mev-beta/pkg/dex/decoder.go

package dex

import (
	"context"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/ethclient"
	"math/big"
)

// DEXDecoder is the interface that all DEX protocol decoders must implement
type DEXDecoder interface {
	// DecodeSwap decodes a swap transaction
	DecodeSwap(tx *types.Transaction) (*SwapInfo, error)

	// GetPoolReserves fetches current pool reserves
	GetPoolReserves(ctx context.Context, client *ethclient.Client, poolAddress common.Address) (*PoolReserves, error)

	// CalculateOutput calculates the expected output for a given input
	CalculateOutput(amountIn *big.Int, reserves *PoolReserves, tokenIn common.Address) (*big.Int, error)

	// CalculatePriceImpact calculates the price impact of a trade
	CalculatePriceImpact(amountIn *big.Int, reserves *PoolReserves, tokenIn common.Address) (float64, error)

	// GetQuote gets a price quote for a swap
	GetQuote(ctx context.Context, client *ethclient.Client, tokenIn, tokenOut common.Address, amountIn *big.Int) (*PriceQuote, error)

	// IsValidPool checks if a pool address is valid for this DEX
	IsValidPool(ctx context.Context, client *ethclient.Client, poolAddress common.Address) (bool, error)

	// GetProtocol returns the protocol this decoder handles
	GetProtocol() DEXProtocol
}

// BaseDecoder provides common functionality for all decoders
type BaseDecoder struct {
	protocol DEXProtocol
	client   *ethclient.Client
}

// NewBaseDecoder creates a new base decoder
func NewBaseDecoder(protocol DEXProtocol, client *ethclient.Client) *BaseDecoder {
	return &BaseDecoder{
		protocol: protocol,
		client:   client,
	}
}

// GetProtocol returns the protocol
func (bd *BaseDecoder) GetProtocol() DEXProtocol {
	return bd.protocol
}

// CalculatePriceImpact is a default implementation of price impact calculation
// This works for constant product AMMs (UniswapV2, SushiSwap)
func (bd *BaseDecoder) CalculatePriceImpact(amountIn *big.Int, reserves *PoolReserves, tokenIn common.Address) (float64, error) {
	if amountIn == nil || amountIn.Sign() <= 0 {
		return 0, nil
	}

	var reserveIn, reserveOut *big.Int
	if tokenIn == reserves.Token0 {
		reserveIn = reserves.Reserve0
		reserveOut = reserves.Reserve1
	} else {
		reserveIn = reserves.Reserve1
		reserveOut = reserves.Reserve0
	}

	if reserveIn.Sign() == 0 || reserveOut.Sign() == 0 {
		return 1.0, nil // 100% price impact if no liquidity
	}

	// Price before = reserveOut / reserveIn
	// Price after = newReserveOut / newReserveIn
	// Price impact = (priceAfter - priceBefore) / priceBefore

	// Calculate expected output using constant product formula
	amountInWithFee := new(big.Int).Mul(amountIn, big.NewInt(997)) // 0.3% fee
	numerator := new(big.Int).Mul(amountInWithFee, reserveOut)
	denominator := new(big.Int).Add(
		new(big.Int).Mul(reserveIn, big.NewInt(1000)),
		amountInWithFee,
	)
	amountOut := new(big.Int).Div(numerator, denominator)

	// Calculate price impact
	priceBefore := new(big.Float).Quo(
		new(big.Float).SetInt(reserveOut),
		new(big.Float).SetInt(reserveIn),
	)

	newReserveIn := new(big.Int).Add(reserveIn, amountIn)
	newReserveOut := new(big.Int).Sub(reserveOut, amountOut)

	priceAfter := new(big.Float).Quo(
		new(big.Float).SetInt(newReserveOut),
		new(big.Float).SetInt(newReserveIn),
	)

	impact := new(big.Float).Quo(
		new(big.Float).Sub(priceAfter, priceBefore),
		priceBefore,
	)

	impactFloat, _ := impact.Float64()
	return impactFloat, nil
}