package execution

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

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/ethclient"

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

// ExecutionMode defines how opportunities should be executed
type ExecutionMode int

const (
	// SimulationMode only simulates execution without sending transactions
	SimulationMode ExecutionMode = iota
	// DryRunMode validates transactions but doesn't send
	DryRunMode
	// LiveMode executes real transactions on-chain
	LiveMode
)

// ExecutionResult represents the result of an arbitrage execution
type ExecutionResult struct {
	OpportunityID   string
	Success         bool
	TxHash          common.Hash
	GasUsed         uint64
	ActualProfit    *big.Int
	EstimatedProfit *big.Int
	SlippagePercent float64
	ExecutionTime   time.Duration
	Error           error
	Timestamp       time.Time
}

// ExecutionConfig holds configuration for the executor
type ExecutionConfig struct {
	Mode               ExecutionMode
	MaxGasPrice        *big.Int // Maximum gas price willing to pay (wei)
	MaxSlippage        float64  // Maximum slippage tolerance (0.05 = 5%)
	MinProfitThreshold *big.Int // Minimum profit to execute (wei)
	SimulationRPCURL   string   // RPC URL for simulation/fork testing
	FlashLoanProvider  string   // "aave", "uniswap", "balancer"
	MaxRetries         int      // Maximum execution retries
	RetryDelay         time.Duration
	EnableParallelExec bool // Execute multiple opportunities in parallel
	DryRun             bool // If true, don't send transactions
}

// ArbitrageExecutor handles execution of arbitrage opportunities
type ArbitrageExecutor struct {
	config      *ExecutionConfig
	client      *ethclient.Client
	logger      *logger.Logger
	flashLoan   FlashLoanProvider
	slippage    *SlippageProtector
	simulator   *ExecutionSimulator
	resultsChan chan *ExecutionResult
	stopChan    chan struct{}
}

// FlashLoanProvider interface for different flash loan protocols
type FlashLoanProvider interface {
	// ExecuteFlashLoan executes an arbitrage opportunity using flash loans
	ExecuteFlashLoan(ctx context.Context, opportunity *types.ArbitrageOpportunity, config *ExecutionConfig) (*ExecutionResult, error)

	// GetMaxLoanAmount returns maximum loan amount available for a token
	GetMaxLoanAmount(ctx context.Context, token common.Address) (*big.Int, error)

	// GetFee returns the flash loan fee for a given amount
	GetFee(ctx context.Context, amount *big.Int) (*big.Int, error)

	// SupportsToken checks if the provider supports a given token
	SupportsToken(token common.Address) bool
}

// SlippageProtector handles slippage protection and validation
type SlippageProtector struct {
	maxSlippage float64
	logger      *logger.Logger
}

// ExecutionSimulator simulates trades on a fork before real execution
type ExecutionSimulator struct {
	forkClient *ethclient.Client
	logger     *logger.Logger
}

// NewArbitrageExecutor creates a new arbitrage executor
func NewArbitrageExecutor(
	config *ExecutionConfig,
	client *ethclient.Client,
	logger *logger.Logger,
) (*ArbitrageExecutor, error) {
	if config == nil {
		return nil, fmt.Errorf("execution config cannot be nil")
	}

	executor := &ArbitrageExecutor{
		config:      config,
		client:      client,
		logger:      logger,
		resultsChan: make(chan *ExecutionResult, 100),
		stopChan:    make(chan struct{}),
	}

	// Initialize slippage protector
	executor.slippage = &SlippageProtector{
		maxSlippage: config.MaxSlippage,
		logger:      logger,
	}

	// Initialize simulator if simulation RPC is provided
	if config.SimulationRPCURL != "" {
		forkClient, err := ethclient.Dial(config.SimulationRPCURL)
		if err != nil {
			logger.Warn(fmt.Sprintf("Failed to connect to simulation RPC: %v", err))
		} else {
			executor.simulator = &ExecutionSimulator{
				forkClient: forkClient,
				logger:     logger,
			}
			logger.Info("Execution simulator initialized")
		}
	}

	// Initialize flash loan provider
	switch config.FlashLoanProvider {
	case "aave":
		executor.flashLoan = NewAaveFlashLoanProvider(client, logger)
		logger.Info("Using Aave flash loans")
	case "uniswap":
		executor.flashLoan = NewUniswapFlashLoanProvider(client, logger)
		logger.Info("Using Uniswap flash swaps")
	case "balancer":
		executor.flashLoan = NewBalancerFlashLoanProvider(client, logger)
		logger.Info("Using Balancer flash loans")
	default:
		logger.Warn(fmt.Sprintf("Unknown flash loan provider: %s, using Aave", config.FlashLoanProvider))
		executor.flashLoan = NewAaveFlashLoanProvider(client, logger)
	}

	return executor, nil
}

// ExecuteOpportunity executes an arbitrage opportunity
func (ae *ArbitrageExecutor) ExecuteOpportunity(ctx context.Context, opportunity *types.ArbitrageOpportunity) (*ExecutionResult, error) {
	startTime := time.Now()

	ae.logger.Info(fmt.Sprintf("🎯 Executing arbitrage opportunity: %s", opportunity.ID))

	// Step 1: Validate opportunity is still profitable
	if !ae.validateOpportunity(opportunity) {
		return &ExecutionResult{
			OpportunityID: opportunity.ID,
			Success:       false,
			Error:         fmt.Errorf("opportunity validation failed"),
			Timestamp:     time.Now(),
		}, nil
	}

