package internal

import (
	"context"
	"encoding/json"
	"fmt"
	"math/big"
	"os"
	"path/filepath"
	"time"

	"github.com/fraktal/mev-beta/pkg/math"
)

// GasAuditConfig holds configuration for gas auditing
type GasAuditConfig struct {
	Network       string
	GasPrice      string
	ScenariosFile string
	OutputDir     string
	Verbose       bool
	Tolerance     float64 // Percentage tolerance for gas estimation accuracy
}

// GasAuditor audits gas cost estimations and optimizations
type GasAuditor struct {
	config    *GasAuditConfig
	converter *math.DecimalConverter
	scenarios *GasScenarios
	results   *GasAuditResults
}

// GasScenarios defines test scenarios for gas estimation
type GasScenarios struct {
	Version   string                  `json:"version"`
	Network   string                  `json:"network"`
	Scenarios map[string]*GasScenario `json:"scenarios"`
}

// GasScenario represents a gas estimation test case
type GasScenario struct {
	Name            string `json:"name"`
	Description     string `json:"description"`
	Operation       string `json:"operation"` // "swap", "arbitrage", "flashloan"
	Exchange        string `json:"exchange"`
	TokenIn         string `json:"token_in"`
	TokenOut        string `json:"token_out"`
	AmountIn        string `json:"amount_in"`
	ExpectedGasUsed int64  `json:"expected_gas_used"`
	MaxGasPrice     string `json:"max_gas_price"`
	Priority        string `json:"priority"`   // "low", "medium", "high"
	Complexity      string `json:"complexity"` // "simple", "medium", "complex"
}

// GasAuditResults holds comprehensive gas audit results
type GasAuditResults struct {
	Network            string                  `json:"network"`
	Timestamp          time.Time               `json:"timestamp"`
	TotalScenarios     int                     `json:"total_scenarios"`
	PassedScenarios    int                     `json:"passed_scenarios"`
	FailedScenarios    int                     `json:"failed_scenarios"`
	AverageGasUsed     int64                   `json:"average_gas_used"`
	AverageGasPrice    string                  `json:"average_gas_price"`
	TotalGasCostETH    string                  `json:"total_gas_cost_eth"`
	EstimationAccuracy float64                 `json:"estimation_accuracy"`
	ScenarioResults    []*GasScenarioResult    `json:"scenario_results"`
	FailedCases        []*GasEstimationFailure `json:"failed_cases"`
	Recommendations    []string                `json:"recommendations"`
	Duration           time.Duration           `json:"duration"`
}

// GasScenarioResult represents the result of a gas estimation test
type GasScenarioResult struct {
	ScenarioName            string        `json:"scenario_name"`
	Passed                  bool          `json:"passed"`
	EstimatedGas            int64         `json:"estimated_gas"`
	ActualGas               int64         `json:"actual_gas"`
	EstimationError         float64       `json:"estimation_error_percent"`
	GasPriceGwei            string        `json:"gas_price_gwei"`
	GasCostETH              string        `json:"gas_cost_eth"`
	OptimizationSuggestions []string      `json:"optimization_suggestions"`
	Duration                time.Duration `json:"duration"`
	ErrorMessage            string        `json:"error_message,omitempty"`
}

// GasEstimationFailure represents a failed gas estimation
type GasEstimationFailure struct {
	ScenarioName string  `json:"scenario_name"`
	Reason       string  `json:"reason"`
	ExpectedGas  int64   `json:"expected_gas"`
	EstimatedGas int64   `json:"estimated_gas"`
	ErrorPercent float64 `json:"error_percent"`
	Severity     string  `json:"severity"`
	Impact       string  `json:"impact"`
}

// NewGasAuditor creates a new gas auditor
func NewGasAuditor(config *GasAuditConfig) (*GasAuditor, error) {
	converter := math.NewDecimalConverter()

	// Load gas scenarios
	scenarios, err := loadGasScenarios(config.ScenariosFile, config.Network)
	if err != nil {
		return nil, fmt.Errorf("failed to load gas scenarios: %w", err)
	}

	return &GasAuditor{
		config:    config,
		converter: converter,
		scenarios: scenarios,
		results: &GasAuditResults{
			Network:         config.Network,
			ScenarioResults: []*GasScenarioResult{},
			FailedCases:     []*GasEstimationFailure{},
			Recommendations: []string{},
		},
	}, nil
}

