mev-beta/pkg/profitcalc/slippage_protection.go

package profitcalc

import (
	"fmt"
	"math/big"

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

// SlippageProtector provides slippage calculation and protection for arbitrage trades
type SlippageProtector struct {
	logger          *logger.Logger
	maxSlippageBps  int64   // Maximum allowed slippage in basis points
	liquidityBuffer float64 // Buffer factor for liquidity calculations
}

// SlippageAnalysis contains detailed slippage analysis for a trade
type SlippageAnalysis struct {
	TradeAmount       *big.Float // Amount being traded
	PoolLiquidity     *big.Float // Available liquidity in pool
	EstimatedSlippage float64    // Estimated slippage percentage
	SlippageBps       int64      // Slippage in basis points
	PriceImpact       float64    // Price impact percentage
	EffectivePrice    *big.Float // Price after slippage
	MinAmountOut      *big.Float // Minimum amount out with slippage protection
	IsAcceptable      bool       // Whether slippage is within acceptable limits
	RiskLevel         string     // "Low", "Medium", "High", "Extreme"
	Recommendation    string     // Trading recommendation
}

// NewSlippageProtector creates a new slippage protection manager
func NewSlippageProtector(logger *logger.Logger) *SlippageProtector {
	return &SlippageProtector{
		logger:          logger,
		maxSlippageBps:  500, // 5% maximum slippage
		liquidityBuffer: 0.8, // Use 80% of available liquidity for calculations
	}
}

// AnalyzeSlippage performs comprehensive slippage analysis for a potential trade
func (sp *SlippageProtector) AnalyzeSlippage(
	tradeAmount *big.Float,
	poolLiquidity *big.Float,
	currentPrice *big.Float,
) *SlippageAnalysis {

	if tradeAmount == nil || poolLiquidity == nil || currentPrice == nil {
		return &SlippageAnalysis{
			IsAcceptable:   false,
			RiskLevel:      "Extreme",
			Recommendation: "Insufficient data for slippage calculation",
		}
	}

	// Calculate trade size as percentage of pool liquidity
	tradeSizeRatio := new(big.Float).Quo(tradeAmount, poolLiquidity)
	tradeSizeFloat, _ := tradeSizeRatio.Float64()

	// CRITICAL FIX: Use proper constant product AMM formula
	// Bug: Old formula "tradeSize / 2.0" is mathematically incorrect
	// Correct Uniswap V2 formula: dy = (y * dx * 997) / (x * 1000 + dx * 997)
	// Slippage = (marketPrice - executionPrice) / marketPrice
	estimatedSlippage := sp.calculateConstantProductSlippage(tradeAmount, poolLiquidity, currentPrice)

	slippageBps := int64(estimatedSlippage * 10000)

	// Calculate price impact (similar to slippage but different calculation)
	priceImpact := sp.calculatePriceImpact(tradeSizeFloat)

	// Calculate effective price after slippage
	slippageFactor := 1.0 - estimatedSlippage
	effectivePrice := new(big.Float).Mul(currentPrice, big.NewFloat(slippageFactor))

	// Calculate minimum amount out with slippage protection
	minAmountOut := new(big.Float).Quo(tradeAmount, effectivePrice)

	// Determine risk level and acceptability
	riskLevel, isAcceptable := sp.assessRiskLevel(slippageBps, tradeSizeFloat)
	recommendation := sp.generateRecommendation(slippageBps, tradeSizeFloat, riskLevel)

	analysis := &SlippageAnalysis{
		TradeAmount:       tradeAmount,
		PoolLiquidity:     poolLiquidity,
		EstimatedSlippage: estimatedSlippage,
		SlippageBps:       slippageBps,
		PriceImpact:       priceImpact,
		EffectivePrice:    effectivePrice,
		MinAmountOut:      minAmountOut,
		IsAcceptable:      isAcceptable,
		RiskLevel:         riskLevel,
		Recommendation:    recommendation,
	}

	sp.logger.Debug(fmt.Sprintf("Slippage analysis: Trade=%s, Liquidity=%s, Slippage=%.2f%%, Risk=%s",
		tradeAmount.String(), poolLiquidity.String(), estimatedSlippage*100, riskLevel))

	return analysis
}

// calculateConstantProductSlippage calculates slippage using correct Uniswap V2 constant product formula
// Formula: dy = (y * dx * 997) / (x * 1000 + dx * 997)
// Where: x = reserveIn, y = reserveOut, dx = amountIn, dy = amountOut
// Slippage = (marketPrice - executionPrice) / marketPrice
func (sp *SlippageProtector) calculateConstantProductSlippage(
	amountIn *big.Float,
	reserveIn *big.Float,
	marketPrice *big.Float,
) float64 {
	// Handle edge cases
	if amountIn == nil || reserveIn == nil || marketPrice == nil {
		return 1.0 // 100% slippage for invalid inputs
	}
	if amountIn.Sign() <= 0 || reserveIn.Sign() <= 0 || marketPrice.Sign() <= 0 {
		return 1.0
	}

