package engine

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"sync"
	"sync/atomic"
	"time"

	"cellbot/internal/protocol"

	"go.uber.org/zap"
)

// Subscription 订阅信息
type Subscription struct {
	ID         string
	Chan       chan protocol.Event
	Filter     func(protocol.Event) bool
	CreatedAt  time.Time
	EventCount int64 // 接收的事件数量
}

// EventBusMetrics 事件总线指标
type EventBusMetrics struct {
	PublishedTotal  int64 // 发布的事件总数
	DispatchedTotal int64 // 分发的事件总数
	DroppedTotal    int64 // 丢弃的事件总数
	SubscriberTotal int64 // 订阅者总数
	LastEventTime   int64 // 最后一次事件时间（Unix时间戳）
}

// EventBus 事件总线
// 基于channel的高性能发布订阅实现
type EventBus struct {
	subscriptions map[string][]*Subscription
	mu            sync.RWMutex
	logger        *zap.Logger
	eventChan     chan protocol.Event
	wg            sync.WaitGroup
	ctx           context.Context
	cancel        context.CancelFunc
	metrics       EventBusMetrics
	bufferSize    int
}

// NewEventBus 创建事件总线
func NewEventBus(logger *zap.Logger, bufferSize int) *EventBus {
	if bufferSize <= 0 {
		bufferSize = 1000
	}
	ctx, cancel := context.WithCancel(context.Background())
	return &EventBus{
		subscriptions: make(map[string][]*Subscription),
		logger:        logger.Named("eventbus"),
		eventChan:     make(chan protocol.Event, bufferSize),
		ctx:           ctx,
		cancel:        cancel,
		bufferSize:    bufferSize,
	}
}

// Start 启动事件总线
func (eb *EventBus) Start() {
	eb.wg.Add(1)
	go eb.dispatch()
	eb.logger.Info("Event bus started")
}

// Stop 停止事件总线
func (eb *EventBus) Stop() {
	eb.cancel()
	eb.wg.Wait()
	close(eb.eventChan)
	eb.logger.Info("Event bus stopped")
}

// Publish 发布事件
func (eb *EventBus) Publish(event protocol.Event) {
	eb.logger.Info("Publishing event to channel",
		zap.String("event_type", string(event.GetType())),
		zap.String("detail_type", event.GetDetailType()),
		zap.Int("channel_len", len(eb.eventChan)),
		zap.Int("channel_cap", cap(eb.eventChan)))

	select {
	case eb.eventChan <- event:
		atomic.AddInt64(&eb.metrics.PublishedTotal, 1)
		atomic.StoreInt64(&eb.metrics.LastEventTime, time.Now().Unix())
		eb.logger.Info("Event successfully queued",
			zap.String("event_type", string(event.GetType())))
	case <-eb.ctx.Done():
		atomic.AddInt64(&eb.metrics.DroppedTotal, 1)
		eb.logger.Warn("Event bus is shutting down, event dropped",
			zap.String("type", string(event.GetType())))
	default:
		// 如果channel满了，也丢弃事件
		atomic.AddInt64(&eb.metrics.DroppedTotal, 1)
		eb.logger.Warn("Event channel full, event dropped",
			zap.String("type", string(event.GetType())),
			zap.Int("buffer_size", eb.bufferSize),
			zap.Int("channel_len", len(eb.eventChan)))
	}
}

// PublishBatch 批量发布事件
func (eb *EventBus) PublishBatch(events []protocol.Event) {
	for _, event := range events {
		eb.Publish(event)
	}
}

// PublishAsync 异步发布事件（不阻塞）
func (eb *EventBus) PublishAsync(event protocol.Event) {
	go eb.Publish(event)
}

// TryPublish 尝试发布事件（非阻塞）
func (eb *EventBus) TryPublish(event protocol.Event) bool {
	select {
	case eb.eventChan <- event:
		atomic.AddInt64(&eb.metrics.PublishedTotal, 1)
		atomic.StoreInt64(&eb.metrics.LastEventTime, time.Now().Unix())
		return true
	case <-eb.ctx.Done():
		atomic.AddInt64(&eb.metrics.DroppedTotal, 1)
		return false
	default:
		atomic.AddInt64(&eb.metrics.DroppedTotal, 1)
		return false
	}
}

