// Package execution implements the execution layer for the MEV bot.
// It manages prioritized execution of arbitrage opportunities with features like
// priority-based queues, circuit breakers, rate limiting, and retry logic.
package execution

import (
	"container/heap"
	"context"
	"errors"
	"fmt"
	"math/big"
	"sync"
	"time"

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

var (
	// ErrQueueFullLowerPriority indicates that the queue is full and the new opportunity has lower priority than existing items
	ErrQueueFullLowerPriority = errors.New("queue full and new opportunity has lower priority")
)

const (
	// Default queue configuration
	DefaultMaxQueueSize  = 100
	DefaultExecutionRate = 500 * time.Millisecond
	DefaultMaxRetries    = 3

	// Circuit breaker configuration
	CircuitBreakerMaxFailures = 5
	CircuitBreakerTimeWindow  = 5 * time.Minute

	// Priority calculation factors
	ProfitScoreScaleFactor   = 10.0
	ConfidenceBoostFactor    = 20.0
	MarginBoostFactor        = 10.0
	DefaultTimeDecayPriority = 100.0

	// Execution simulation parameters
	ConfidenceThresholdForSuccess = 0.7
	SimulatedExecutionTime        = 200 * time.Millisecond
)

// ExecutionQueue manages prioritized execution of arbitrage opportunities
type ExecutionQueue struct {
	logger         *logger.Logger
	queue          *PriorityQueue
	mu             sync.RWMutex
	maxQueueSize   int
	executionRate  time.Duration
	circuitBreaker *CircuitBreaker

	// Execution stats
	totalExecuted  int64
	successCount   int64
	failureCount   int64
	totalProfitUSD float64
}

// ExecutionItem represents an arbitrage opportunity in the execution queue
type ExecutionItem struct {
	Opportunity *pkgtypes.ArbitrageOpportunity
	Priority    float64 // Higher = more urgent
	Timestamp   time.Time
	Retries     int
	MaxRetries  int
}

// PriorityQueue implements a priority queue for execution items
type PriorityQueue []*ExecutionItem

func (pq PriorityQueue) Len() int { return len(pq) }

func (pq PriorityQueue) Less(i, j int) bool {
	// Higher priority first, then by timestamp for tie-breaking
	if pq[i].Priority != pq[j].Priority {
		return pq[i].Priority > pq[j].Priority
	}
	return pq[i].Timestamp.Before(pq[j].Timestamp)
}

func (pq PriorityQueue) Swap(i, j int) {
	pq[i], pq[j] = pq[j], pq[i]
}

func (pq *PriorityQueue) Push(x interface{}) {
	*pq = append(*pq, x.(*ExecutionItem))
}

func (pq *PriorityQueue) Pop() interface{} {
	old := *pq
	n := len(old)
	item := old[n-1]
	*pq = old[0 : n-1]
	return item
}

// CircuitBreaker prevents execution when too many failures occur
type CircuitBreaker struct {
	maxFailures int
	timeWindow  time.Duration
	failures    []time.Time
	isOpen      bool
	mu          sync.RWMutex
}

// NewExecutionQueue creates a new execution queue
func NewExecutionQueue(logger *logger.Logger) *ExecutionQueue {
	pq := &PriorityQueue{}
	heap.Init(pq)

	return &ExecutionQueue{
		logger:        logger,
		queue:         pq,
		maxQueueSize:  DefaultMaxQueueSize,
		executionRate: DefaultExecutionRate, // Execute every 500ms max
		circuitBreaker: &CircuitBreaker{
			maxFailures: CircuitBreakerMaxFailures,
			timeWindow:  CircuitBreakerTimeWindow,
			failures:    make([]time.Time, 0),
		},
	}
}

// AddOpportunity adds an arbitrage opportunity to the execution queue
func (eq *ExecutionQueue) AddOpportunity(opportunity *pkgtypes.ArbitrageOpportunity) error {
	eq.mu.Lock()
	defer eq.mu.Unlock()