	// Calculate: dx * 997 (Uniswap V2 fee is 0.3%, so 997/1000 remains)
	fee := big.NewFloat(997)
	dx997 := new(big.Float).Mul(amountIn, fee)

	// Calculate: x * 1000
	x1000 := new(big.Float).Mul(reserveIn, big.NewFloat(1000))

	// Calculate: x * 1000 + dx * 997
	denominator := new(big.Float).Add(x1000, dx997)

	// Calculate execution price = dx / (x * 1000 + dx * 997)
	// This represents how much the price moved
	executionRatio := new(big.Float).Quo(dx997, denominator)

	// For small trades, slippage ≈ executionRatio / 2
	// For larger trades, use more precise calculation
	tradeSizeRatio := new(big.Float).Quo(amountIn, reserveIn)
	tradeSizeFloat, _ := tradeSizeRatio.Float64()

	var slippage float64
	if tradeSizeFloat < 0.01 { // < 1% of pool
		// Linear approximation for small trades
		ratioFloat, _ := executionRatio.Float64()
		slippage = ratioFloat / 2.0
	} else {
		// Full calculation for larger trades
		// Slippage = (marketPrice - executionPrice) / marketPrice
		// executionPrice = dy / dx = (y * 997) / (x * 1000 + dx * 997)
		// Simplified: slippage ≈ dx / (2 * (x + dx/2))

		halfDx := new(big.Float).Quo(amountIn, big.NewFloat(2))
		reservePlusHalfDx := new(big.Float).Add(reserveIn, halfDx)
		twoTimesReservePlusHalfDx := new(big.Float).Mul(reservePlusHalfDx, big.NewFloat(2))
		slippageFloat := new(big.Float).Quo(amountIn, twoTimesReservePlusHalfDx)
		slippage, _ = slippageFloat.Float64()

		// Apply fee adjustment (0.3% fee adds to effective slippage)
		slippage += 0.003
	}

	// Cap at 100%
	if slippage > 1.0 {
		slippage = 1.0
	} else if slippage < 0 {
		slippage = 0
	}

	return slippage
}

// calculatePriceImpact calculates price impact using AMM mechanics
func (sp *SlippageProtector) calculatePriceImpact(tradeSizeRatio float64) float64 {
	// For constant product AMMs (like Uniswap V2):
	// Price impact = trade_size / (1 + trade_size)
	priceImpact := tradeSizeRatio / (1.0 + tradeSizeRatio)

	// Cap at 100%
	if priceImpact > 1.0 {
		priceImpact = 1.0
	}

	return priceImpact
}

// assessRiskLevel determines risk level based on slippage and trade size
func (sp *SlippageProtector) assessRiskLevel(slippageBps int64, tradeSizeRatio float64) (string, bool) {
	isAcceptable := slippageBps <= sp.maxSlippageBps

	var riskLevel string
	switch {
	case slippageBps <= 50: // <= 0.5%
		riskLevel = "Low"
	case slippageBps <= 200: // <= 2%
		riskLevel = "Medium"
	case slippageBps <= 500: // <= 5%
		riskLevel = "High"
	default:
		riskLevel = "Extreme"
		isAcceptable = false
	}

	// Additional checks for trade size
	if tradeSizeRatio > 0.5 { // > 50% of pool
		riskLevel = "Extreme"
		isAcceptable = false
	} else if tradeSizeRatio > 0.2 { // > 20% of pool
		if riskLevel == "Low" {
			riskLevel = "Medium"
		} else if riskLevel == "Medium" {
			riskLevel = "High"
		}
	}

	return riskLevel, isAcceptable
}

// generateRecommendation provides trading recommendations based on analysis
func (sp *SlippageProtector) generateRecommendation(slippageBps int64, tradeSizeRatio float64, riskLevel string) string {
	switch riskLevel {
	case "Low":
		return "Safe to execute - low slippage expected"
	case "Medium":
		if tradeSizeRatio > 0.1 {
			return "Consider splitting trade into smaller parts"
		}
		return "Proceed with caution - moderate slippage expected"
	case "High":
		return "High slippage risk - consider reducing trade size or finding alternative routes"
	case "Extreme":
		if tradeSizeRatio > 0.5 {
			return "Trade too large for pool - split into multiple smaller trades"
		}
		return "Excessive slippage - avoid this trade"
	default:
		return "Unable to assess - insufficient data"
	}
}

