# Flash Loan Execution - Deployment & Integration Guide

**Status:** Framework Complete, Contracts Ready for Deployment

**Last Updated:** October 26, 2025

---

## 📋 Overview

This guide covers the deployment and integration of the MEV bot's flash loan execution system, which enables real arbitrage execution using flash loans from multiple providers.

### Architecture Summary

```
┌─────────────────────────────────────────────────────────────┐
│                      MEV Bot Go Process                      │
│                                                              │
│  ┌────────────────┐         ┌──────────────────┐           │
│  │   Arbitrage    │────────▶│  Flash Loan      │           │
│  │   Detector     │         │  Provider        │           │
│  └────────────────┘         └────────┬─────────┘           │
│                                      │                       │
└──────────────────────────────────────┼───────────────────────┘
                                       │ RPC Call
                                       ▼
                    ┌──────────────────────────────────┐
                    │   FlashLoanReceiver Contract     │
                    │   (Deployed on Arbitrum)        │
                    └────────┬─────────────────────────┘
                             │
         ┌───────────────────┼──────────────────────┐
         │                   │                      │
         ▼                   ▼                      ▼
   ┌─────────────┐   ┌──────────────┐   ┌──────────────────┐
   │  Balancer   │   │  Uniswap V2  │   │  Uniswap V3      │
   │  Vault      │   │  Router      │   │  Router          │
   │  (0% fee)   │   │  (0.3% fee)  │   │  (0.05%-1% fee)  │
   └─────────────┘   └──────────────┘   └──────────────────┘
```

---

## 🎯 Implementation Status

### ✅ Complete

1. **Solidity Smart Contract**
   - Location: `contracts/balancer/FlashLoanReceiver.sol`
   - Features:
     - Balancer flash loan integration
     - Uniswap V2/V3 swap execution
     - Profit calculation and validation
     - Owner-only access control
     - Emergency withdrawal

2. **Go Execution Framework**
   - Location: `pkg/execution/`
   - Files:
     - `executor.go` - Core execution engine (316 lines)
     - `flashloan_providers.go` - Provider implementations (360+ lines)
     - `alerts.go` - Alert system (291 lines)

3. **ABI Bindings**
   - Location: `bindings/balancer/vault.go`
   - Generated with abigen for Balancer Vault

4. **Calldata Encoding**
   - Function: `encodeArbitragePath()` in flashloan_providers.go
   - Encodes ArbitragePath struct for contract

### ⏳ Pending

1. **Smart Contract Deployment**
   - Deploy FlashLoanReceiver.sol to Arbitrum
   - Set receiver address in BalancerFlashLoanProvider
   - Fund contract with gas if needed

2. **Transaction Signing**
   - Implement private key management
   - Add transaction signer
   - Gas estimation logic

3. **ABI Encoding/Decoding**
   - Complete ABI encoding for ArbitragePath struct
   - Parse execution results from contract events

4. **Integration Testing**
   - Test on Arbitrum testnet
   - Fork testing with Tenderly/Hardhat
   - Mainnet dry-run testing

---

## 🚀 Deployment Steps

### Prerequisites

```bash
# Install dependencies
npm install --save-dev hardhat @nomiclabs/hardhat-ethers ethers
npm install @openzeppelin/contracts

# Or use Foundry (recommended for production)
curl -L https://foundry.paradigm.xyz | bash
foundryup
```

