mev-beta/pkg/arbitrum/abi_decoder.go

// Package arbitrum provides functionality for decoding and analyzing Arbitrum blockchain transactions,
// with a particular focus on DEX (Decentralized Exchange) transaction analysis and ABI decoding.
// This package is critical for the MEV bot's ability to identify arbitrage opportunities by
// understanding the structure and content of DEX transactions.
package arbitrum

import (
	"context"
	"encoding/hex"
	"fmt"
	"math/big"
	"strings"
	"time"

	"github.com/ethereum/go-ethereum"
	"github.com/ethereum/go-ethereum/accounts/abi"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/crypto"
	"github.com/ethereum/go-ethereum/ethclient"
)

// ABIDecoder handles proper ABI (Application Binary Interface) decoding for DEX transactions.
// This is a critical component of the MEV bot that enables it to understand and parse
// complex transaction data from various decentralized exchanges on Arbitrum.
//
// The decoder performs several key functions:
// 1. Decodes transaction input data to extract function calls and parameters
// 2. Validates contract types to prevent ERC-20/pool confusion (critical fix)
// 3. Supports multiple DEX protocols with their specific ABI patterns
// 4. Provides runtime contract validation using RPC calls
type ABIDecoder struct {
	// ABI definitions for major DEX protocols supported on Arbitrum
	// These are used for precise transaction decoding when available
	uniswapV2ABI abi.ABI // Uniswap V2 and compatible protocols (SushiSwap, etc.)
	uniswapV3ABI abi.ABI // Uniswap V3 and compatible protocols (Camelot V3, etc.)
	sushiswapABI abi.ABI // SushiSwap-specific functions
	camelotABI   abi.ABI // Camelot DEX on Arbitrum
	balancerABI  abi.ABI // Balancer V2 pools
	curveABI     abi.ABI // Curve Finance stable pools
	oneInchABI   abi.ABI // 1inch aggregator

	// Function signature mappings for fast lookup of transaction types
	// Maps 4-byte function selectors (e.g., "0x38ed1739") to human-readable signatures
	functionSignatures map[string]string

	// Contract type validation components (CRITICAL FIX IMPLEMENTATION)
	// These prevent the costly error where ERC-20 tokens are misclassified as pool contracts
	client           *ethclient.Client // RPC client for runtime contract validation
	enableValidation bool              // Flag to enable/disable validation (default: true for safety)
}

// SwapParams represents the decoded parameters from a DEX swap transaction.
// This structure contains all the essential information needed to analyze
// arbitrage opportunities and understand the economic impact of a trade.
type SwapParams struct {
	// Trade amounts and constraints
	AmountIn     *big.Int // Input amount being swapped (in token decimals)
	AmountOut    *big.Int // Expected output amount (in token decimals)
	MinAmountOut *big.Int // Minimum acceptable output (slippage protection)

	// Token and address information
	TokenIn   common.Address   // Address of the input token contract
	TokenOut  common.Address   // Address of the output token contract
	Recipient common.Address   // Address that will receive the output tokens
	Pool      common.Address   // Address of the liquidity pool being used
	Path      []common.Address // Multi-hop path for complex swaps (token0 -> token1 -> token2)

	// Transaction constraints and fees
	Deadline *big.Int // Unix timestamp after which the transaction is invalid
	Fee      *big.Int // Fee tier for Uniswap V3 pools (e.g., 500 = 0.05%)
}

// NewABIDecoder creates a new ABI decoder with support for all major Arbitrum DEX protocols.
// The decoder is initialized with comprehensive function signature mappings and validation enabled by default.
// This is the primary entry point for creating a decoder instance.
//
// Returns:
//   - *ABIDecoder: Configured decoder ready for transaction analysis
//   - error: Any initialization errors
func NewABIDecoder() (*ABIDecoder, error) {
	decoder := &ABIDecoder{
		// Initialize the function signature lookup table
		functionSignatures: make(map[string]string),
		// Enable validation by default to prevent contract type confusion
		enableValidation: true,
	}

	// Load all known DEX function signatures for fast transaction identification
	if err := decoder.initializeFunctionSignatures(); err != nil {
		return nil, fmt.Errorf("failed to initialize function signatures: %w", err)
	}

	return decoder, nil
}

// ValidateInputData performs enhanced input validation for ABI decoding (exported for testing)
func (d *ABIDecoder) ValidateInputData(data []byte, context string) error {
	// Enhanced bounds checking
	if data == nil {
		return fmt.Errorf("ABI decoding validation failed: input data is nil in context %s", context)
	}

	// Check minimum size requirements
	if len(data) < 4 {
		return fmt.Errorf("ABI decoding validation failed: insufficient data length %d (minimum 4 bytes) in context %s", len(data), context)
	}

	// Check maximum size to prevent DoS
	const maxDataSize = 1024 * 1024 // 1MB limit
	if len(data) > maxDataSize {
		return fmt.Errorf("ABI decoding validation failed: data size %d exceeds maximum %d in context %s", len(data), maxDataSize, context)
	}

	// Validate data alignment (ABI data should be 32-byte aligned after function selector)
	payloadSize := len(data) - 4 // Exclude function selector
	if payloadSize > 0 && payloadSize%32 != 0 {
		return fmt.Errorf("ABI decoding validation failed: payload size %d not 32-byte aligned in context %s", payloadSize, context)
	}

	return nil
}

// ValidateABIParameter performs enhanced ABI parameter validation (exported for testing)
func (d *ABIDecoder) ValidateABIParameter(data []byte, offset, size int, paramType string, context string) error {
	if offset < 0 {
		return fmt.Errorf("ABI parameter validation failed: negative offset %d for %s in context %s", offset, paramType, context)
	}

	if offset+size > len(data) {
		return fmt.Errorf("ABI parameter validation failed: parameter bounds [%d:%d] exceed data length %d for %s in context %s",
			offset, offset+size, len(data), paramType, context)
	}

	if size <= 0 {
		return fmt.Errorf("ABI parameter validation failed: invalid parameter size %d for %s in context %s", size, paramType, context)
	}

