mev-beta/pkg/dex/curve.go

package dex

import (
	"context"
	"fmt"
	"math/big"
	"strings"

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

// CurveDecoder implements DEXDecoder for Curve Finance (StableSwap)
type CurveDecoder struct {
	*BaseDecoder
	poolABI abi.ABI
}

// Curve StableSwap Pool ABI (minimal)
const curvePoolABI = `[
	{
		"name": "get_dy",
		"outputs": [{"type": "uint256", "name": ""}],
		"inputs": [
			{"type": "int128", "name": "i"},
			{"type": "int128", "name": "j"},
			{"type": "uint256", "name": "dx"}
		],
		"stateMutability": "view",
		"type": "function"
	},
	{
		"name": "exchange",
		"outputs": [{"type": "uint256", "name": ""}],
		"inputs": [
			{"type": "int128", "name": "i"},
			{"type": "int128", "name": "j"},
			{"type": "uint256", "name": "dx"},
			{"type": "uint256", "name": "min_dy"}
		],
		"stateMutability": "payable",
		"type": "function"
	},
	{
		"name": "coins",
		"outputs": [{"type": "address", "name": ""}],
		"inputs": [{"type": "uint256", "name": "arg0"}],
		"stateMutability": "view",
		"type": "function"
	},
	{
		"name": "balances",
		"outputs": [{"type": "uint256", "name": ""}],
		"inputs": [{"type": "uint256", "name": "arg0"}],
		"stateMutability": "view",
		"type": "function"
	},
	{
		"name": "A",
		"outputs": [{"type": "uint256", "name": ""}],
		"inputs": [],
		"stateMutability": "view",
		"type": "function"
	},
	{
		"name": "fee",
		"outputs": [{"type": "uint256", "name": ""}],
		"inputs": [],
		"stateMutability": "view",
		"type": "function"
	}
]`

// NewCurveDecoder creates a new Curve decoder
func NewCurveDecoder(client *ethclient.Client) *CurveDecoder {
	poolABI, _ := abi.JSON(strings.NewReader(curvePoolABI))

	return &CurveDecoder{
		BaseDecoder: NewBaseDecoder(ProtocolCurve, client),
		poolABI:     poolABI,
	}
}

// DecodeSwap decodes a Curve swap transaction
func (d *CurveDecoder) DecodeSwap(tx *types.Transaction) (*SwapInfo, error) {
	data := tx.Data()
	if len(data) < 4 {
		return nil, fmt.Errorf("transaction data too short")
	}

	method, err := d.poolABI.MethodById(data[:4])
	if err != nil {
		return nil, fmt.Errorf("failed to get method: %w", err)
	}

	if method.Name != "exchange" {
		return nil, fmt.Errorf("unsupported method: %s", method.Name)
	}

	params := make(map[string]interface{})
	if err := method.Inputs.UnpackIntoMap(params, data[4:]); err != nil {
		return nil, fmt.Errorf("failed to unpack params: %w", err)
	}

	// Curve uses indices for tokens, need to fetch actual addresses
	// This is a simplified version - production would cache token addresses
	poolAddress := *tx.To()

	return &SwapInfo{
		Protocol:    ProtocolCurve,
		PoolAddress: poolAddress,
		AmountIn:    params["dx"].(*big.Int),
		AmountOut:   params["min_dy"].(*big.Int),
		Fee:         big.NewInt(4), // 0.04% typical Curve fee
	}, nil
}

// GetPoolReserves fetches current pool reserves for Curve
func (d *CurveDecoder) GetPoolReserves(ctx context.Context, client *ethclient.Client, poolAddress common.Address) (*PoolReserves, error) {
	// Get amplification coefficient A
	aData, err := client.CallContract(ctx, ethereum.CallMsg{
		To:   &poolAddress,
		Data: d.poolABI.Methods["A"].ID,
	}, nil)
	if err != nil {
		return nil, fmt.Errorf("failed to get A: %w", err)
	}
	amplificationCoeff := new(big.Int).SetBytes(aData)

	// Get fee
	feeData, err := client.CallContract(ctx, ethereum.CallMsg{
		To:   &poolAddress,
		Data: d.poolABI.Methods["fee"].ID,
	}, nil)
	if err != nil {
		return nil, fmt.Errorf("failed to get fee: %w", err)
	}
	fee := new(big.Int).SetBytes(feeData)

	// Get token0 (index 0)
	token0Calldata, err := d.poolABI.Pack("coins", big.NewInt(0))
	if err != nil {
		return nil, fmt.Errorf("failed to pack coins(0): %w", err)
	}
	token0Data, err := client.CallContract(ctx, ethereum.CallMsg{
		To:   &poolAddress,
		Data: token0Calldata,
	}, nil)
	if err != nil {
		return nil, fmt.Errorf("failed to get token0: %w", err)
	}
	token0 := common.BytesToAddress(token0Data)

	// Get token1 (index 1)
	token1Calldata, err := d.poolABI.Pack("coins", big.NewInt(1))
	if err != nil {
		return nil, fmt.Errorf("failed to pack coins(1): %w", err)
	}
	token1Data, err := client.CallContract(ctx, ethereum.CallMsg{
		To:   &poolAddress,
		Data: token1Calldata,
	}, nil)
	if err != nil {
		return nil, fmt.Errorf("failed to get token1: %w", err)
	}
	token1 := common.BytesToAddress(token1Data)