// AuditGasCosts performs comprehensive gas cost auditing
func (ga *GasAuditor) AuditGasCosts(ctx context.Context) error {
	startTime := time.Now()
	ga.results.Timestamp = startTime

	if ga.config.Verbose {
		fmt.Printf("Starting gas cost audit for %s network...\n", ga.config.Network)
	}

	ga.results.TotalScenarios = len(ga.scenarios.Scenarios)
	var totalGasUsed int64
	var totalGasCostETH *math.UniversalDecimal

	// Initialize total gas cost
	totalGasCostETH, _ = math.NewUniversalDecimal(big.NewInt(0), 18, "ETH")

	for name, scenario := range ga.scenarios.Scenarios {
		result, err := ga.runGasScenario(ctx, name, scenario)
		if err != nil {
			if ga.config.Verbose {
				fmt.Printf("  Failed scenario %s: %v\n", name, err)
			}

			failure := &GasEstimationFailure{
				ScenarioName: name,
				Reason:       err.Error(),
				ExpectedGas:  scenario.ExpectedGasUsed,
				Severity:     "high",
				Impact:       "Gas estimation unreliable",
			}
			ga.results.FailedCases = append(ga.results.FailedCases, failure)
			ga.results.FailedScenarios++
			continue
		}

		ga.results.ScenarioResults = append(ga.results.ScenarioResults, result)

		if result.Passed {
			ga.results.PassedScenarios++
			totalGasUsed += result.EstimatedGas

			// Add to total gas cost
			scenarioGasCost, _ := ga.converter.FromString(result.GasCostETH, 18, "ETH")
			totalGasCostETH, _ = ga.converter.Add(totalGasCostETH, scenarioGasCost)
		} else {
			ga.results.FailedScenarios++

			failure := &GasEstimationFailure{
				ScenarioName: name,
				Reason:       result.ErrorMessage,
				ExpectedGas:  scenario.ExpectedGasUsed,
				EstimatedGas: result.EstimatedGas,
				ErrorPercent: result.EstimationError,
				Severity:     ga.calculateGasSeverity(result.EstimationError),
				Impact:       ga.calculateGasImpact(result.EstimationError),
			}
			ga.results.FailedCases = append(ga.results.FailedCases, failure)
		}

		if ga.config.Verbose {
			status := "✓"
			if !result.Passed {
				status = "✗"
			}
			fmt.Printf("  %s %s: Gas=%d, Cost=%s ETH, Error=%.1f%%\n",
				status, name, result.EstimatedGas, result.GasCostETH, result.EstimationError)
		}
	}

	// Calculate summary statistics
	if ga.results.PassedScenarios > 0 {
		ga.results.AverageGasUsed = totalGasUsed / int64(ga.results.PassedScenarios)
		ga.results.EstimationAccuracy = float64(ga.results.PassedScenarios) / float64(ga.results.TotalScenarios) * 100
	}

	ga.results.TotalGasCostETH = ga.converter.ToHumanReadable(totalGasCostETH)
	ga.results.Duration = time.Since(startTime)

	// Generate recommendations
	ga.generateRecommendations()

	if ga.config.Verbose {
		fmt.Printf("Gas audit completed: %d/%d scenarios passed (%.1f%% accuracy)\n",
			ga.results.PassedScenarios, ga.results.TotalScenarios, ga.results.EstimationAccuracy)
	}

	return nil
}

// runGasScenario executes a single gas estimation scenario
func (ga *GasAuditor) runGasScenario(ctx context.Context, name string, scenario *GasScenario) (*GasScenarioResult, error) {
	startTime := time.Now()

	// Simulate gas estimation based on operation complexity
	estimatedGas, err := ga.estimateGasForScenario(scenario)
	if err != nil {
		return nil, fmt.Errorf("gas estimation failed: %w", err)
	}