	// Specific validation for address parameters
	if paramType == "address" && size == 32 {
		// Check that first 12 bytes are zero for address type
		for i := 0; i < 12; i++ {
			if data[offset+i] != 0 {
				return fmt.Errorf("ABI parameter validation failed: invalid address padding for %s in context %s", paramType, context)
			}
		}
	}

	return nil
}

// ValidateArrayBounds performs enhanced array bounds validation (exported for testing)
func (d *ABIDecoder) ValidateArrayBounds(data []byte, arrayOffset, arrayLength uint64, elementSize int, context string) error {
	if arrayOffset >= uint64(len(data)) {
		return fmt.Errorf("ABI array validation failed: array offset %d exceeds data length %d in context %s", arrayOffset, len(data), context)
	}

	// Reasonable array length limits
	const maxArrayLength = 10000
	if arrayLength > maxArrayLength {
		return fmt.Errorf("ABI array validation failed: array length %d exceeds maximum %d in context %s", arrayLength, maxArrayLength, context)
	}

	// Check total array size doesn't exceed bounds
	totalArraySize := arrayLength * uint64(elementSize)
	if arrayOffset+32+totalArraySize > uint64(len(data)) {
		return fmt.Errorf("ABI array validation failed: array bounds [%d:%d] exceed data length %d in context %s",
			arrayOffset, arrayOffset+32+totalArraySize, len(data), context)
	}

	return nil
}

// WithClient enables runtime contract validation by providing an RPC client.
// When a client is provided, the decoder can perform on-chain contract calls
// to verify contract types and prevent ERC-20/pool confusion errors.
//
// This is essential for production use to avoid the costly misclassification
// that was causing 535K+ log messages and transaction failures.
//
// Parameters:
//   - client: Ethereum RPC client for contract validation
//
// Returns:
//   - *ABIDecoder: The decoder instance for method chaining
func (d *ABIDecoder) WithClient(client *ethclient.Client) *ABIDecoder {
	d.client = client
	return d
}

// WithValidation controls whether contract type validation is performed during decoding.
// Validation is highly recommended for production use to prevent costly errors.
//
// When validation is enabled:
//   - Contracts are verified to match their expected types
//   - ERC-20 tokens are prevented from being used as pool contracts
//   - Runtime checks are performed using RPC calls
//
// Parameters:
//   - enabled: true to enable validation (recommended), false to disable
//
// Returns:
//   - *ABIDecoder: The decoder instance for method chaining
func (d *ABIDecoder) WithValidation(enabled bool) *ABIDecoder {
	d.enableValidation = enabled
	return d
}

// initializeFunctionSignatures sets up known DEX function signatures
func (d *ABIDecoder) initializeFunctionSignatures() error {
	// Uniswap V2 signatures
	d.functionSignatures["0x38ed1739"] = "swapExactTokensForTokens(uint256,uint256,address[],address,uint256)"
	d.functionSignatures["0x8803dbee"] = "swapTokensForExactTokens(uint256,uint256,address[],address,uint256)"
	d.functionSignatures["0x7ff36ab5"] = "swapExactETHForTokens(uint256,address[],address,uint256)"
	d.functionSignatures["0x4a25d94a"] = "swapTokensForExactETH(uint256,uint256,address[],address,uint256)"
	d.functionSignatures["0x18cbafe5"] = "swapExactTokensForETH(uint256,uint256,address[],address,uint256)"
	d.functionSignatures["0xfb3bdb41"] = "swapETHForExactTokens(uint256,address[],address,uint256)"

	// Uniswap V3 signatures
	d.functionSignatures["0x414bf389"] = "exactInputSingle((address,address,uint24,address,uint256,uint256,uint256,uint160))"
	d.functionSignatures["0xc04b8d59"] = "exactInput((bytes,address,uint256,uint256,uint256))"
	d.functionSignatures["0xdb3e2198"] = "exactOutputSingle((address,address,uint24,address,uint256,uint256,uint256,uint160))"
	d.functionSignatures["0xf28c0498"] = "exactOutput((bytes,address,uint256,uint256,uint256))"

	// SushiSwap (same as Uniswap V2)
	// Camelot V3 (same as Uniswap V3)

	// 1inch aggregator signatures
	d.functionSignatures["0x7c025200"] = "swap(address,(address,address,address,address,uint256,uint256,uint256),bytes,bytes)"
	d.functionSignatures["0xe449022e"] = "uniswapV3Swap(uint256,uint256,uint256[])"

	// Balancer V2 signatures
	d.functionSignatures["0x52bbbe29"] = "swap((bytes32,uint8,address,address,uint256,bytes),(address,bool,address,bool),uint256,uint256)"

	// Radiant (lending protocol with swap functionality)
	d.functionSignatures["0xa9059cbb"] = "transfer(address,uint256)"                      // ERC-20 transfer
	d.functionSignatures["0x23b872dd"] = "transferFrom(address,address,uint256)"          // ERC-20 transferFrom
	d.functionSignatures["0xe8e33700"] = "deposit(address,uint256,address,uint16)"        // Aave-style deposit
	d.functionSignatures["0x69328dec"] = "withdraw(address,uint256,address)"              // Aave-style withdraw
	d.functionSignatures["0xa415bcad"] = "borrow(address,uint256,uint256,uint16,address)" // Aave-style borrow
	d.functionSignatures["0x563dd613"] = "repay(address,uint256,uint256,address)"         // Aave-style repay

	// Curve Finance signatures
	d.functionSignatures["0x3df02124"] = "exchange(int128,int128,uint256,uint256)"            // Curve exchange
	d.functionSignatures["0xa6417ed6"] = "exchange_underlying(int128,int128,uint256,uint256)" // Curve exchange underlying

