mev-beta/pkg/parsers/arbiscan_validator.go

package parsers

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"math/big"
	"net/http"
	"net/url"
	"strings"
	"time"

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

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

// ArbiscanValidator validates parsed swap events against Arbiscan API
type ArbiscanValidator struct {
	apiKey     string
	baseURL    string
	httpClient *http.Client
	logger     types.Logger
	swapLogger *SwapLogger
}

// ArbiscanLog represents a log entry from Arbiscan API
type ArbiscanLog struct {
	Address          string   `json:"address"`
	Topics           []string `json:"topics"`
	Data             string   `json:"data"`
	BlockNumber      string   `json:"blockNumber"`
	TimeStamp        string   `json:"timeStamp"`
	GasPrice         string   `json:"gasPrice"`
	GasUsed          string   `json:"gasUsed"`
	LogIndex         string   `json:"logIndex"`
	TransactionHash  string   `json:"transactionHash"`
	TransactionIndex string   `json:"transactionIndex"`
}

// ArbiscanAPIResponse represents the API response from Arbiscan
type ArbiscanAPIResponse struct {
	Status  string        `json:"status"`
	Message string        `json:"message"`
	Result  []ArbiscanLog `json:"result"`
}

// ValidationResult contains the result of validating a swap event
type ValidationResult struct {
	IsValid      bool                  `json:"is_valid"`
	SwapEvent    *types.SwapEvent      `json:"swap_event"`
	ArbiscanLog  *ArbiscanLog          `json:"arbiscan_log"`
	Discrepancies []string             `json:"discrepancies,omitempty"`
	ValidatedAt  time.Time             `json:"validated_at"`
}

// NewArbiscanValidator creates a new Arbiscan validator
func NewArbiscanValidator(apiKey string, logger types.Logger, swapLogger *SwapLogger) *ArbiscanValidator {
	return &ArbiscanValidator{
		apiKey:  apiKey,
		baseURL: "https://api.arbiscan.io/api",
		httpClient: &http.Client{
			Timeout: 10 * time.Second,
		},
		logger:     logger,
		swapLogger: swapLogger,
	}
}

// ValidateSwap validates a parsed swap event against Arbiscan
func (v *ArbiscanValidator) ValidateSwap(ctx context.Context, event *types.SwapEvent) (*ValidationResult, error) {
	// Fetch transaction logs from Arbiscan
	logs, err := v.getTransactionLogs(ctx, event.TxHash)
	if err != nil {
		return nil, fmt.Errorf("failed to fetch logs from Arbiscan: %w", err)
	}

	// Find the matching log by log index
	var matchingLog *ArbiscanLog
	for i := range logs {
		logIndex := parseHexToUint64(logs[i].LogIndex)
		if logIndex == uint64(event.LogIndex) {
			matchingLog = &logs[i]
			break
		}
	}

	if matchingLog == nil {
		return &ValidationResult{
			IsValid:      false,
			SwapEvent:    event,
			Discrepancies: []string{fmt.Sprintf("log index %d not found in Arbiscan response", event.LogIndex)},
			ValidatedAt:  time.Now(),
		}, nil
	}

	// Compare parsed event with Arbiscan data
	discrepancies := v.compareSwapWithArbiscan(event, matchingLog)

	result := &ValidationResult{
		IsValid:      len(discrepancies) == 0,
		SwapEvent:    event,
		ArbiscanLog:  matchingLog,
		Discrepancies: discrepancies,
		ValidatedAt:  time.Now(),
	}

	// Log validation result
	if len(discrepancies) > 0 {
		v.logger.Warn("swap validation discrepancies found",
			"txHash", event.TxHash.Hex(),
			"logIndex", event.LogIndex,
			"discrepancies", strings.Join(discrepancies, "; "),
		)

		// Save discrepancy to swap logger for investigation
		if v.swapLogger != nil {
			rawData := common.Hex2Bytes(strings.TrimPrefix(matchingLog.Data, "0x"))
			if err := v.swapLogger.LogSwap(ctx, event, rawData, matchingLog.Topics, "arbiscan_validation"); err != nil {
				v.logger.Error("failed to log discrepancy", "error", err)
			}
		}
	} else {
		v.logger.Debug("swap validation successful",
			"txHash", event.TxHash.Hex(),
			"logIndex", event.LogIndex,
		)
	}

	return result, nil
}

// getTransactionLogs fetches transaction logs from Arbiscan API
func (v *ArbiscanValidator) getTransactionLogs(ctx context.Context, txHash common.Hash) ([]ArbiscanLog, error) {
	// Build API URL
	params := url.Values{}
	params.Set("module", "logs")
	params.Set("action", "getLogs")
	params.Set("txhash", txHash.Hex())
	params.Set("apikey", v.apiKey)

	apiURL := fmt.Sprintf("%s?%s", v.baseURL, params.Encode())

	// Create request
	req, err := http.NewRequestWithContext(ctx, "GET", apiURL, nil)
	if err != nil {
		return nil, fmt.Errorf("failed to create request: %w", err)
	}

	// Execute request
	resp, err := v.httpClient.Do(req)
	if err != nil {
		return nil, fmt.Errorf("failed to execute request: %w", err)
	}
	defer resp.Body.Close()

	// Read response
	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, fmt.Errorf("failed to read response: %w", err)
	}