	// Get current gas price
	gasPrice, err := ga.getCurrentGasPrice()
	if err != nil {
		return nil, fmt.Errorf("failed to get gas price: %w", err)
	}

	// Calculate gas cost in ETH
	gasCostWei := new(big.Int).Mul(big.NewInt(estimatedGas), gasPrice)
	gasCostETH, err := math.NewUniversalDecimal(gasCostWei, 18, "ETH")
	if err != nil {
		return nil, fmt.Errorf("failed to calculate gas cost: %w", err)
	}

	// Calculate estimation error
	estimationError := ga.calculateEstimationError(scenario.ExpectedGasUsed, estimatedGas)

	// Determine if estimation is within tolerance
	passed := estimationError <= ga.config.Tolerance

	// Generate optimization suggestions
	optimizations := ga.generateOptimizationSuggestions(scenario, estimatedGas)

	result := &GasScenarioResult{
		ScenarioName:            name,
		Passed:                  passed,
		EstimatedGas:            estimatedGas,
		ActualGas:               scenario.ExpectedGasUsed,
		EstimationError:         estimationError,
		GasPriceGwei:            ga.weiToGwei(gasPrice),
		GasCostETH:              ga.converter.ToHumanReadable(gasCostETH),
		OptimizationSuggestions: optimizations,
		Duration:                time.Since(startTime),
	}

	if !passed {
		result.ErrorMessage = fmt.Sprintf("Gas estimation error %.1f%% exceeds tolerance %.1f%%",
			estimationError, ga.config.Tolerance)
	}

	return result, nil
}

// estimateGasForScenario estimates gas for a specific scenario
func (ga *GasAuditor) estimateGasForScenario(scenario *GasScenario) (int64, error) {
	// Base gas costs for different operations
	baseGas := map[string]int64{
		"swap":      150000,
		"arbitrage": 300000,
		"flashloan": 500000,
	}

	// Complexity multipliers
	complexityMultiplier := map[string]float64{
		"simple":  1.0,
		"medium":  1.3,
		"complex": 1.8,
	}

	// Exchange-specific adjustments
	exchangeAdjustment := map[string]float64{
		"uniswap_v2": 1.0,
		"uniswap_v3": 1.2,
		"curve":      0.8,
		"balancer":   1.5,
	}

	base, exists := baseGas[scenario.Operation]
	if !exists {
		return 0, fmt.Errorf("unknown operation: %s", scenario.Operation)
	}

	complexityMult, exists := complexityMultiplier[scenario.Complexity]
	if !exists {
		complexityMult = 1.0
	}

	exchangeMult, exists := exchangeAdjustment[scenario.Exchange]
	if !exists {
		exchangeMult = 1.0
	}

	// Calculate estimated gas
	estimated := float64(base) * complexityMult * exchangeMult

	// Add some random variation to simulate real-world conditions
	variation := 0.9 + (0.2 * 0.5) // ±10% variation
	estimated *= variation

	return int64(estimated), nil
}

// getCurrentGasPrice returns current gas price for the network
func (ga *GasAuditor) getCurrentGasPrice() (*big.Int, error) {
	// Simulate gas price based on network
	var gasPriceGwei int64

	switch ga.config.Network {
	case "arbitrum":
		gasPriceGwei = 1 // Arbitrum typically has very low gas prices
	case "ethereum":
		gasPriceGwei = 20 // Ethereum mainnet
	default:
		gasPriceGwei = 10 // Default
	}

	// Convert gwei to wei
	gweiToWei := new(big.Int).Exp(big.NewInt(10), big.NewInt(9), nil)
	gasPrice := new(big.Int).Mul(big.NewInt(gasPriceGwei), gweiToWei)

	return gasPrice, nil
}

// calculateEstimationError calculates the percentage error in gas estimation
func (ga *GasAuditor) calculateEstimationError(expected, estimated int64) float64 {
	if expected == 0 {
		return 0.0
	}

	diff := float64(estimated - expected)
	if diff < 0 {
		diff = -diff
	}

	return (diff / float64(expected)) * 100.0
}

// generateOptimizationSuggestions generates gas optimization suggestions
func (ga *GasAuditor) generateOptimizationSuggestions(scenario *GasScenario, estimatedGas int64) []string {
	var suggestions []string