	// Check if queue is full
	if eq.queue.Len() >= eq.maxQueueSize {
		// Remove lowest priority item
		if eq.queue.Len() > 0 {
			lowestPriorityItem := (*eq.queue)[eq.queue.Len()-1]
			if eq.calculatePriority(opportunity) > lowestPriorityItem.Priority {
				heap.Pop(eq.queue) // Remove lowest priority
				eq.logger.Info("Queue full, replaced lower priority opportunity")
			} else {
				return ErrQueueFullLowerPriority
			}
		}
	}

	// Create execution item
	item := &ExecutionItem{
		Opportunity: opportunity,
		Priority:    eq.calculatePriority(opportunity),
		Timestamp:   time.Now(),
		MaxRetries:  DefaultMaxRetries,
	}

	heap.Push(eq.queue, item)

	// Convert UniversalDecimal to float64 for display
	profitFloat := 0.0
	if opportunity.NetProfit != nil {
		profitEth := new(big.Float).Quo(new(big.Float).SetInt(opportunity.NetProfit), big.NewFloat(1e18))
		var accuracy big.Accuracy
		profitFloat, accuracy = profitEth.Float64()
		// Check if the conversion was exact (accuracy == 0) or if there was a loss of precision
		if accuracy != big.Exact {
			eq.logger.Warn("NetProfit conversion to float64 may have lost precision, accuracy: %v", accuracy)
		}
	}
	eq.logger.Info(fmt.Sprintf("📋 Added arbitrage opportunity to queue: %.6f ETH profit, priority: %.2f",
		profitFloat, item.Priority))

	return nil
}

// calculatePriority calculates execution priority based on profit, confidence, and time sensitivity
func (eq *ExecutionQueue) calculatePriority(opp *pkgtypes.ArbitrageOpportunity) float64 {
	// Base priority on profit potential
	// Convert NetProfit to float64 for priority calculation
	profitScore := 0.0
	if opp.NetProfit != nil {
		profitEth := new(big.Float).Quo(new(big.Float).SetInt(opp.NetProfit), big.NewFloat(1e18))
		var accuracy big.Accuracy
		profitScore, accuracy = profitEth.Float64()
		// Check if the conversion was exact (accuracy == 0) or if there was a loss of precision
		if accuracy != big.Exact {
			eq.logger.Warn("NetProfit conversion to float64 may have lost precision, accuracy: %v", accuracy)
		}
		profitScore *= ProfitScoreScaleFactor // Scale by factor
	}

	// Boost for high confidence
	confidenceBoost := opp.Confidence * ConfidenceBoostFactor

	// Boost for large profit margins (indicates stable opportunity)
	marginBoost := opp.ROI * MarginBoostFactor // ROI is already a float64 percentage

	// Time decay - use current time as opportunities don't have timestamps
	// This could be enhanced by adding creation timestamp to ArbitrageOpportunity
	timeDecay := DefaultTimeDecayPriority // Default high priority for new opportunities

	priority := profitScore + confidenceBoost + marginBoost + timeDecay

	return priority
}

// Start begins processing the execution queue
func (eq *ExecutionQueue) Start(ctx context.Context) {
	eq.logger.Info("🚀 Starting execution queue processor")

	ticker := time.NewTicker(eq.executionRate)
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			eq.logger.Info("⏹️  Execution queue stopped")
			return
		case <-ticker.C:
			eq.processNext()
		}
	}
}

// processNext processes the next item in the queue
func (eq *ExecutionQueue) processNext() {
	eq.mu.Lock()

	// Check circuit breaker
	if eq.circuitBreaker.IsOpen() {
		eq.mu.Unlock()
		eq.logger.Warn("⚠️  Circuit breaker open, skipping execution")
		return
	}

	if eq.queue.Len() == 0 {
		eq.mu.Unlock()
		return
	}

	item := heap.Pop(eq.queue).(*ExecutionItem)
	eq.mu.Unlock()