	// Get balance0
	balance0Calldata, err := d.poolABI.Pack("balances", big.NewInt(0))
	if err != nil {
		return nil, fmt.Errorf("failed to pack balances(0): %w", err)
	}
	balance0Data, err := client.CallContract(ctx, ethereum.CallMsg{
		To:   &poolAddress,
		Data: balance0Calldata,
	}, nil)
	if err != nil {
		return nil, fmt.Errorf("failed to get balance0: %w", err)
	}
	reserve0 := new(big.Int).SetBytes(balance0Data)

	// Get balance1
	balance1Calldata, err := d.poolABI.Pack("balances", big.NewInt(1))
	if err != nil {
		return nil, fmt.Errorf("failed to pack balances(1): %w", err)
	}
	balance1Data, err := client.CallContract(ctx, ethereum.CallMsg{
		To:   &poolAddress,
		Data: balance1Calldata,
	}, nil)
	if err != nil {
		return nil, fmt.Errorf("failed to get balance1: %w", err)
	}
	reserve1 := new(big.Int).SetBytes(balance1Data)

	return &PoolReserves{
		Token0:      token0,
		Token1:      token1,
		Reserve0:    reserve0,
		Reserve1:    reserve1,
		Protocol:    ProtocolCurve,
		PoolAddress: poolAddress,
		Fee:         fee,
		A:           amplificationCoeff,
	}, nil
}

// CalculateOutput calculates expected output for Curve StableSwap
func (d *CurveDecoder) CalculateOutput(amountIn *big.Int, reserves *PoolReserves, tokenIn common.Address) (*big.Int, error) {
	if amountIn == nil || amountIn.Sign() <= 0 {
		return nil, fmt.Errorf("invalid amountIn")
	}

	if reserves.A == nil {
		return nil, fmt.Errorf("missing amplification coefficient A")
	}

	var x, y *big.Int // x = balance of input token, y = balance of output token
	if tokenIn == reserves.Token0 {
		x = reserves.Reserve0
		y = reserves.Reserve1
	} else if tokenIn == reserves.Token1 {
		x = reserves.Reserve1
		y = reserves.Reserve0
	} else {
		return nil, fmt.Errorf("tokenIn not in pool")
	}

	if x.Sign() == 0 || y.Sign() == 0 {
		return nil, fmt.Errorf("insufficient liquidity")
	}

	// Simplified StableSwap calculation
	// Real implementation: y_new = get_y(A, x + dx, D)
	// This is an approximation for demonstration

	// For stable pairs, use near 1:1 pricing with low slippage
	amountOut := new(big.Int).Set(amountIn)

	// Apply fee (0.04% = 9996/10000)
	fee := reserves.Fee
	if fee == nil {
		fee = big.NewInt(4) // 0.04%
	}

	feeBasisPoints := new(big.Int).Sub(big.NewInt(10000), fee)
	amountOut.Mul(amountOut, feeBasisPoints)
	amountOut.Div(amountOut, big.NewInt(10000))

	// For production: Implement full StableSwap invariant D calculation
	// D = A * n^n * sum(x_i) + D = A * n^n * D + D^(n+1) / (n^n * prod(x_i))
	// Then solve for y given new x

	return amountOut, nil
}

// CalculatePriceImpact calculates price impact for Curve
func (d *CurveDecoder) CalculatePriceImpact(amountIn *big.Int, reserves *PoolReserves, tokenIn common.Address) (float64, error) {
	// Curve StableSwap has very low price impact for stable pairs
	// Price impact increases with distance from balance point

	if amountIn == nil || amountIn.Sign() <= 0 {
		return 0, nil
	}

	var x *big.Int
	if tokenIn == reserves.Token0 {
		x = reserves.Reserve0
	} else {
		x = reserves.Reserve1
	}

	if x.Sign() == 0 {
		return 1.0, nil
	}

	// Simple approximation: impact proportional to (amountIn / reserve)^2
	// StableSwap has lower impact than constant product
	amountInFloat := new(big.Float).SetInt(amountIn)
	reserveFloat := new(big.Float).SetInt(x)

	ratio := new(big.Float).Quo(amountInFloat, reserveFloat)
	impact := new(big.Float).Mul(ratio, ratio) // Square for stable curves
	impact.Mul(impact, big.NewFloat(0.1))      // Scale down for StableSwap efficiency

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

// GetQuote gets a price quote for Curve
func (d *CurveDecoder) GetQuote(ctx context.Context, client *ethclient.Client, tokenIn, tokenOut common.Address, amountIn *big.Int) (*PriceQuote, error) {
	// TODO: Implement pool lookup via Curve registry
	// For now, return error
	return nil, fmt.Errorf("GetQuote not yet implemented for Curve")
}

// IsValidPool checks if a pool is a valid Curve pool
func (d *CurveDecoder) IsValidPool(ctx context.Context, client *ethclient.Client, poolAddress common.Address) (bool, error) {
	// Try to call A() - if it succeeds, it's likely a Curve pool
	_, err := client.CallContract(ctx, ethereum.CallMsg{
		To:   &poolAddress,
		Data: d.poolABI.Methods["A"].ID,
	}, nil)

	return err == nil, nil
}