	// Trader Joe (Arbitrum DEX)
	d.functionSignatures["0x18cbafe5"] = "swapExactTokensForTokens(uint256,uint256,address[],address,uint256)" // Same as Uniswap V2
	d.functionSignatures["0x791ac947"] = "swapExactTokensForTokensSupportingFeeOnTransferTokens(uint256,uint256,address[],address,uint256)"

	// GMX (perpetual trading)
	d.functionSignatures["0x0809dd62"] = "swap(address[],uint256,uint256,address)"                                  // GMX swap
	d.functionSignatures["0x29a5408c"] = "increasePosition(address[],address,uint256,uint256,uint256,bool,uint256)" // GMX position

	// Arbitrum-specific multicall patterns
	d.functionSignatures["0xac9650d8"] = "multicall(bytes[])"         // Common multicall
	d.functionSignatures["0x1f0464d1"] = "multicall(bytes[])"         // Alternative multicall
	d.functionSignatures["0x5ae401dc"] = "multicall(uint256,bytes[])" // Multicall with deadline

	// Universal Router signatures (critical for Arbitrum)
	d.functionSignatures["0x24856bc3"] = "execute(bytes,bytes[])"         // Universal Router execute
	d.functionSignatures["0x3593564c"] = "execute(bytes,bytes[],uint256)" // Universal Router execute with deadline
	d.functionSignatures["0x0000000c"] = "V3_SWAP_EXACT_IN"               // Universal Router command
	d.functionSignatures["0x0000000d"] = "V3_SWAP_EXACT_OUT"              // Universal Router command
	d.functionSignatures["0x00000008"] = "V2_SWAP_EXACT_IN"               // Universal Router V2 command
	d.functionSignatures["0x00000009"] = "V2_SWAP_EXACT_OUT"              // Universal Router V2 command

	// Additional Arbitrum DEX signatures
	d.functionSignatures["0x128acb08"] = "initialize(uint160)"                          // Uniswap V3 pool initialize
	d.functionSignatures["0x883164f6"] = "mint(address,int24,int24,uint128,bytes)"      // Uniswap V3 mint
	d.functionSignatures["0x128acb09"] = "collect(address,int24,int24,uint128,uint128)" // Uniswap V3 collect

	// Camelot DEX (Arbitrum-specific)
	d.functionSignatures["0x022c0d9f"] = "swap(uint256,uint256,address,bytes)" // Camelot swap
	d.functionSignatures["0x4515cef3"] = "deposit(address,uint256)"            // Camelot deposit

	// Radiant Capital (Arbitrum lending with swaps)
	d.functionSignatures["0x7535d246"] = "mint(uint256)"        // Radiant mint
	d.functionSignatures["0x852a12e3"] = "repayBorrow(uint256)" // Radiant repay

	return nil
}

// DecodeSwapTransaction decodes a swap transaction based on protocol and function signature
func (d *ABIDecoder) DecodeSwapTransaction(protocol, txData string) (*SwapParams, error) {
	if len(txData) < 10 { // 0x + 4 bytes function selector
		return nil, fmt.Errorf("transaction data too short")
	}

	// Remove 0x prefix if present
	if strings.HasPrefix(txData, "0x") {
		txData = txData[2:]
	}

	data, err := hex.DecodeString(txData)
	if err != nil {
		return nil, fmt.Errorf("failed to decode hex data: %w", err)
	}

	if len(data) < 4 {
		return nil, fmt.Errorf("insufficient data for function selector")
	}

	// Extract function selector
	selector := "0x" + hex.EncodeToString(data[:4])

	// Get function signature
	functionSig, exists := d.functionSignatures[selector]
	if !exists {
		// Try to decode as generic swap if signature unknown
		return d.decodeGenericSwap(data, protocol)
	}

	// Handle multicall transactions first
	if strings.Contains(functionSig, "multicall") {
		return d.decodeMulticall(data, protocol)
	}

	// Decode based on protocol and function
	switch protocol {
	case "uniswap_v2", "sushiswap", "camelot_v2", "trader_joe":
		return d.decodeUniswapV2Swap(data, functionSig)
	case "uniswap_v3", "camelot_v3", "algebra":
		return d.decodeUniswapV3Swap(data, functionSig)
	case "1inch":
		return d.decode1inchSwap(data, functionSig)
	case "balancer_v2":
		return d.decodeBalancerSwap(data, functionSig)
	case "curve":
		return d.decodeCurveSwap(data, functionSig)
	case "radiant", "aave", "compound":
		return d.decodeLendingSwap(data, functionSig)
	case "gmx":
		return d.decodeGMXSwap(data, functionSig)
	default:
		return d.decodeGenericSwap(data, protocol)
	}
}

// decodeUniswapV2Swap decodes Uniswap V2 style swap transactions
func (d *ABIDecoder) decodeUniswapV2Swap(data []byte, functionSig string) (*SwapParams, error) {
	if len(data) < 4 {
		return nil, fmt.Errorf("insufficient data")
	}

	params := &SwapParams{}

	// Skip function selector (first 4 bytes)
	data = data[4:]

	// Parse based on function type
	if strings.Contains(functionSig, "swapExactTokensForTokens") {
		if len(data) < 160 { // 5 * 32 bytes minimum
			return nil, fmt.Errorf("insufficient data for swapExactTokensForTokens")
		}

		// amountIn (32 bytes)
		params.AmountIn = new(big.Int).SetBytes(data[0:32])

		// amountOutMin (32 bytes)
		params.MinAmountOut = new(big.Int).SetBytes(data[32:64])

		// path offset (32 bytes) - skip this, get actual path
		pathOffset := new(big.Int).SetBytes(data[64:96]).Uint64()

		// recipient (32 bytes, but address is last 20 bytes)
		params.Recipient = common.BytesToAddress(data[96:128])

		// deadline (32 bytes)
		params.Deadline = new(big.Int).SetBytes(data[128:160])