	// Step 2: Check slippage limits
	if err := ae.slippage.ValidateSlippage(opportunity); err != nil {
		ae.logger.Warn(fmt.Sprintf("Slippage validation failed: %v", err))
		return &ExecutionResult{
			OpportunityID: opportunity.ID,
			Success:       false,
			Error:         fmt.Errorf("slippage too high: %w", err),
			Timestamp:     time.Now(),
		}, nil
	}

	// Step 3: Simulate execution if simulator available
	if ae.simulator != nil && ae.config.Mode != LiveMode {
		simulationResult, err := ae.simulator.Simulate(ctx, opportunity, ae.config)
		if err != nil {
			ae.logger.Error(fmt.Sprintf("Simulation failed: %v", err))
			return &ExecutionResult{
				OpportunityID: opportunity.ID,
				Success:       false,
				Error:         fmt.Errorf("simulation failed: %w", err),
				Timestamp:     time.Now(),
			}, nil
		}

		// If in simulation mode, return simulation result
		if ae.config.Mode == SimulationMode {
			simulationResult.ExecutionTime = time.Since(startTime)
			return simulationResult, nil
		}

		ae.logger.Info(fmt.Sprintf("Simulation succeeded: profit=%s ETH", simulationResult.ActualProfit.String()))
	}

	// Step 4: Execute via flash loan (if not in dry-run mode)
	if ae.config.DryRun || ae.config.Mode == DryRunMode {
		ae.logger.Info("Dry-run mode: skipping real execution")
		return &ExecutionResult{
			OpportunityID:   opportunity.ID,
			Success:         true,
			EstimatedProfit: opportunity.NetProfit,
			Error:           nil,
			ExecutionTime:   time.Since(startTime),
			Timestamp:       time.Now(),
		}, nil
	}

	// Step 5: Real execution
	result, err := ae.flashLoan.ExecuteFlashLoan(ctx, opportunity, ae.config)
	if err != nil {
		ae.logger.Error(fmt.Sprintf("Flash loan execution failed: %v", err))
		return &ExecutionResult{
			OpportunityID: opportunity.ID,
			Success:       false,
			Error:         err,
			ExecutionTime: time.Since(startTime),
			Timestamp:     time.Now(),
		}, err
	}

	result.ExecutionTime = time.Since(startTime)
	ae.logger.Info(fmt.Sprintf("✅ Arbitrage executed successfully: profit=%s ETH, gas=%d",
		result.ActualProfit.String(), result.GasUsed))

	// Send result to channel for monitoring
	select {
	case ae.resultsChan <- result:
	default:
		ae.logger.Warn("Results channel full, dropping result")
	}

	return result, nil
}

// validateOpportunity validates that an opportunity is still valid
func (ae *ArbitrageExecutor) validateOpportunity(opp *types.ArbitrageOpportunity) bool {
	// Check minimum profit threshold
	if opp.NetProfit.Cmp(ae.config.MinProfitThreshold) < 0 {
		ae.logger.Debug(fmt.Sprintf("Opportunity below profit threshold: %s < %s",
			opp.NetProfit.String(), ae.config.MinProfitThreshold.String()))
		return false
	}

	// Check opportunity hasn't expired
	if time.Now().After(opp.ExpiresAt) {
		ae.logger.Debug("Opportunity has expired")
		return false
	}

	// Additional validation checks can be added here
	// - Re-fetch pool states
	// - Verify liquidity still available
	// - Check gas prices haven't spiked

	return true
}

// ValidateSlippage checks if slippage is within acceptable limits
func (sp *SlippageProtector) ValidateSlippage(opp *types.ArbitrageOpportunity) error {
	// Calculate expected slippage based on pool liquidity
	// This is a simplified version - production would need more sophisticated calculation

	if opp.PriceImpact > sp.maxSlippage {
		return fmt.Errorf("slippage %.2f%% exceeds maximum %.2f%%",
			opp.PriceImpact*100, sp.maxSlippage*100)
	}

	return nil
}

// Simulate simulates execution on a fork
func (es *ExecutionSimulator) Simulate(
	ctx context.Context,
	opportunity *types.ArbitrageOpportunity,
	config *ExecutionConfig,
) (*ExecutionResult, error) {
	es.logger.Info(fmt.Sprintf("🧪 Simulating arbitrage: %s", opportunity.ID))

	// In a real implementation, this would:
	// 1. Fork the current blockchain state
	// 2. Execute the arbitrage path on the fork
	// 3. Validate results match expectations
	// 4. Return simulated result

	// For now, return a simulated success
	return &ExecutionResult{
		OpportunityID:   opportunity.ID,
		Success:         true,
		ActualProfit:    opportunity.NetProfit,
		EstimatedProfit: opportunity.NetProfit,
		SlippagePercent: 0.01, // 1% simulated slippage
		Timestamp:       time.Now(),
	}, nil
}

// GetResultsChannel returns the channel for execution results
func (ae *ArbitrageExecutor) GetResultsChannel() <-chan *ExecutionResult {
	return ae.resultsChan
}

// Stop stops the executor
func (ae *ArbitrageExecutor) Stop() {
	close(ae.stopChan)
	ae.logger.Info("Arbitrage executor stopped")
}