package transport

import (
	"fmt"
	"math/rand"
	"sort"
	"sync"
	"time"
)

// MessageRouter handles intelligent message routing and transport selection
type MessageRouter struct {
	rules        []RoutingRule
	fallback     TransportType
	loadBalancer LoadBalancer
	mu           sync.RWMutex
}

// RoutingRule defines message routing logic
type RoutingRule struct {
	ID         string
	Name       string
	Condition  MessageFilter
	Transport  TransportType
	Priority   int
	Enabled    bool
	Created    time.Time
	LastUsed   time.Time
	UsageCount int64
}

// RouteMessage selects the appropriate transport for a message
func (mr *MessageRouter) RouteMessage(msg *Message, transports map[TransportType]Transport) (Transport, error) {
	mr.mu.RLock()
	defer mr.mu.RUnlock()

	// Find matching rules (sorted by priority)
	matchingRules := mr.findMatchingRules(msg)

	// Try each matching rule in priority order
	for _, rule := range matchingRules {
		if transport, exists := transports[rule.Transport]; exists {
			// Check transport health
			if health := transport.Health(); health.Status == "healthy" {
				mr.updateRuleUsage(rule.ID)
				return transport, nil
			}
		}
	}

	// Use load balancer for available transports
	if mr.loadBalancer != nil {
		availableTransports := mr.getHealthyTransports(transports)
		if len(availableTransports) > 0 {
			selectedType := mr.loadBalancer.SelectTransport(availableTransports, msg)
			if transport, exists := transports[selectedType]; exists {
				return transport, nil
			}
		}
	}

	// Fall back to default transport
	if fallbackTransport, exists := transports[mr.fallback]; exists {
		if health := fallbackTransport.Health(); health.Status != "unhealthy" {
			return fallbackTransport, nil
		}
	}

	return nil, fmt.Errorf("no available transport for message")
}

// AddRule adds a new routing rule
func (mr *MessageRouter) AddRule(rule RoutingRule) {
	mr.mu.Lock()
	defer mr.mu.Unlock()

	if rule.ID == "" {
		rule.ID = fmt.Sprintf("rule_%d", time.Now().UnixNano())
	}
	rule.Created = time.Now()
	rule.Enabled = true

	mr.rules = append(mr.rules, rule)
	mr.sortRulesByPriority()
}

// RemoveRule removes a routing rule by ID
func (mr *MessageRouter) RemoveRule(ruleID string) bool {
	mr.mu.Lock()
	defer mr.mu.Unlock()

	for i, rule := range mr.rules {
		if rule.ID == ruleID {
			mr.rules = append(mr.rules[:i], mr.rules[i+1:]...)
			return true
		}
	}
	return false
}

// UpdateRule updates an existing routing rule
func (mr *MessageRouter) UpdateRule(ruleID string, updates func(*RoutingRule)) bool {
	mr.mu.Lock()
	defer mr.mu.Unlock()

	for i := range mr.rules {
		if mr.rules[i].ID == ruleID {
			updates(&mr.rules[i])
			mr.sortRulesByPriority()
			return true
		}
	}
	return false
}

// GetRules returns all routing rules
func (mr *MessageRouter) GetRules() []RoutingRule {
	mr.mu.RLock()
	defer mr.mu.RUnlock()

	rules := make([]RoutingRule, len(mr.rules))
	copy(rules, mr.rules)
	return rules
}

// EnableRule enables a routing rule
func (mr *MessageRouter) EnableRule(ruleID string) bool {
	return mr.UpdateRule(ruleID, func(rule *RoutingRule) {
		rule.Enabled = true
	})
}

// DisableRule disables a routing rule
func (mr *MessageRouter) DisableRule(ruleID string) bool {
	return mr.UpdateRule(ruleID, func(rule *RoutingRule) {
		rule.Enabled = false
	})
}

// SetFallbackTransport sets the fallback transport type
func (mr *MessageRouter) SetFallbackTransport(transportType TransportType) {
	mr.mu.Lock()
	defer mr.mu.Unlock()
	mr.fallback = transportType
}

// SetLoadBalancer sets the load balancer
func (mr *MessageRouter) SetLoadBalancer(lb LoadBalancer) {
	mr.mu.Lock()
	defer mr.mu.Unlock()
	mr.loadBalancer = lb
}