### Step 1: Compile Contract

**Using Hardhat:**
```bash
npx hardhat compile contracts/balancer/FlashLoanReceiver.sol
```

**Using Foundry:**
```bash
forge build contracts/balancer/FlashLoanReceiver.sol
```

### Step 2: Deploy to Arbitrum

**Deployment Script (Hardhat):**

```javascript
// scripts/deploy-flash-receiver.js
const hre = require("hardhat");

async function main() {
  const BALANCER_VAULT = "0xBA12222222228d8Ba445958a75a0704d566BF2C8";

  console.log("Deploying FlashLoanReceiver...");

  const FlashLoanReceiver = await hre.ethers.getContractFactory("FlashLoanReceiver");
  const receiver = await FlashLoanReceiver.deploy(BALANCER_VAULT);

  await receiver.deployed();

  console.log("✅ FlashLoanReceiver deployed to:", receiver.address);
  console.log("   Owner:", await receiver.owner());
  console.log("   Vault:", await receiver.vault());

  // Save deployment info
  const fs = require("fs");
  fs.writeFileSync("deployment.json", JSON.stringify({
    address: receiver.address,
    owner: await receiver.owner(),
    vault: BALANCER_VAULT,
    timestamp: new Date().toISOString()
  }, null, 2));
}

main()
  .then(() => process.exit(0))
  .catch((error) => {
    console.error(error);
    process.exit(1);
  });
```

**Deploy:**
```bash
npx hardhat run scripts/deploy-flash-receiver.js --network arbitrum
```

**Using Foundry:**
```bash
forge create contracts/balancer/FlashLoanReceiver.sol:FlashLoanReceiver \
  --rpc-url $ARBITRUM_RPC \
  --private-key $PRIVATE_KEY \
  --constructor-args 0xBA12222222228d8Ba445958a75a0704d566BF2C8 \
  --verify
```

### Step 3: Configure MEV Bot

After deployment, update the Go code with the deployed contract address:

```go
// pkg/execution/flashloan_providers.go

func NewBalancerFlashLoanProvider(client *ethclient.Client, logger *logger.Logger) *BalancerFlashLoanProvider {
	return &BalancerFlashLoanProvider{
		client: client,
		logger: logger,
		vaultAddress: common.HexToAddress("0xBA12222222228d8Ba445958a75a0704d566BF2C8"),
		// UPDATE THIS with deployed contract address:
		receiverAddress: common.HexToAddress("0xYOUR_DEPLOYED_CONTRACT_ADDRESS"),
	}
}
```

Or use environment variable:
```bash
export FLASH_LOAN_RECEIVER="0xYOUR_DEPLOYED_CONTRACT_ADDRESS"
```

### Step 4: Generate Contract Bindings

Generate Go bindings for the deployed contract:

```bash
# Get contract ABI
cat contracts/balancer/FlashLoanReceiver.sol | \
  solc --abi - > contracts/balancer/FlashLoanReceiver.abi

# Generate Go bindings
abigen --abi contracts/balancer/FlashLoanReceiver.abi \
  --pkg execution \
  --type FlashLoanReceiver \
  --out pkg/execution/flashloan_receiver.go
```

---

## 🔧 Integration Implementation

### Complete the TODO Items

**1. Transaction Signing (`pkg/execution/transaction_signer.go` - NEW FILE)**

```go
package execution

import (
	"context"
	"crypto/ecdsa"
	"math/big"

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

type TransactionSigner struct {
	privateKey *ecdsa.PrivateKey
	chainID    *big.Int
	client     *ethclient.Client
}

func NewTransactionSigner(privateKeyHex string, client *ethclient.Client) (*TransactionSigner, error) {
	privateKey, err := crypto.HexToECDSA(privateKeyHex)
	if err != nil {
		return nil, err
	}

	chainID, err := client.ChainID(context.Background())
	if err != nil {
		return nil, err
	}

	return &TransactionSigner{
		privateKey: privateKey,
		chainID:    chainID,
		client:     client,
	}, nil
}

func (ts *TransactionSigner) SignAndSend(ctx context.Context, tx *types.Transaction) (common.Hash, error) {
	signedTx, err := types.SignTx(tx, types.NewEIP155Signer(ts.chainID), ts.privateKey)
	if err != nil {
		return common.Hash{}, err
	}

	err = ts.client.SendTransaction(ctx, signedTx)
	if err != nil {
		return common.Hash{}, err
	}

	return signedTx.Hash(), nil
}

func (ts *TransactionSigner) GetTransactor() (*bind.TransactOpts, error) {
	auth, err := bind.NewKeyedTransactorWithChainID(ts.privateKey, ts.chainID)
	if err != nil {
		return nil, err
	}
	return auth, nil
}
```

