package execution

import (
	"context"
	"fmt"
	"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/ethclient"

	"coppertone.tech/fraktal/mev-bot/pkg/arbitrage"
	"coppertone.tech/fraktal/mev-bot/pkg/observability"
)

// Aave V3 Pool address on Arbitrum
var AaveV3PoolArbitrum = common.HexToAddress("0x794a61358D6845594F94dc1DB02A252b5b4814aD")

// FlashLoanExecutor executes arbitrage opportunities using Aave V3 flash loans
// This allows executing trades with ZERO capital requirement
type FlashLoanExecutor struct {
	client       *ethclient.Client
	logger       observability.Logger
	aavePool     common.Address
	executor     *bind.TransactOpts // Transaction signer
	gasLimit     uint64
	maxGasPrice  *big.Int

	// Stats
	executedCount uint64
	profitTotal   *big.Int
}

// Config for flash loan executor
type Config struct {
	AavePoolAddress common.Address
	GasLimit        uint64
	MaxGasPrice     *big.Int // Maximum gas price willing to pay (in wei)
}

// DefaultConfig returns sensible defaults for Arbitrum
func DefaultConfig() Config {
	return Config{
		AavePoolAddress: AaveV3PoolArbitrum,
		GasLimit:        500000, // 500k gas limit for flash loan + swaps
		MaxGasPrice:     big.NewInt(1e9), // 1 gwei max (Arbitrum is cheap)
	}
}

// NewFlashLoanExecutor creates a new flash loan executor
func NewFlashLoanExecutor(
	client *ethclient.Client,
	executor *bind.TransactOpts,
	logger observability.Logger,
	cfg Config,
) (*FlashLoanExecutor, error) {
	if client == nil {
		return nil, fmt.Errorf("client cannot be nil")
	}
	if executor == nil {
		return nil, fmt.Errorf("executor (transaction signer) cannot be nil")
	}
	if logger == nil {
		return nil, fmt.Errorf("logger cannot be nil")
	}

	return &FlashLoanExecutor{
		client:       client,
		logger:       logger,
		aavePool:     cfg.AavePoolAddress,
		executor:     executor,
		gasLimit:     cfg.GasLimit,
		maxGasPrice:  cfg.MaxGasPrice,
		executedCount: 0,
		profitTotal:   big.NewInt(0),
	}, nil
}

// Execute executes an arbitrage opportunity using a flash loan
// Process:
// 1. Flash loan the input token amount from Aave
// 2. Swap through the arbitrage path (pool1 -> pool2)
// 3. Repay the flash loan + fee
// 4. Keep the profit
func (e *FlashLoanExecutor) Execute(ctx context.Context, opp *arbitrage.Opportunity) (*types.Transaction, error) {
	e.logger.Info("executing arbitrage via flash loan",
		"inputToken", opp.InputToken.Hex(),
		"bridgeToken", opp.BridgeToken.Hex(),
		"inputAmount", opp.InputAmount.String(),
		"profitBPS", opp.ProfitBPS.String(),
	)

	// Check gas price before executing
	gasPrice, err := e.client.SuggestGasPrice(ctx)
	if err != nil {
		return nil, fmt.Errorf("failed to get gas price: %w", err)
	}

	if gasPrice.Cmp(e.maxGasPrice) > 0 {
		return nil, fmt.Errorf("gas price too high: %s > %s", gasPrice.String(), e.maxGasPrice.String())
	}

	// Calculate flash loan fee (Aave V3 charges 0.05% = 5 BPS)
	flashLoanFee := new(big.Int).Mul(opp.InputAmount, big.NewInt(5))
	flashLoanFee.Div(flashLoanFee, big.NewInt(10000))

	// Check if profit covers flash loan fee
	netProfit := new(big.Int).Sub(opp.ProfitAmount, flashLoanFee)
	if netProfit.Cmp(big.NewInt(0)) <= 0 {
		return nil, fmt.Errorf("profit does not cover flash loan fee: profit=%s, fee=%s",
			opp.ProfitAmount.String(), flashLoanFee.String())
	}

	e.logger.Info("flash loan profitability check",
		"grossProfit", opp.ProfitAmount.String(),
		"flashLoanFee", flashLoanFee.String(),
		"netProfit", netProfit.String(),
	)

	// For MVP: Return simulation result (actual execution requires deployed contract)
	// TODO: Deploy flash loan contract and call executeFlashLoan()
	e.logger.Warn("flash loan execution not yet implemented - returning simulation",
		"netProfit", netProfit.String(),
	)

	// Update stats (for simulation)
	e.executedCount++
	e.profitTotal.Add(e.profitTotal, netProfit)

	return nil, fmt.Errorf("flash loan execution not yet implemented - contract deployment needed")
}