// Private helper methods

func (mr *MessageRouter) findMatchingRules(msg *Message) []RoutingRule {
	var matching []RoutingRule

	for _, rule := range mr.rules {
		if rule.Enabled && (rule.Condition == nil || rule.Condition(msg)) {
			matching = append(matching, rule)
		}
	}

	return matching
}

func (mr *MessageRouter) sortRulesByPriority() {
	sort.Slice(mr.rules, func(i, j int) bool {
		return mr.rules[i].Priority > mr.rules[j].Priority
	})
}

func (mr *MessageRouter) updateRuleUsage(ruleID string) {
	for i := range mr.rules {
		if mr.rules[i].ID == ruleID {
			mr.rules[i].LastUsed = time.Now()
			mr.rules[i].UsageCount++
			break
		}
	}
}

func (mr *MessageRouter) getHealthyTransports(transports map[TransportType]Transport) []TransportType {
	var healthy []TransportType

	for transportType, transport := range transports {
		if health := transport.Health(); health.Status == "healthy" {
			healthy = append(healthy, transportType)
		}
	}

	return healthy
}

// LoadBalancer implementations

// RoundRobinLoadBalancer implements round-robin load balancing
type RoundRobinLoadBalancer struct {
	counter int64
	mu      sync.Mutex
}

func NewRoundRobinLoadBalancer() *RoundRobinLoadBalancer {
	return &RoundRobinLoadBalancer{}
}

func (lb *RoundRobinLoadBalancer) SelectTransport(transports []TransportType, msg *Message) TransportType {
	if len(transports) == 0 {
		return ""
	}

	lb.mu.Lock()
	defer lb.mu.Unlock()

	selected := transports[lb.counter%int64(len(transports))]
	lb.counter++
	return selected
}

func (lb *RoundRobinLoadBalancer) UpdateStats(transport TransportType, latency time.Duration, success bool) {
	// Round-robin doesn't use stats
}

// WeightedLoadBalancer implements weighted load balancing based on performance
type WeightedLoadBalancer struct {
	stats map[TransportType]*TransportStats
	mu    sync.RWMutex
}

type TransportStats struct {
	TotalRequests   int64
	SuccessRequests int64
	TotalLatency    time.Duration
	LastUpdate      time.Time
	Weight          float64
}

func NewWeightedLoadBalancer() *WeightedLoadBalancer {
	return &WeightedLoadBalancer{
		stats: make(map[TransportType]*TransportStats),
	}
}

func (lb *WeightedLoadBalancer) SelectTransport(transports []TransportType, msg *Message) TransportType {
	if len(transports) == 0 {
		return ""
	}

	lb.mu.RLock()
	defer lb.mu.RUnlock()

	// Calculate weights and select based on weighted random selection
	totalWeight := 0.0
	weights := make(map[TransportType]float64)

	for _, transport := range transports {
		weight := lb.calculateWeight(transport)
		weights[transport] = weight
		totalWeight += weight
	}

	if totalWeight == 0 {
		// Fall back to random selection
		return transports[rand.Intn(len(transports))]
	}

	// Weighted random selection
	target := rand.Float64() * totalWeight
	current := 0.0

	for _, transport := range transports {
		current += weights[transport]
		if current >= target {
			return transport
		}
	}

	// Fallback (shouldn't happen)
	return transports[0]
}

func (lb *WeightedLoadBalancer) UpdateStats(transport TransportType, latency time.Duration, success bool) {
	lb.mu.Lock()
	defer lb.mu.Unlock()

	stats, exists := lb.stats[transport]
	if !exists {
		stats = &TransportStats{
			Weight: 1.0, // Default weight
		}
		lb.stats[transport] = stats
	}

	stats.TotalRequests++
	stats.TotalLatency += latency
	stats.LastUpdate = time.Now()

	if success {
		stats.SuccessRequests++
	}

	// Recalculate weight based on performance
	stats.Weight = lb.calculateWeight(transport)
}

func (lb *WeightedLoadBalancer) calculateWeight(transport TransportType) float64 {
	stats, exists := lb.stats[transport]
	if !exists {
		return 1.0 // Default weight for unknown transports
	}

	if stats.TotalRequests == 0 {
		return 1.0
	}

	// Calculate success rate
	successRate := float64(stats.SuccessRequests) / float64(stats.TotalRequests)

	// Calculate average latency
	avgLatency := stats.TotalLatency / time.Duration(stats.TotalRequests)