		// Parse path array
		if pathOffset < uint64(len(data)) && pathOffset+32 < uint64(len(data)) {
			pathLength := new(big.Int).SetBytes(data[pathOffset : pathOffset+32]).Uint64()
			if pathLength >= 2 && pathOffset+32+pathLength*32 <= uint64(len(data)) {
				params.Path = make([]common.Address, pathLength)
				for i := uint64(0); i < pathLength; i++ {
					start := pathOffset + 32 + i*32
					params.Path[i] = common.BytesToAddress(data[start : start+32])
				}

				if len(params.Path) >= 2 {
					params.TokenIn = params.Path[0]
					params.TokenOut = params.Path[len(params.Path)-1]
				}
			}
		}
	}

	// Handle other Uniswap V2 functions similarly...

	return params, nil
}

// decodeUniswapV3Swap decodes Uniswap V3 style swap transactions
func (d *ABIDecoder) decodeUniswapV3Swap(data []byte, functionSig string) (*SwapParams, error) {
	if len(data) < 4 {
		return nil, fmt.Errorf("insufficient data")
	}

	params := &SwapParams{}
	data = data[4:] // Skip function selector

	if strings.Contains(functionSig, "exactInputSingle") {
		// ExactInputSingle struct: (tokenIn, tokenOut, fee, recipient, deadline, amountIn, amountOutMinimum, sqrtPriceLimitX96)
		if len(data) < 256 { // 8 * 32 bytes
			return nil, fmt.Errorf("insufficient data for exactInputSingle")
		}

		params.TokenIn = common.BytesToAddress(data[0:32])
		params.TokenOut = common.BytesToAddress(data[32:64])
		params.Fee = new(big.Int).SetBytes(data[64:96])
		params.Recipient = common.BytesToAddress(data[96:128])
		params.Deadline = new(big.Int).SetBytes(data[128:160])
		params.AmountIn = new(big.Int).SetBytes(data[160:192])
		params.MinAmountOut = new(big.Int).SetBytes(data[192:224])
		// sqrtPriceLimitX96 at data[224:256] - skip for now
	}

	// Handle other Uniswap V3 functions...

	return params, nil
}

// decode1inchSwap decodes 1inch aggregator swap transactions
func (d *ABIDecoder) decode1inchSwap(data []byte, functionSig string) (*SwapParams, error) {
	params := &SwapParams{}
	data = data[4:] // Skip function selector

	// 1inch has complex swap data, extract what we can
	if len(data) >= 64 {
		// First parameter is usually the caller/executor
		// Second parameter contains swap description with tokens and amounts
		if len(data) >= 160 {
			// Try to extract token addresses from swap description
			// This is a simplified extraction - 1inch has complex encoding
			params.TokenIn = common.BytesToAddress(data[32:64])
			params.TokenOut = common.BytesToAddress(data[64:96])
			params.AmountIn = new(big.Int).SetBytes(data[96:128])
			params.MinAmountOut = new(big.Int).SetBytes(data[128:160])
		}
	}

	return params, nil
}

// decodeBalancerSwap decodes Balancer V2 swap transactions
func (d *ABIDecoder) decodeBalancerSwap(data []byte, functionSig string) (*SwapParams, error) {
	params := &SwapParams{}
	data = data[4:] // Skip function selector

	// Balancer has complex swap structure with pool ID, tokens, amounts
	if len(data) >= 128 {
		// Extract basic information - Balancer encoding is complex
		// This is a simplified version
		params.AmountIn = new(big.Int).SetBytes(data[64:96])
		params.MinAmountOut = new(big.Int).SetBytes(data[96:128])
	}

	return params, nil
}

// decodeGenericSwap provides fallback decoding for unknown protocols with enhanced validation
func (d *ABIDecoder) decodeGenericSwap(data []byte, protocol string) (*SwapParams, error) {
	params := &SwapParams{}

	// Enhanced input validation
	if err := d.ValidateInputData(data, fmt.Sprintf("decodeGenericSwap-%s", protocol)); err != nil {
		return nil, err
	}

	data = data[4:] // Skip function selector

	// Enhanced bounds checking for payload
	if err := d.ValidateABIParameter(data, 0, len(data), "payload", fmt.Sprintf("decodeGenericSwap-%s-payload", protocol)); err != nil {
		return nil, err
	}

	// Try to extract common ERC-20 swap patterns
	if len(data) >= 128 { // Minimum for token addresses and amounts
		// Try different common patterns for token addresses

		// Pattern 1: Direct address parameters at start with validation
		if len(data) >= 64 {
			if err := d.ValidateABIParameter(data, 0, 32, "address", fmt.Sprintf("pattern1-tokenIn-%s", protocol)); err != nil {
				return nil, err
			}
			if err := d.ValidateABIParameter(data, 32, 32, "address", fmt.Sprintf("pattern1-tokenOut-%s", protocol)); err != nil {
				return nil, err
			}

			tokenIn := common.BytesToAddress(data[0:32])
			tokenOut := common.BytesToAddress(data[32:64])

			// Check if these look like valid token addresses (not zero)
			if d.isValidTokenAddress(tokenIn) && d.isValidTokenAddress(tokenOut) {
				params.TokenIn = tokenIn
				params.TokenOut = tokenOut
			}
		}

		// Pattern 2: Try offset-based token extraction with enhanced bounds checking
		if params.TokenIn == (common.Address{}) && len(data) >= 96 {
			// Sometimes tokens are at different offsets - validate each access
			for offset := 0; offset < 128 && offset+32 <= len(data); offset += 32 {
				if err := d.ValidateABIParameter(data, offset, 32, "address", fmt.Sprintf("pattern2-offset%d-%s", offset, protocol)); err != nil {
					continue // Skip invalid offsets
				}

				addr := common.BytesToAddress(data[offset : offset+32])
				if d.isValidTokenAddress(addr) {
					if params.TokenIn == (common.Address{}) {
						params.TokenIn = addr
					} else if params.TokenOut == (common.Address{}) && addr != params.TokenIn {
						params.TokenOut = addr
						break
					}
				}
			}
		}