	// High gas usage suggestions
	if estimatedGas > 400000 {
		suggestions = append(suggestions, "Consider breaking complex operations into smaller transactions")
		suggestions = append(suggestions, "Evaluate if flash loans are necessary for this operation")
	}

	// Exchange-specific suggestions
	switch scenario.Exchange {
	case "uniswap_v3":
		suggestions = append(suggestions, "Consider using single-hop swaps when possible")
	case "balancer":
		suggestions = append(suggestions, "Batch multiple operations to amortize gas costs")
	case "curve":
		suggestions = append(suggestions, "Leverage Curve's low slippage for stable swaps")
	}

	// Operation-specific suggestions
	switch scenario.Operation {
	case "arbitrage":
		suggestions = append(suggestions, "Use multicall to bundle swap operations")
		suggestions = append(suggestions, "Consider gas price optimization strategies")
	case "flashloan":
		suggestions = append(suggestions, "Minimize logic in flash loan callback")
	}

	return suggestions
}

// calculateGasSeverity determines severity of gas estimation error
func (ga *GasAuditor) calculateGasSeverity(errorPercent float64) string {
	switch {
	case errorPercent > 50:
		return "critical"
	case errorPercent > 30:
		return "high"
	case errorPercent > 15:
		return "medium"
	default:
		return "low"
	}
}

// calculateGasImpact determines impact of gas estimation error
func (ga *GasAuditor) calculateGasImpact(errorPercent float64) string {
	switch {
	case errorPercent > 50:
		return "Severe profit impact, transactions may fail"
	case errorPercent > 30:
		return "Significant profit reduction"
	case errorPercent > 15:
		return "Moderate profit impact"
	default:
		return "Minimal impact on profitability"
	}
}

// generateRecommendations generates overall audit recommendations
func (ga *GasAuditor) generateRecommendations() {
	if ga.results.EstimationAccuracy < 80 {
		ga.results.Recommendations = append(ga.results.Recommendations,
			"Gas estimation accuracy is below 80%. Consider improving estimation algorithms.")
	}

	if ga.results.AverageGasUsed > 300000 {
		ga.results.Recommendations = append(ga.results.Recommendations,
			"Average gas usage is high. Consider optimizing transaction complexity.")
	}

	if ga.results.FailedScenarios > ga.results.TotalScenarios/4 {
		ga.results.Recommendations = append(ga.results.Recommendations,
			"High failure rate detected. Review gas estimation methodology.")
	}

	if ga.config.Network == "ethereum" {
		ga.results.Recommendations = append(ga.results.Recommendations,
			"Consider implementing EIP-1559 gas price optimization for Ethereum mainnet.")
	}
}

// MonitorRealTimeGas monitors real-time gas costs and variations
func (ga *GasAuditor) MonitorRealTimeGas(ctx context.Context) error {
	ticker := time.NewTicker(30 * time.Second)
	defer ticker.Stop()

	fmt.Printf("Monitoring real-time gas costs for %s...\n", ga.config.Network)

	for {
		select {
		case <-ctx.Done():
			return ctx.Err()
		case <-ticker.C:
			gasPrice, err := ga.getCurrentGasPrice()
			if err != nil {
				if ga.config.Verbose {
					fmt.Printf("Error getting gas price: %v\n", err)
				}
				continue
			}

			if ga.config.Verbose {
				fmt.Printf("[%s] Current gas price: %s gwei\n",
					time.Now().Format("15:04:05"), ga.weiToGwei(gasPrice))
			}
		}
	}
}

// GenerateReport generates comprehensive gas audit reports
func (ga *GasAuditor) GenerateReport() error {
	// Generate JSON report
	jsonPath := filepath.Join(ga.config.OutputDir, "gas_audit.json")
	if err := ga.generateJSONReport(jsonPath); err != nil {
		return fmt.Errorf("failed to generate JSON report: %w", err)
	}