	// Execute the opportunity
	success := eq.executeOpportunity(item)

	if success {
		eq.successCount++
		// Convert NetProfit to float64 for tracking
		profitFloat := 0.0
		if item.Opportunity.NetProfit != nil {
			profitEth := new(big.Float).Quo(new(big.Float).SetInt(item.Opportunity.NetProfit), big.NewFloat(1e18))
			var accuracy big.Accuracy
			profitFloat, accuracy = profitEth.Float64()
			// Check if the conversion was exact (accuracy == 0) or if there was a loss of precision
			if accuracy != big.Exact {
				eq.logger.Warn("NetProfit conversion to float64 may have lost precision, accuracy: %v", accuracy)
			}
		}
		eq.totalProfitUSD += profitFloat
		eq.logger.Info(fmt.Sprintf("✅ Execution successful: %.6f ETH profit", profitFloat))
	} else {
		eq.failureCount++
		eq.circuitBreaker.RecordFailure()

		// Retry if not exceeded max retries
		if item.Retries < item.MaxRetries {
			item.Retries++
			item.Priority *= 0.9 // Slightly lower priority for retries

			eq.mu.Lock()
			heap.Push(eq.queue, item)
			eq.mu.Unlock()

			eq.logger.Warn(fmt.Sprintf("🔄 Execution failed, retrying (%d/%d)", item.Retries, item.MaxRetries))
		} else {
			eq.logger.Error("❌ Execution failed after max retries")
		}
	}

	eq.totalExecuted++
}

// executeOpportunity executes a single arbitrage opportunity
func (eq *ExecutionQueue) executeOpportunity(item *ExecutionItem) bool {
	opp := item.Opportunity

	// Convert NetProfit to float64 for logging
	profitFloat := 0.0
	if opp.NetProfit != nil {
		profitEth := new(big.Float).Quo(new(big.Float).SetInt(opp.NetProfit), big.NewFloat(1e18))
		var accuracy big.Accuracy
		profitFloat, accuracy = profitEth.Float64()
		// Check if the conversion was exact (accuracy == 0) or if there was a loss of precision
		if accuracy != big.Exact {
			eq.logger.Warn("NetProfit conversion to float64 may have lost precision, accuracy: %v", accuracy)
		}
	}

	// Get exchange info from path if available
	exchangeInfo := "multi-DEX"
	if len(opp.Path) > 0 {
		exchangeInfo = fmt.Sprintf("%d-hop", len(opp.Path))
	}

	eq.logger.Info(fmt.Sprintf("⚡ Executing arbitrage: %s path, %.6f ETH profit",
		exchangeInfo, profitFloat))

	// TODO: Implement actual execution logic
	// For now, simulate execution with success probability based on confidence
	simulatedSuccess := opp.Confidence > ConfidenceThresholdForSuccess // 70% confidence threshold

	// Simulate execution time
	time.Sleep(SimulatedExecutionTime)

	return simulatedSuccess
}

// IsOpen checks if the circuit breaker is open
func (cb *CircuitBreaker) IsOpen() bool {
	cb.mu.Lock()
	defer cb.mu.Unlock()

	// Clean old failures
	now := time.Now()
	validFailures := make([]time.Time, 0)
	for _, failure := range cb.failures {
		if now.Sub(failure) < cb.timeWindow {
			validFailures = append(validFailures, failure)
		}
	}
	cb.failures = validFailures

	// Check if we should open the circuit breaker
	if len(cb.failures) >= cb.maxFailures {
		cb.isOpen = true
	} else {
		cb.isOpen = false
	}

	return cb.isOpen
}

// RecordFailure records a failed execution
func (cb *CircuitBreaker) RecordFailure() {
	cb.mu.Lock()
	defer cb.mu.Unlock()

	cb.failures = append(cb.failures, time.Now())
}

// GetStats returns execution queue statistics
func (eq *ExecutionQueue) GetStats() map[string]interface{} {
	eq.mu.RLock()
	defer eq.mu.RUnlock()

	successRate := 0.0
	if eq.totalExecuted > 0 {
		successRate = float64(eq.successCount) / float64(eq.totalExecuted) * 100
	}

	return map[string]interface{}{
		"queue_size":           eq.queue.Len(),
		"total_executed":       eq.totalExecuted,
		"success_count":        eq.successCount,
		"failure_count":        eq.failureCount,
		"success_rate":         successRate,
		"total_profit_usd":     eq.totalProfitUSD,
		"circuit_breaker_open": eq.circuitBreaker.IsOpen(),
	}
}