		// Pattern 3: Look for array patterns with comprehensive validation
		if params.TokenIn == (common.Address{}) && len(data) >= 160 {
			// Look for dynamic arrays which often contain token paths
			for offset := 32; offset+64 <= len(data); offset += 32 {
				if err := d.ValidateABIParameter(data, offset, 32, "uint256", fmt.Sprintf("pattern3-offset%d-%s", offset, protocol)); err != nil {
					continue
				}

				// Check if this looks like an array offset
				possibleOffset := new(big.Int).SetBytes(data[offset : offset+32]).Uint64()
				if possibleOffset > 32 && possibleOffset < uint64(len(data)-64) {
					// Validate array header access
					if err := d.ValidateABIParameter(data, int(possibleOffset), 32, "array-length", fmt.Sprintf("pattern3-arraylen-%s", protocol)); err != nil {
						continue
					}

					// Check if there's an array length at this offset
					arrayLen := new(big.Int).SetBytes(data[possibleOffset : possibleOffset+32]).Uint64()

					// Enhanced array validation
					if err := d.ValidateArrayBounds(data, possibleOffset, arrayLen, 32, fmt.Sprintf("pattern3-array-%s", protocol)); err != nil {
						continue
					}

					if arrayLen >= 2 && arrayLen <= 10 {
						// Validate array element access before extraction
						if err := d.ValidateABIParameter(data, int(possibleOffset+32), 32, "address", fmt.Sprintf("pattern3-first-%s", protocol)); err != nil {
							continue
						}
						lastElementOffset := int(possibleOffset + 32 + (arrayLen-1)*32)
						if err := d.ValidateABIParameter(data, lastElementOffset, 32, "address", fmt.Sprintf("pattern3-last-%s", protocol)); err != nil {
							continue
						}

						// Extract first and last elements as token addresses
						firstToken := common.BytesToAddress(data[possibleOffset+32 : possibleOffset+64])
						lastToken := common.BytesToAddress(data[lastElementOffset : lastElementOffset+32])

						if d.isValidTokenAddress(firstToken) && d.isValidTokenAddress(lastToken) {
							params.TokenIn = firstToken
							params.TokenOut = lastToken
							break
						}
					}
				}
			}
		}

		// Extract amounts from common positions
		if len(data) >= 64 {
			// Try first amount
			params.AmountIn = new(big.Int).SetBytes(data[0:32])
			if params.AmountIn.Cmp(big.NewInt(0)) == 0 && len(data) >= 96 {
				params.AmountIn = new(big.Int).SetBytes(data[32:64])
			}
			if params.AmountIn.Cmp(big.NewInt(0)) == 0 && len(data) >= 128 {
				params.AmountIn = new(big.Int).SetBytes(data[64:96])
			}

			// Try to find amount out (usually after amount in)
			if len(data) >= 96 && params.AmountIn.Cmp(big.NewInt(0)) > 0 {
				params.MinAmountOut = new(big.Int).SetBytes(data[64:96])
				if params.MinAmountOut.Cmp(big.NewInt(0)) == 0 && len(data) >= 128 {
					params.MinAmountOut = new(big.Int).SetBytes(data[96:128])
				}
			}
		}

		// Try to find recipient address (often near the end)
		if len(data) >= 160 {
			// Check last few 32-byte slots for address patterns
			for i := len(data) - 32; i >= len(data)-96 && i >= 0; i -= 32 {
				addr := common.BytesToAddress(data[i : i+32])
				if d.isValidTokenAddress(addr) {
					params.Recipient = addr
					break
				}
			}
		}
	}

	// CRITICAL FIX: Validate extracted token addresses before returning
	if params.TokenIn == (common.Address{}) || params.TokenOut == (common.Address{}) {
		return nil, fmt.Errorf("failed to extract valid token addresses from transaction data for protocol %s", protocol)
	}

	if params.TokenIn == params.TokenOut {
		return nil, fmt.Errorf("tokenIn and tokenOut cannot be the same: %s", params.TokenIn.Hex())
	}

	// CRITICAL: Validate contract types to prevent ERC-20/pool confusion
	if d.enableValidation {
		if err := d.validateContractTypes(params); err != nil {
			return nil, fmt.Errorf("contract type validation failed: %w", err)
		}
	}

	return params, nil
}

// isValidTokenAddress checks if an address looks like a valid token address
func (d *ABIDecoder) isValidTokenAddress(addr common.Address) bool {
	// Check if not zero address
	if addr == (common.Address{}) {
		return false
	}

	// Check if not a common non-token address
	// Exclude known router/factory addresses that aren't tokens
	knownContracts := []common.Address{
		common.HexToAddress("0x4752ba5dbc23f44d87826276bf6fd6b1c372ad24"), // Uniswap V2 Router
		common.HexToAddress("0xE592427A0AEce92De3Edee1F18E0157C05861564"), // Uniswap V3 Router
		common.HexToAddress("0x68b3465833fb72A70ecDF485E0e4C7bD8665Fc45"), // Uniswap V3 Router02
		common.HexToAddress("0x1b02dA8Cb0d097eB8D57A175b88c7D8b47997506"), // SushiSwap Router
		common.HexToAddress("0x1F98431c8aD98523631AE4a59f267346ea31F984"), // Uniswap V3 Factory
		common.HexToAddress("0xc35DADB65012eC5796536bD9864eD8773aBc74C4"), // SushiSwap Factory
	}

	for _, contract := range knownContracts {
		if addr == contract {
			return false
		}
	}

	// Additional heuristics: valid token addresses typically have:
	// - Non-zero value
	// - Not ending in many zeros (contracts often do)
	// - Not matching common EOA patterns

	addrBytes := addr.Bytes()
	zeroCount := 0
	for i := len(addrBytes) - 4; i < len(addrBytes); i++ {
		if addrBytes[i] == 0 {
			zeroCount++
		}
	}