	// Generate Markdown report
	markdownPath := filepath.Join(ga.config.OutputDir, "gas_audit.md")
	if err := ga.generateMarkdownReport(markdownPath); err != nil {
		return fmt.Errorf("failed to generate Markdown report: %w", err)
	}

	return nil
}

// generateJSONReport generates JSON format report
func (ga *GasAuditor) generateJSONReport(path string) error {
	data, err := json.MarshalIndent(ga.results, "", "  ")
	if err != nil {
		return err
	}

	return os.WriteFile(path, data, 0644)
}

// generateMarkdownReport generates Markdown format report
func (ga *GasAuditor) generateMarkdownReport(path string) error {
	content := fmt.Sprintf("# Gas Cost Audit Report\n\n")
	content += fmt.Sprintf("**Network:** %s\n", ga.results.Network)
	content += fmt.Sprintf("**Generated:** %s\n\n", ga.results.Timestamp.Format(time.RFC3339))

	content += fmt.Sprintf("## Summary\n\n")
	content += fmt.Sprintf("- Total Scenarios: %d\n", ga.results.TotalScenarios)
	content += fmt.Sprintf("- Passed: %d\n", ga.results.PassedScenarios)
	content += fmt.Sprintf("- Failed: %d\n", ga.results.FailedScenarios)
	content += fmt.Sprintf("- Estimation Accuracy: %.1f%%\n", ga.results.EstimationAccuracy)
	content += fmt.Sprintf("- Average Gas Used: %d\n", ga.results.AverageGasUsed)
	content += fmt.Sprintf("- Total Gas Cost: %s ETH\n\n", ga.results.TotalGasCostETH)

	if len(ga.results.Recommendations) > 0 {
		content += fmt.Sprintf("## Recommendations\n\n")
		for _, rec := range ga.results.Recommendations {
			content += fmt.Sprintf("- %s\n", rec)
		}
		content += "\n"
	}

	return os.WriteFile(path, []byte(content), 0644)
}

// weiToGwei converts wei to gwei for display
func (ga *GasAuditor) weiToGwei(wei *big.Int) string {
	gwei := new(big.Int).Div(wei, big.NewInt(1000000000))
	return gwei.String()
}

// loadGasScenarios loads gas estimation scenarios
func loadGasScenarios(filename, network string) (*GasScenarios, error) {
	// Create default scenarios if none specified
	if filename == "default" {
		return createDefaultGasScenarios(network), nil
	}

	// TODO: Load from actual file
	return createDefaultGasScenarios(network), nil
}

// createDefaultGasScenarios creates default gas estimation scenarios
func createDefaultGasScenarios(network string) *GasScenarios {
	scenarios := &GasScenarios{
		Version:   "1.0.0",
		Network:   network,
		Scenarios: make(map[string]*GasScenario),
	}

	// Base scenarios
	scenarios.Scenarios["simple_swap"] = &GasScenario{
		Name:            "simple_swap",
		Description:     "Simple token swap",
		Operation:       "swap",
		Exchange:        "uniswap_v2",
		TokenIn:         "ETH",
		TokenOut:        "USDC",
		AmountIn:        "1000000000000000000",
		ExpectedGasUsed: 150000,
		MaxGasPrice:     "50000000000",
		Priority:        "medium",
		Complexity:      "simple",
	}

	scenarios.Scenarios["complex_arbitrage"] = &GasScenario{
		Name:            "complex_arbitrage",
		Description:     "Multi-hop arbitrage",
		Operation:       "arbitrage",
		Exchange:        "uniswap_v3",
		TokenIn:         "ETH",
		TokenOut:        "USDC",
		AmountIn:        "10000000000000000000",
		ExpectedGasUsed: 400000,
		MaxGasPrice:     "100000000000",
		Priority:        "high",
		Complexity:      "complex",
	}

	scenarios.Scenarios["flashloan_arbitrage"] = &GasScenario{
		Name:            "flashloan_arbitrage",
		Description:     "Flash loan arbitrage",
		Operation:       "flashloan",
		Exchange:        "balancer",
		TokenIn:         "ETH",
		TokenOut:        "USDC",
		AmountIn:        "100000000000000000000",
		ExpectedGasUsed: 600000,
		MaxGasPrice:     "150000000000",
		Priority:        "high",
		Complexity:      "complex",
	}

	return scenarios
}