	if to == nil || len(data) < 4 {
		return &DEXProtocol{Name: "unknown", Version: "", Type: ""}
	}

	// Validate address is not zero
	if err := validation.ValidateAddressPtr(to); err != nil {
		return &DEXProtocol{Name: "unknown", Version: "", Type: ""}
	}

	selector := hex.EncodeToString(data[0:4])
	toAddr := to.Hex()

	// Check if it's a known router (from config if loaded, else use fallback)
	if dexConfig != nil {
		for addr, routerCfg := range dexConfig.Routers {
			if addr == toAddr {
				return &DEXProtocol{
					Name:    routerCfg.Name,
					Version: routerCfg.Version,
					Type:    routerCfg.Type,
				}
			}
		}
	}

	// Try to identify by function selector
	switch selector {
	// UniswapV2-style swap
	case "022c0d9f":
		return &DEXProtocol{Name: "UniswapV2", Version: "", Type: "pool"}

	// UniswapV2 Router
	case "38ed1739", "8803dbee", "7ff36ab5", "fb3bdb41", "18cbafe5", "4a25d94a":
		return &DEXProtocol{Name: "UniswapV2", Version: "", Type: "router"}

	// UniswapV3 Router
	case "414bf389", "c04b8d59", "db3e2198", "f28c0498", "5ae401dc", "ac9650d8":
		return &DEXProtocol{Name: "UniswapV3", Version: "", Type: "router"}

	// Curve
	case "3df02124", "a6417ed6", "394747c5", "5b41b908":
		return &DEXProtocol{Name: "Curve", Version: "", Type: "pool"}

	// Balancer
	case "52bbbe29": // swap
		return &DEXProtocol{Name: "Balancer", Version: "V2", Type: "vault"}

	// Camelot V3 swap
	case "128acb08": // exactInputSingle for Camelot V3
		return &DEXProtocol{Name: "Camelot", Version: "V3", Type: "router"}

	default:
		return &DEXProtocol{Name: "unknown", Version: "", Type: ""}
	}
}

// IsSupportedDEX checks if the protocol is one we want to track
func IsSupportedDEX(protocol *DEXProtocol) bool {
	if protocol == nil {
		return false
	}

	supportedDEXes := map[string]bool{
		"UniswapV2":       true,
		"UniswapV3":       true,
		"UniswapUniversal": true,
		"SushiSwap":       true,
		"Camelot":         true,
		"Balancer":        true,
		"Curve":           true,
		"KyberSwap":       true,
	}

	return supportedDEXes[protocol.Name]
}