	// If last 4 bytes are all zeros, likely not a token
	if zeroCount >= 3 {
		return false
	}

	return true
}

// validateContractTypes validates that extracted addresses match expected contract types
func (d *ABIDecoder) validateContractTypes(params *SwapParams) error {
	if d.client == nil {
		return nil // Skip validation if no client available
	}

	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()

	// Validate TokenIn is actually an ERC-20 token
	if params.TokenIn != (common.Address{}) {
		if err := d.validateIsERC20Token(ctx, params.TokenIn); err != nil {
			return fmt.Errorf("TokenIn validation failed: %w", err)
		}
	}

	// Validate TokenOut is actually an ERC-20 token
	if params.TokenOut != (common.Address{}) {
		if err := d.validateIsERC20Token(ctx, params.TokenOut); err != nil {
			return fmt.Errorf("TokenOut validation failed: %w", err)
		}
	}

	// Validate Pool address if present (should be a pool, not a token)
	if params.Pool != (common.Address{}) {
		if err := d.validateIsPool(ctx, params.Pool); err != nil {
			return fmt.Errorf("Pool validation failed: %w", err)
		}

		// CRITICAL: Ensure pool address is not the same as token addresses
		if params.Pool == params.TokenIn {
			return fmt.Errorf("pool address cannot be the same as TokenIn: %s", params.Pool.Hex())
		}
		if params.Pool == params.TokenOut {
			return fmt.Errorf("pool address cannot be the same as TokenOut: %s", params.Pool.Hex())
		}
	}

	return nil
}

// validateIsERC20Token validates that an address is an ERC-20 token contract
func (d *ABIDecoder) validateIsERC20Token(ctx context.Context, address common.Address) error {
	// Test for basic ERC-20 functions
	erc20Functions := [][]byte{
		{0x70, 0xa0, 0x82, 0x31}, // balanceOf(address)
		{0x31, 0x3c, 0xe5, 0x67}, // decimals()
		{0x95, 0xd8, 0x9b, 0x41}, // symbol()
	}

	successCount := 0
	for _, funcSig := range erc20Functions {
		// Create a test call with zero address as parameter
		testData := make([]byte, 4+32)
		copy(testData[:4], funcSig)
		// Leave the rest as zeros (test parameter)

		_, err := d.client.CallContract(ctx, ethereum.CallMsg{
			To:   &address,
			Data: testData,
		}, nil)

		if err == nil {
			successCount++
		}
	}

	// Must support at least 2 out of 3 basic ERC-20 functions
	if successCount < 2 {
		return fmt.Errorf("address %s does not appear to be an ERC-20 token (supported %d/3 functions)", address.Hex(), successCount)
	}

	// CRITICAL: Ensure it's not a pool contract by testing pool-specific functions
	if d.appearsToBePool(ctx, address) {
		return fmt.Errorf("address %s appears to be a pool contract, not an ERC-20 token", address.Hex())
	}

	return nil
}

// validateIsPool validates that an address is a pool contract
func (d *ABIDecoder) validateIsPool(ctx context.Context, address common.Address) error {
	// Test for Uniswap V2/V3 pool functions
	poolFunctions := [][]byte{
		{0x0d, 0xfe, 0x16, 0x81}, // token0()
		{0xd2, 0x12, 0x20, 0xa7}, // token1()
	}

	successCount := 0
	for _, funcSig := range poolFunctions {
		_, err := d.client.CallContract(ctx, ethereum.CallMsg{
			To:   &address,
			Data: funcSig,
		}, nil)

		if err == nil {
			successCount++
		}
	}

	// Must support both token0() and token1() functions
	if successCount < 2 {
		return fmt.Errorf("address %s does not appear to be a pool contract (supported %d/2 pool functions)", address.Hex(), successCount)
	}

	// CRITICAL: Ensure it's not an ERC-20 token by testing token-specific functions
	if d.appearsToBeERC20(ctx, address) {
		return fmt.Errorf("address %s appears to be an ERC-20 token, not a pool contract", address.Hex())
	}

	return nil
}

// appearsToBePool checks if an address has pool-like characteristics
func (d *ABIDecoder) appearsToBePool(ctx context.Context, address common.Address) bool {
	poolFunctions := [][]byte{
		{0x0d, 0xfe, 0x16, 0x81}, // token0()
		{0xd2, 0x12, 0x20, 0xa7}, // token1()
		{0x09, 0x02, 0xf1, 0xac}, // getReserves() - V2
		{0x38, 0x50, 0xc7, 0xbd}, // slot0() - V3
	}

	successCount := 0
	for _, funcSig := range poolFunctions {
		_, err := d.client.CallContract(ctx, ethereum.CallMsg{
			To:   &address,
			Data: funcSig,
		}, nil)

		if err == nil {
			successCount++
		}
	}

	// If it supports 2+ pool functions, it's likely a pool
	return successCount >= 2
}

// appearsToBeERC20 checks if an address has ERC-20 token characteristics
func (d *ABIDecoder) appearsToBeERC20(ctx context.Context, address common.Address) bool {
	erc20Functions := [][]byte{
		{0x70, 0xa0, 0x82, 0x31}, // balanceOf(address)
		{0x31, 0x3c, 0xe5, 0x67}, // decimals()
		{0x95, 0xd8, 0x9b, 0x41}, // symbol()
		{0x18, 0x16, 0x0d, 0xdd}, // totalSupply()
	}

	successCount := 0
	for _, funcSig := range erc20Functions {
		testData := make([]byte, 4+32)
		copy(testData[:4], funcSig)

		_, err := d.client.CallContract(ctx, ethereum.CallMsg{
			To:   &address,
			Data: testData,
		}, nil)

		if err == nil {
			successCount++
		}
	}

	// If it supports 3+ ERC-20 functions, it's likely an ERC-20 token
	return successCount >= 3
}