**2. Complete ABI Encoding**

Update `encodeArbitragePath()` to use proper ABI encoding:

```go
import (
	"github.com/ethereum/go-ethereum/accounts/abi"
	"strings"
)

func (b *BalancerFlashLoanProvider) encodeArbitragePath(
	opportunity *arbitrage.ArbitragePath,
	config *ExecutionConfig,
) ([]byte, error) {
	// Define ABI for ArbitragePath struct
	arbitragePathABI := `[{
		"components": [
			{"name": "tokens", "type": "address[]"},
			{"name": "exchanges", "type": "address[]"},
			{"name": "fees", "type": "uint24[]"},
			{"name": "isV3", "type": "bool[]"},
			{"name": "minProfit", "type": "uint256"}
		],
		"name": "path",
		"type": "tuple"
	}]`

	contractABI, err := abi.JSON(strings.NewReader(arbitragePathABI))
	if err != nil {
		return nil, err
	}

	// Prepare data (same as before)
	numHops := len(opportunity.TokenPath) - 1
	exchanges := make([]common.Address, numHops)
	fees := make([]*big.Int, numHops)
	isV3 := make([]bool, numHops)

	// ... (populate arrays) ...

	// Encode using ABI
	encoded, err := contractABI.Pack("path",
		opportunity.TokenPath,
		exchanges,
		fees,
		isV3,
		minProfit,
	)
	if err != nil {
		return nil, err
	}

	return encoded, nil
}
```

**3. Complete ExecuteFlashLoan**

```go
func (b *BalancerFlashLoanProvider) ExecuteFlashLoan(
	ctx context.Context,
	opportunity *arbitrage.ArbitragePath,
	config *ExecutionConfig,
) (*ExecutionResult, error) {
	startTime := time.Now()

	// ... (validation and encoding as before) ...

	// Create contract instance
	receiver, err := NewFlashLoanReceiver(b.receiverAddress, b.client)
	if err != nil {
		return nil, err
	}

	// Get transactor
	auth, err := config.Signer.GetTransactor()
	if err != nil {
		return nil, err
	}

	// Set gas price and limit
	auth.GasPrice = config.MaxGasPrice
	auth.GasLimit = 500000 // Estimate based on path length

	// Call executeArbitrage
	tx, err := receiver.ExecuteArbitrage(auth, tokens, amounts, userData)
	if err != nil {
		return &ExecutionResult{
			OpportunityID: opportunity.ID,
			Success:       false,
			Error:         err,
			ExecutionTime: time.Since(startTime),
		}, err
	}

	// Wait for receipt
	receipt, err := bind.WaitMined(ctx, b.client, tx)
	if err != nil {
		return &ExecutionResult{
			OpportunityID: opportunity.ID,
			Success:       false,
			TxHash:        tx.Hash(),
			Error:         err,
			ExecutionTime: time.Since(startTime),
		}, err
	}

	// Parse events to get actual profit
	var actualProfit *big.Int
	for _, log := range receipt.Logs {
		event, err := receiver.ParseArbitrageExecuted(*log)
		if err == nil {
			actualProfit = event.Profit
			break
		}
	}

	return &ExecutionResult{
		OpportunityID:   opportunity.ID,
		Success:         receipt.Status == 1,
		TxHash:          tx.Hash(),
		GasUsed:         receipt.GasUsed,
		ActualProfit:    actualProfit,
		EstimatedProfit: opportunity.NetProfit,
		ExecutionTime:   time.Since(startTime),
		Timestamp:       time.Now(),
	}, nil
}
```

---

## ✅ Testing Strategy

### 1. Local Fork Testing

```bash
# Start Hardhat node with Arbitrum fork
npx hardhat node --fork https://arb1.arbitrum.io/rpc

# Deploy contract to local fork
npx hardhat run scripts/deploy-flash-receiver.js --network localhost

# Run Go tests against local fork
export ARBITRUM_RPC_ENDPOINT="http://localhost:8545"
export FLASH_LOAN_RECEIVER="0x..."
go test ./pkg/execution/... -v
```

### 2. Arbitrum Testnet

```bash
# Deploy to Arbitrum Sepolia testnet
npx hardhat run scripts/deploy-flash-receiver.js --network arbitrum-sepolia

# Test with testnet RPC
export ARBITRUM_RPC_ENDPOINT="https://sepolia-rollup.arbitrum.io/rpc"
./mev-bot start --dry-run
```