	// Weight formula: success rate / (latency factor)
	// Lower latency and higher success rate = higher weight
	latencyFactor := float64(avgLatency) / float64(time.Millisecond)
	if latencyFactor < 1 {
		latencyFactor = 1
	}

	weight := successRate / latencyFactor

	// Ensure minimum weight
	if weight < 0.1 {
		weight = 0.1
	}

	return weight
}

// LeastLatencyLoadBalancer selects the transport with the lowest latency
type LeastLatencyLoadBalancer struct {
	stats map[TransportType]*LatencyStats
	mu    sync.RWMutex
}

type LatencyStats struct {
	RecentLatencies []time.Duration
	MaxSamples      int
	LastUpdate      time.Time
}

func NewLeastLatencyLoadBalancer() *LeastLatencyLoadBalancer {
	return &LeastLatencyLoadBalancer{
		stats: make(map[TransportType]*LatencyStats),
	}
}

func (lb *LeastLatencyLoadBalancer) SelectTransport(transports []TransportType, msg *Message) TransportType {
	if len(transports) == 0 {
		return ""
	}

	lb.mu.RLock()
	defer lb.mu.RUnlock()

	bestTransport := transports[0]
	bestLatency := time.Hour // Large initial value

	for _, transport := range transports {
		avgLatency := lb.getAverageLatency(transport)
		if avgLatency < bestLatency {
			bestLatency = avgLatency
			bestTransport = transport
		}
	}

	return bestTransport
}

func (lb *LeastLatencyLoadBalancer) UpdateStats(transport TransportType, latency time.Duration, success bool) {
	if !success {
		return // Only track successful requests
	}

	lb.mu.Lock()
	defer lb.mu.Unlock()

	stats, exists := lb.stats[transport]
	if !exists {
		stats = &LatencyStats{
			RecentLatencies: make([]time.Duration, 0),
			MaxSamples:      10, // Keep last 10 samples
		}
		lb.stats[transport] = stats
	}

	// Add new latency sample
	stats.RecentLatencies = append(stats.RecentLatencies, latency)

	// Keep only recent samples
	if len(stats.RecentLatencies) > stats.MaxSamples {
		stats.RecentLatencies = stats.RecentLatencies[1:]
	}

	stats.LastUpdate = time.Now()
}

func (lb *LeastLatencyLoadBalancer) getAverageLatency(transport TransportType) time.Duration {
	stats, exists := lb.stats[transport]
	if !exists || len(stats.RecentLatencies) == 0 {
		return time.Millisecond * 100 // Default estimate
	}

	total := time.Duration(0)
	for _, latency := range stats.RecentLatencies {
		total += latency
	}

	return total / time.Duration(len(stats.RecentLatencies))
}

// Common routing rule factory functions

// CreateTopicRule creates a rule based on message topic
func CreateTopicRule(name string, topic string, transport TransportType, priority int) RoutingRule {
	return RoutingRule{
		Name:      name,
		Condition: func(msg *Message) bool { return msg.Topic == topic },
		Transport: transport,
		Priority:  priority,
	}
}

// CreateTopicPatternRule creates a rule based on topic pattern matching
func CreateTopicPatternRule(name string, pattern string, transport TransportType, priority int) RoutingRule {
	return RoutingRule{
		Name: name,
		Condition: func(msg *Message) bool {
			// Simple pattern matching (can be enhanced with regex)
			return msg.Topic == pattern ||
				(len(pattern) > 0 && pattern[len(pattern)-1] == '*' &&
					len(msg.Topic) >= len(pattern)-1 &&
					msg.Topic[:len(pattern)-1] == pattern[:len(pattern)-1])
		},
		Transport: transport,
		Priority:  priority,
	}
}

// CreatePriorityRule creates a rule based on message priority
func CreatePriorityRule(name string, msgPriority MessagePriority, transport TransportType, priority int) RoutingRule {
	return RoutingRule{
		Name:      name,
		Condition: func(msg *Message) bool { return msg.Priority == msgPriority },
		Transport: transport,
		Priority:  priority,
	}
}

// CreateTypeRule creates a rule based on message type
func CreateTypeRule(name string, msgType MessageType, transport TransportType, priority int) RoutingRule {
	return RoutingRule{
		Name:      name,
		Condition: func(msg *Message) bool { return msg.Type == msgType },
		Transport: transport,
		Priority:  priority,
	}
}

// CreateSourceRule creates a rule based on message source
func CreateSourceRule(name string, source string, transport TransportType, priority int) RoutingRule {
	return RoutingRule{
		Name:      name,
		Condition: func(msg *Message) bool { return msg.Source == source },
		Transport: transport,
		Priority:  priority,
	}
}