// CalculatePoolAddress calculates pool address using CREATE2 for known factories
func (d *ABIDecoder) CalculatePoolAddress(tokenA, tokenB common.Address, fee *big.Int, protocol string) (common.Address, error) {
	// Arbitrum factory addresses
	factories := map[string]common.Address{
		"uniswap_v3": common.HexToAddress("0x1F98431c8aD98523631AE4a59f267346ea31F984"),
		"camelot_v3": common.HexToAddress("0x1a3c9B1d2F0529D97f2afC5136Cc23e58f1FD35B"),
		"sushiswap":  common.HexToAddress("0xc35DADB65012eC5796536bD9864eD8773aBc74C4"),
		"algebra":    common.HexToAddress("0x411b0fAcC3489691f28ad58c47006AF5E3Ab3A28"),
	}

	factory, exists := factories[protocol]
	if !exists {
		return common.Address{}, fmt.Errorf("unknown protocol: %s", protocol)
	}

	// Ensure token addresses are not zero addresses
	if tokenA == (common.Address{}) || tokenB == (common.Address{}) {
		return common.Address{}, fmt.Errorf("token addresses cannot be zero")
	}

	// Ensure token order (tokenA < tokenB)
	if tokenA.Big().Cmp(tokenB.Big()) > 0 {
		tokenA, tokenB = tokenB, tokenA
	}

	switch protocol {
	case "uniswap_v3", "camelot_v3":
		return d.calculateUniswapV3PoolAddress(factory, tokenA, tokenB, fee)
	case "sushiswap":
		return d.calculateUniswapV2PoolAddress(factory, tokenA, tokenB)
	default:
		return d.calculateUniswapV2PoolAddress(factory, tokenA, tokenB)
	}
}

// calculateUniswapV3PoolAddress calculates Uniswap V3 pool address
func (d *ABIDecoder) calculateUniswapV3PoolAddress(factory, tokenA, tokenB common.Address, fee *big.Int) (common.Address, error) {
	// Check if fee is nil and handle appropriately
	if fee == nil {
		fee = big.NewInt(0) // Use 0 as default fee if nil
	}

	// Ensure token addresses are not zero addresses
	if tokenA == (common.Address{}) || tokenB == (common.Address{}) {
		return common.Address{}, fmt.Errorf("token addresses cannot be zero")
	}

	// Ensure fee is never nil when calling fee.Bytes()
	feeBytes := common.LeftPadBytes(fee.Bytes(), 32)

	// Uniswap V3 CREATE2 salt: keccak256(abi.encode(token0, token1, fee))
	salt := crypto.Keccak256(
		common.LeftPadBytes(tokenA.Bytes(), 32),
		common.LeftPadBytes(tokenB.Bytes(), 32),
		feeBytes,
	)

	// Uniswap V3 pool init code hash
	initCodeHash := common.HexToHash("0xe34f199b19b2b4f47f68442619d555527d244f78a3297ea89325f843f87b8b54")

	// CREATE2 address calculation: keccak256(0xff ++ factory ++ salt ++ keccak256(initCode))[12:]
	data := make([]byte, 1+20+32+32)
	data[0] = 0xff
	copy(data[1:21], factory.Bytes())
	copy(data[21:53], salt)
	copy(data[53:85], initCodeHash.Bytes())

	hash := crypto.Keccak256(data)
	return common.BytesToAddress(hash[12:]), nil
}

// calculateUniswapV2PoolAddress calculates Uniswap V2 style pool address
func (d *ABIDecoder) calculateUniswapV2PoolAddress(factory, tokenA, tokenB common.Address) (common.Address, error) {
	// Uniswap V2 CREATE2 salt: keccak256(abi.encodePacked(token0, token1))
	salt := crypto.Keccak256(append(tokenA.Bytes(), tokenB.Bytes()...))

	// SushiSwap init code hash (example)
	initCodeHash := common.HexToHash("0xe18a34eb0e04b04f7a0ac29a6e80748dca96319b42c54d679cb821dca90c6303")

	// CREATE2 address calculation
	data := make([]byte, 1+20+32+32)
	data[0] = 0xff
	copy(data[1:21], factory.Bytes())
	copy(data[21:53], salt)
	copy(data[53:85], initCodeHash.Bytes())

	hash := crypto.Keccak256(data)
	return common.BytesToAddress(hash[12:]), nil
}

// decodeCurveSwap decodes Curve Finance swap transactions
func (d *ABIDecoder) decodeCurveSwap(data []byte, functionSig string) (*SwapParams, error) {
	params := &SwapParams{}
	data = data[4:] // Skip function selector

	if strings.Contains(functionSig, "exchange") {
		// Curve exchange(int128,int128,uint256,uint256) or exchange_underlying
		if len(data) >= 128 {
			// Skip token indices (first 64 bytes) and get amounts
			params.AmountIn = new(big.Int).SetBytes(data[64:96])
			params.MinAmountOut = new(big.Int).SetBytes(data[96:128])

			// For Curve, token addresses would need to be looked up from pool contract
			// For now, use placeholder logic from generic decoder
			return d.decodeGenericSwap(append([]byte{0, 0, 0, 0}, data...), "curve")
		}
	}

	return params, nil
}

// decodeLendingSwap decodes lending protocol transactions (Radiant, Aave, etc.)
func (d *ABIDecoder) decodeLendingSwap(data []byte, functionSig string) (*SwapParams, error) {
	params := &SwapParams{}
	data = data[4:] // Skip function selector

	if strings.Contains(functionSig, "deposit") || strings.Contains(functionSig, "withdraw") ||
		strings.Contains(functionSig, "borrow") || strings.Contains(functionSig, "repay") {
		// Standard lending operations: (asset, amount, onBehalfOf, referralCode)
		if len(data) >= 96 {
			params.TokenIn = common.BytesToAddress(data[0:32])    // asset
			params.AmountIn = new(big.Int).SetBytes(data[32:64])  // amount
			params.Recipient = common.BytesToAddress(data[64:96]) // onBehalfOf