### 3. Mainnet Dry-Run

```bash
# Test on mainnet without executing
export EXECUTION_MODE="simulation"
./mev-bot start
```

---

## 📊 Gas Optimization

### Estimated Gas Costs

| Operation | Gas Estimate | Cost (@ 0.1 gwei) |
|-----------|-------------|-------------------|
| Contract deployment | 1,500,000 | 0.00015 ETH |
| 2-hop arbitrage | 300,000 | 0.00003 ETH |
| 3-hop arbitrage | 450,000 | 0.000045 ETH |
| 4-hop arbitrage | 600,000 | 0.00006 ETH |

### Optimization Tips

1. **Batch token approvals** - Approve max once instead of per transaction
2. **Use V3 single-hop when possible** - Lower gas than multi-contract calls
3. **Optimize path length** - 2-hop paths preferred
4. **Monitor gas prices** - Only execute when gas < threshold

---

## 🔐 Security Considerations

### Smart Contract Security

1. **Access Control**
   - Only owner can call `executeArbitrage()`
   - Only Balancer Vault can call `receiveFlashLoan()`

2. **Profit Validation**
   - Minimum profit threshold enforced on-chain
   - Prevents unprofitable execution

3. **Emergency Functions**
   - `emergencyWithdraw()` for stuck funds
   - `withdrawProfit()` for profit extraction

### Operational Security

1. **Private Key Management**
   ```bash
   # NEVER commit private keys to git
   # Use environment variables or secret managers
   export EXECUTOR_PRIVATE_KEY="0x..."

   # Or use hardware wallets (Ledger/Trezor)
   # Or use AWS KMS / Google Cloud KMS
   ```

2. **Gas Price Limits**
   ```go
   config := &ExecutionConfig{
       MaxGasPrice: big.NewInt(1000000000), // 1 gwei max
       // ...
   }
   ```

3. **Slippage Protection**
   - Set `MaxSlippage` appropriately
   - Default 5% is reasonable for volatile markets

---

## 📈 Monitoring & Alerts

### Integration with Alert System

```go
// In main.go or orchestrator
alertSystem := execution.NewAlertSystem(&execution.AlertConfig{
    EnableConsoleAlerts: true,
    EnableWebhook:       true,
    WebhookURL:          os.Getenv("SLACK_WEBHOOK"),
    MinProfitForAlert:   big.NewInt(1e16), // 0.01 ETH
    MinROIForAlert:      0.05,              // 5%
}, logger)

// Send execution alerts
result, err := executor.ExecuteOpportunity(ctx, opportunity)
if err == nil {
    alertSystem.SendExecutionAlert(result)
}
```

### Dashboard Metrics

Add to `monitoring/dashboard.sh`:
```bash
# Execution metrics
EXECUTIONS=$(grep -c "Arbitrage executed successfully" "${LATEST_LOG}")
EXECUTION_PROFIT=$(grep "profit=" "${LATEST_LOG}" | awk '{sum+=$NF} END {print sum}')
echo "  Executions: ${EXECUTIONS}"
echo "  Total Profit: ${EXECUTION_PROFIT} ETH"
```

---

## 🎯 Next Steps

1. **Deploy FlashLoanReceiver contract** to Arbitrum
2. **Implement transaction signing** in Go
3. **Complete ABI encoding** for ArbitragePath
4. **Test on Arbitrum testnet**
5. **Conduct security audit** of smart contract
6. **Monitor 24-hour test results** before enabling execution
7. **Start with small amounts** (0.01-0.1 ETH)
8. **Scale gradually** as confidence builds

---

## 📚 Reference

- **Balancer Vault:** 0xBA12222222228d8Ba445958a75a0704d566BF2C8
- **Flash Loan Docs:** https://docs.balancer.fi/reference/contracts/flash-loans.html
- **Arbitrum RPC:** https://docs.arbitrum.io/build-decentralized-apps/reference/node-providers
- **Go-Ethereum Docs:** https://geth.ethereum.org/docs

---

*Last Updated: October 26, 2025*
*Status: Ready for Deployment*