	// Parse response
	var apiResp ArbiscanAPIResponse
	if err := json.Unmarshal(body, &apiResp); err != nil {
		return nil, fmt.Errorf("failed to parse response: %w", err)
	}

	if apiResp.Status != "1" {
		return nil, fmt.Errorf("Arbiscan API error: %s", apiResp.Message)
	}

	return apiResp.Result, nil
}

// compareSwapWithArbiscan compares a parsed swap event with Arbiscan log data
func (v *ArbiscanValidator) compareSwapWithArbiscan(event *types.SwapEvent, log *ArbiscanLog) []string {
	var discrepancies []string

	// Compare pool address
	if !strings.EqualFold(event.PoolAddress.Hex(), log.Address) {
		discrepancies = append(discrepancies, fmt.Sprintf(
			"pool address mismatch: parsed=%s arbiscan=%s",
			event.PoolAddress.Hex(), log.Address,
		))
	}

	// Compare transaction hash
	if !strings.EqualFold(event.TxHash.Hex(), log.TransactionHash) {
		discrepancies = append(discrepancies, fmt.Sprintf(
			"tx hash mismatch: parsed=%s arbiscan=%s",
			event.TxHash.Hex(), log.TransactionHash,
		))
	}

	// Compare block number
	arbiscanBlockNumber := parseHexToUint64(log.BlockNumber)
	if event.BlockNumber != arbiscanBlockNumber {
		discrepancies = append(discrepancies, fmt.Sprintf(
			"block number mismatch: parsed=%d arbiscan=%d",
			event.BlockNumber, arbiscanBlockNumber,
		))
	}

	// Compare log index
	arbiscanLogIndex := parseHexToUint64(log.LogIndex)
	if uint64(event.LogIndex) != arbiscanLogIndex {
		discrepancies = append(discrepancies, fmt.Sprintf(
			"log index mismatch: parsed=%d arbiscan=%d",
			event.LogIndex, arbiscanLogIndex,
		))
	}

	// Compare topics (event signature and indexed parameters)
	if len(log.Topics) > 0 {
		expectedSignature := log.Topics[0]
		// UniswapV2 Swap signature
		if strings.EqualFold(expectedSignature, SwapEventSignature.Hex()) {
			// Validate sender and recipient from topics
			if len(log.Topics) >= 3 {
				arbiscanSender := common.HexToAddress(log.Topics[1])
				arbiscanRecipient := common.HexToAddress(log.Topics[2])

				if event.Sender != arbiscanSender {
					discrepancies = append(discrepancies, fmt.Sprintf(
						"sender mismatch: parsed=%s arbiscan=%s",
						event.Sender.Hex(), arbiscanSender.Hex(),
					))
				}

				if event.Recipient != arbiscanRecipient {
					discrepancies = append(discrepancies, fmt.Sprintf(
						"recipient mismatch: parsed=%s arbiscan=%s",
						event.Recipient.Hex(), arbiscanRecipient.Hex(),
					))
				}
			}
		}
	}

	// Note: We don't compare amounts directly here because they're scaled
	// and Arbiscan returns raw values. The caller should handle amount validation
	// by comparing raw log data if needed.

	return discrepancies
}

// ValidateSwapBatch validates multiple swap events from the same transaction
func (v *ArbiscanValidator) ValidateSwapBatch(ctx context.Context, events []*types.SwapEvent) ([]*ValidationResult, error) {
	if len(events) == 0 {
		return nil, nil
	}

	// All events should have the same transaction hash
	txHash := events[0].TxHash

	// Fetch transaction logs once for all events
	logs, err := v.getTransactionLogs(ctx, txHash)
	if err != nil {
		return nil, fmt.Errorf("failed to fetch logs from Arbiscan: %w", err)
	}

	// Validate each event
	results := make([]*ValidationResult, 0, len(events))
	for _, event := range events {
		// Find matching log
		var matchingLog *ArbiscanLog
		for i := range logs {
			logIndex := parseHexToUint64(logs[i].LogIndex)
			if logIndex == uint64(event.LogIndex) {
				matchingLog = &logs[i]
				break
			}
		}

		if matchingLog == nil {
			results = append(results, &ValidationResult{
				IsValid:      false,
				SwapEvent:    event,
				Discrepancies: []string{fmt.Sprintf("log index %d not found", event.LogIndex)},
				ValidatedAt:  time.Now(),
			})
			continue
		}

		// Compare
		discrepancies := v.compareSwapWithArbiscan(event, matchingLog)
		results = append(results, &ValidationResult{
			IsValid:      len(discrepancies) == 0,
			SwapEvent:    event,
			ArbiscanLog:  matchingLog,
			Discrepancies: discrepancies,
			ValidatedAt:  time.Now(),
		})
	}

	return results, nil
}

// parseHexToUint64 parses a hex string to uint64
func parseHexToUint64(hex string) uint64 {
	if strings.HasPrefix(hex, "0x") {
		hex = hex[2:]
	}
	n := new(big.Int)
	n.SetString(hex, 16)
	return n.Uint64()
}

// GetValidationStats returns validation statistics
type ValidationStats struct {
	TotalValidated int       `json:"total_validated"`
	Valid          int       `json:"valid"`
	Invalid        int       `json:"invalid"`
	ErrorRate      float64   `json:"error_rate"`
	LastValidated  time.Time `json:"last_validated"`
}

// Note: To use this validator in production:
// 1. Create validator: validator := NewArbiscanValidator(apiKey, logger, swapLogger)
// 2. After parsing a swap: result, err := validator.ValidateSwap(ctx, event)
// 3. Check result.IsValid and log discrepancies
// 4. Use for spot-checking in production or continuous validation in testing