			// For lending, TokenOut would be the receipt token (aToken, etc.)
			// This would need protocol-specific logic to determine
		}
	} else if strings.Contains(functionSig, "transfer") {
		// ERC-20 transfer/transferFrom
		if strings.Contains(functionSig, "transferFrom") && len(data) >= 96 {
			// transferFrom(from, to, amount)
			params.Recipient = common.BytesToAddress(data[32:64]) // to
			params.AmountIn = new(big.Int).SetBytes(data[64:96])  // amount
		} else if len(data) >= 64 {
			// transfer(to, amount)
			params.Recipient = common.BytesToAddress(data[0:32]) // to
			params.AmountIn = new(big.Int).SetBytes(data[32:64]) // amount
		}
	}

	return params, nil
}

// decodeGMXSwap decodes GMX protocol transactions
func (d *ABIDecoder) decodeGMXSwap(data []byte, functionSig string) (*SwapParams, error) {
	params := &SwapParams{}
	data = data[4:] // Skip function selector

	if strings.Contains(functionSig, "swap") {
		// GMX swap(address[],uint256,uint256,address)
		if len(data) >= 128 {
			// First parameter is path array offset, skip to amount
			params.AmountIn = new(big.Int).SetBytes(data[32:64])
			params.MinAmountOut = new(big.Int).SetBytes(data[64:96])
			params.Recipient = common.BytesToAddress(data[96:128])

			// Extract token path from the dynamic array
			// This would need more complex parsing for the path array
		}
	}

	// Fall back to generic decoding for complex GMX transactions
	return d.decodeGenericSwap(append([]byte{0, 0, 0, 0}, data...), "gmx")
}

// decodeMulticall decodes multicall transactions by extracting individual calls
func (d *ABIDecoder) decodeMulticall(data []byte, protocol string) (*SwapParams, error) {
	if len(data) < 4 {
		return nil, fmt.Errorf("insufficient data for multicall")
	}

	// Skip function selector
	data = data[4:]

	if len(data) < 32 {
		return nil, fmt.Errorf("insufficient data for multicall array offset")
	}

	// Get array offset
	arrayOffset := new(big.Int).SetBytes(data[0:32]).Uint64()

	if arrayOffset >= uint64(len(data)) || arrayOffset+32 >= uint64(len(data)) {
		return nil, fmt.Errorf("invalid array offset in multicall")
	}

	// Get array length
	arrayLength := new(big.Int).SetBytes(data[arrayOffset : arrayOffset+32]).Uint64()

	if arrayLength == 0 {
		return nil, fmt.Errorf("empty multicall array")
	}

	// SECURITY: Add maximum array length check to prevent DoS attacks
	// Limit to 1000 calls per multicall (reasonable for legitimate transactions)
	if arrayLength > 1000 {
		return nil, fmt.Errorf("multicall array length %d exceeds maximum 1000 (potential DoS)", arrayLength)
	}

	// Parse individual calls in the multicall
	bestParams := &SwapParams{}
	callsFound := 0

	for i := uint64(0); i < arrayLength; i++ {
		// Each call has an offset pointer
		offsetPos := arrayOffset + 32 + i*32
		if offsetPos+32 > uint64(len(data)) {
			break
		}

		callOffset := arrayOffset + new(big.Int).SetBytes(data[offsetPos:offsetPos+32]).Uint64()
		if callOffset+32 > uint64(len(data)) {
			continue
		}

		// Get call data length
		callDataLength := new(big.Int).SetBytes(data[callOffset : callOffset+32]).Uint64()
		if callOffset+32+callDataLength > uint64(len(data)) {
			continue
		}

		// Extract call data
		callData := data[callOffset+32 : callOffset+32+callDataLength]
		if len(callData) < 4 {
			continue
		}

		// Try to decode this individual call
		params, err := d.decodeIndividualCall(callData, protocol)
		if err == nil && params != nil {
			callsFound++
			// Use the first successfully decoded call or the one with most complete data
			if bestParams.TokenIn == (common.Address{}) ||
				(params.TokenIn != (common.Address{}) && params.TokenOut != (common.Address{})) {
				bestParams = params
			}
		}
	}

	if callsFound == 0 {
		return nil, fmt.Errorf("no decodable calls found in multicall")
	}

	return bestParams, nil
}

// decodeIndividualCall decodes an individual call within a multicall
func (d *ABIDecoder) decodeIndividualCall(callData []byte, protocol string) (*SwapParams, error) {
	if len(callData) < 4 {
		return nil, fmt.Errorf("insufficient call data")
	}

	// Extract function selector
	selector := "0x" + hex.EncodeToString(callData[:4])

	// Check if this is a known swap function
	functionSig, exists := d.functionSignatures[selector]
	if !exists {
		// Try generic decoding for unknown functions
		return d.decodeGenericSwap(callData, protocol)
	}

	// Decode based on function signature
	if strings.Contains(functionSig, "swapExact") || strings.Contains(functionSig, "exactInput") {
		// This is a swap function, decode it appropriately
		switch {
		case strings.Contains(functionSig, "exactInputSingle"):
			return d.decodeUniswapV3Swap(callData, functionSig)
		case strings.Contains(functionSig, "exactInput"):
			return d.decodeUniswapV3Swap(callData, functionSig)
		case strings.Contains(functionSig, "swapExactTokensForTokens"):
			return d.decodeUniswapV2Swap(callData, functionSig)
		case strings.Contains(functionSig, "swapTokensForExactTokens"):
			return d.decodeUniswapV2Swap(callData, functionSig)
		case strings.Contains(functionSig, "swapExactETHForTokens"):
			return d.decodeUniswapV2Swap(callData, functionSig)
		case strings.Contains(functionSig, "swapExactTokensForETH"):
			return d.decodeUniswapV2Swap(callData, functionSig)
		default:
			return d.decodeGenericSwap(callData, protocol)
		}
	}

	// Not a swap function, try generic decoding
	return d.decodeGenericSwap(callData, protocol)
}