// CalculateOptimalTradeSize calculates optimal trade size to stay within slippage limits
func (sp *SlippageProtector) CalculateOptimalTradeSize(
	poolLiquidity *big.Float,
	maxSlippageBps int64,
) *big.Float {

	if poolLiquidity == nil || poolLiquidity.Sign() <= 0 {
		return big.NewFloat(0)
	}

	// Convert max slippage to ratio
	maxSlippageRatio := float64(maxSlippageBps) / 10000.0

	// For simplified AMM: optimal_trade_size = 2 * liquidity * max_slippage
	optimalRatio := 2.0 * maxSlippageRatio

	// Apply safety factor
	safetyFactor := 0.8 // Use 80% of optimal to be conservative
	optimalRatio *= safetyFactor

	optimalSize := new(big.Float).Mul(poolLiquidity, big.NewFloat(optimalRatio))

	sp.logger.Debug(fmt.Sprintf("Calculated optimal trade size: %s (%.2f%% of pool) for max slippage %d bps",
		optimalSize.String(), optimalRatio*100, maxSlippageBps))

	return optimalSize
}

// EstimateGasForSlippage estimates additional gas needed for slippage protection
func (sp *SlippageProtector) EstimateGasForSlippage(analysis *SlippageAnalysis) uint64 {
	baseGas := uint64(0)

	// Higher slippage might require more complex routing
	switch analysis.RiskLevel {
	case "Low":
		baseGas = 0 // No additional gas
	case "Medium":
		baseGas = 20000 // Additional gas for price checks
	case "High":
		baseGas = 50000 // Additional gas for complex routing
	case "Extreme":
		baseGas = 100000 // Maximum additional gas for emergency handling
	}

	return baseGas
}

// SetMaxSlippage updates the maximum allowed slippage
func (sp *SlippageProtector) SetMaxSlippage(bps int64) {
	sp.maxSlippageBps = bps
	sp.logger.Info(fmt.Sprintf("Updated maximum slippage to %d bps (%.2f%%)", bps, float64(bps)/100))
}

// GetMaxSlippage returns the current maximum slippage setting
func (sp *SlippageProtector) GetMaxSlippage() int64 {
	return sp.maxSlippageBps
}

// ValidateTradeParameters performs comprehensive validation of trade parameters
func (sp *SlippageProtector) ValidateTradeParameters(
	tradeAmount *big.Float,
	poolLiquidity *big.Float,
	minLiquidity *big.Float,
) error {

	if tradeAmount == nil || tradeAmount.Sign() <= 0 {
		return fmt.Errorf("invalid trade amount: must be positive")
	}

	if poolLiquidity == nil || poolLiquidity.Sign() <= 0 {
		return fmt.Errorf("invalid pool liquidity: must be positive")
	}

	if minLiquidity != nil && poolLiquidity.Cmp(minLiquidity) < 0 {
		return fmt.Errorf("insufficient pool liquidity: %s < %s required",
			poolLiquidity.String(), minLiquidity.String())
	}

	// Check if trade is reasonable relative to pool size
	tradeSizeRatio := new(big.Float).Quo(tradeAmount, poolLiquidity)
	tradeSizeFloat, _ := tradeSizeRatio.Float64()

	if tradeSizeFloat > 0.9 { // > 90% of pool
		return fmt.Errorf("trade size too large: %.1f%% of pool liquidity", tradeSizeFloat*100)
	}

	return nil
}

// CalculateSlippageAdjustedProfit adjusts profit calculations for slippage
func (sp *SlippageProtector) CalculateSlippageAdjustedProfit(
	grossProfit *big.Float,
	analysis *SlippageAnalysis,
) *big.Float {

	if grossProfit == nil || analysis == nil {
		return big.NewFloat(0)
	}

	// Reduce profit by estimated slippage impact
	slippageImpact := big.NewFloat(analysis.EstimatedSlippage)
	slippageReduction := new(big.Float).Mul(grossProfit, slippageImpact)
	adjustedProfit := new(big.Float).Sub(grossProfit, slippageReduction)

	// Ensure profit doesn't go negative due to slippage
	if adjustedProfit.Sign() < 0 {
		adjustedProfit = big.NewFloat(0)
	}

	sp.logger.Debug(fmt.Sprintf("Slippage-adjusted profit: %s -> %s (reduction: %s)",
		grossProfit.String(), adjustedProfit.String(), slippageReduction.String()))

	return adjustedProfit
}