// SimulateExecution simulates execution without sending transaction
// Useful for testing profitability before deploying contracts
func (e *FlashLoanExecutor) SimulateExecution(opp *arbitrage.Opportunity) (*SimulationResult, error) {
	// Calculate flash loan fee (Aave V3: 0.05%)
	flashLoanFee := new(big.Int).Mul(opp.InputAmount, big.NewInt(5))
	flashLoanFee.Div(flashLoanFee, big.NewInt(10000))

	// Calculate net profit after flash loan fee
	netProfit := new(big.Int).Sub(opp.ProfitAmount, flashLoanFee)

	// Estimate gas cost
	estimatedGas := new(big.Int).Mul(big.NewInt(int64(e.gasLimit)), e.maxGasPrice)

	// Calculate final profit after gas
	finalProfit := new(big.Int).Sub(netProfit, estimatedGas)

	isProfitable := finalProfit.Cmp(big.NewInt(0)) > 0

	return &SimulationResult{
		GrossProfit:   opp.ProfitAmount,
		FlashLoanFee:  flashLoanFee,
		NetProfit:     netProfit,
		EstimatedGas:  estimatedGas,
		FinalProfit:   finalProfit,
		IsProfitable:  isProfitable,
	}, nil
}

// SimulationResult contains the results of a simulated execution
type SimulationResult struct {
	GrossProfit   *big.Int // Profit before fees
	FlashLoanFee  *big.Int // Aave flash loan fee (0.05%)
	NetProfit     *big.Int // Profit after flash loan fee
	EstimatedGas  *big.Int // Estimated gas cost in wei
	FinalProfit   *big.Int // Final profit after all costs
	IsProfitable  bool     // Whether execution is profitable
}

// GetStats returns execution statistics
func (e *FlashLoanExecutor) GetStats() (executedCount uint64, totalProfit *big.Int) {
	return e.executedCount, new(big.Int).Set(e.profitTotal)
}

// NOTE: Flash loan contract implementation needed
// Contract should implement:
// 1. Aave V3 IFlashLoanSimpleReceiver interface
// 2. executeOperation() callback that:
//    - Swaps token A -> B on pool1
//    - Swaps token B -> A on pool2
//    - Returns borrowed amount + fee to Aave
//    - Transfers profit to owner
//
// Deploy contract code (Solidity):
//
// pragma solidity ^0.8.0;
//
// import "@aave/core-v3/contracts/flashloan/base/FlashLoanSimpleReceiverBase.sol";
// import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
// import "@uniswap/v2-periphery/contracts/interfaces/IUniswapV2Router02.sol";
//
// contract ArbitrageExecutor is FlashLoanSimpleReceiverBase {
//     address public owner;
//
//     constructor(address _addressProvider) FlashLoanSimpleReceiverBase(_addressProvider) {
//         owner = msg.sender;
//     }
//
//     function executeArbitrage(
//         address asset,
//         uint256 amount,
//         address router1,
//         address router2,
//         address[] calldata path1,
//         address[] calldata path2
//     ) external onlyOwner {
//         bytes memory params = abi.encode(router1, router2, path1, path2);
//         POOL.flashLoanSimple(address(this), asset, amount, params, 0);
//     }
//
//     function executeOperation(
//         address asset,
//         uint256 amount,
//         uint256 premium,
//         address initiator,
//         bytes calldata params
//     ) external override returns (bool) {
//         // Decode parameters
//         (address router1, address router2, address[] memory path1, address[] memory path2) =
//             abi.decode(params, (address, address, address[], address[]));
//
//         // Approve routers
//         IERC20(asset).approve(router1, amount);
//
//         // Execute first swap
//         uint[] memory amounts1 = IUniswapV2Router02(router1).swapExactTokensForTokens(
//             amount,
//             0, // No minimum for testing (add slippage protection in production!)
//             path1,
//             address(this),
//             block.timestamp
//         );
//
//         // Approve second router
//         IERC20(path1[path1.length - 1]).approve(router2, amounts1[amounts1.length - 1]);
//
//         // Execute second swap
//         IUniswapV2Router02(router2).swapExactTokensForTokens(
//             amounts1[amounts1.length - 1],
//             amount + premium, // Must get back at least borrowed + fee
//             path2,
//             address(this),
//             block.timestamp
//         );
//
//         // Approve Aave to take back borrowed amount + fee
//         uint256 amountOwed = amount + premium;
//         IERC20(asset).approve(address(POOL), amountOwed);
//
//         // Transfer profit to owner
//         uint256 profit = IERC20(asset).balanceOf(address(this)) - amountOwed;
//         if (profit > 0) {
//             IERC20(asset).transfer(owner, profit);
//         }
//
//         return true;
//     }
//
//     modifier onlyOwner() {
//         require(msg.sender == owner, "Only owner");
//         _;
//     }
// }