// Subscribe 订阅事件
func (eb *EventBus) Subscribe(eventType protocol.EventType, filter func(protocol.Event) bool) chan protocol.Event {
	return eb.SubscribeWithBuffer(eventType, filter, 100)
}

// SubscribeWithBuffer 订阅事件（指定缓冲区大小）
func (eb *EventBus) SubscribeWithBuffer(eventType protocol.EventType, filter func(protocol.Event) bool, bufferSize int) chan protocol.Event {
	eb.mu.Lock()
	defer eb.mu.Unlock()

	if bufferSize <= 0 {
		bufferSize = 100
	}

	sub := &Subscription{
		ID:        generateSubscriptionID(),
		Chan:      make(chan protocol.Event, bufferSize),
		Filter:    filter,
		CreatedAt: time.Now(),
	}

	key := string(eventType)
	eb.subscriptions[key] = append(eb.subscriptions[key], sub)
	atomic.AddInt64(&eb.metrics.SubscriberTotal, 1)

	eb.logger.Debug("New subscription added",
		zap.String("event_type", key),
		zap.String("sub_id", sub.ID),
		zap.Int("buffer_size", bufferSize))

	return sub.Chan
}

// Unsubscribe 取消订阅
func (eb *EventBus) Unsubscribe(eventType protocol.EventType, ch chan protocol.Event) {
	eb.mu.Lock()
	defer eb.mu.Unlock()

	key := string(eventType)
	subs := eb.subscriptions[key]
	for i, sub := range subs {
		if sub.Chan == ch {
			close(sub.Chan)
			eb.subscriptions[key] = append(subs[:i], subs[i+1:]...)
			atomic.AddInt64(&eb.metrics.SubscriberTotal, -1)

			eb.logger.Debug("Subscription removed",
				zap.String("event_type", key),
				zap.String("sub_id", sub.ID),
				zap.Int64("event_count", sub.EventCount),
				zap.Duration("lifetime", time.Since(sub.CreatedAt)))
			return
		}
	}
}

// dispatch 分发事件到订阅者
func (eb *EventBus) dispatch() {
	defer eb.wg.Done()

	eb.logger.Info("Event bus dispatch loop started")

	for {
		select {
		case event, ok := <-eb.eventChan:
			if !ok {
				eb.logger.Info("Event channel closed, stopping dispatch")
				return
			}
			eb.logger.Debug("Received event from channel",
				zap.String("event_type", string(event.GetType())))
			eb.dispatchEvent(event)
		case <-eb.ctx.Done():
			eb.logger.Info("Context cancelled, stopping dispatch")
			return
		}
	}
}

// dispatchEvent 分发单个事件
func (eb *EventBus) dispatchEvent(event protocol.Event) {
	eb.mu.RLock()
	key := string(event.GetType())
	subs := eb.subscriptions[key]
	// 复制订阅者列表避免锁竞争
	subsCopy := make([]*Subscription, len(subs))
	copy(subsCopy, subs)
	eb.mu.RUnlock()

	eb.logger.Info("Dispatching event",
		zap.String("event_type", key),
		zap.String("detail_type", event.GetDetailType()),
		zap.Int("subscriber_count", len(subsCopy)))

	dispatched := 0
	for _, sub := range subsCopy {
		if sub.Filter == nil || sub.Filter(event) {
			select {
			case sub.Chan <- event:
				atomic.AddInt64(&sub.EventCount, 1)
				dispatched++
				eb.logger.Debug("Event dispatched to subscriber",
					zap.String("sub_id", sub.ID))
			default:
				// 订阅者channel已满,丢弃事件
				atomic.AddInt64(&eb.metrics.DroppedTotal, 1)
				eb.logger.Warn("Subscription channel full, event dropped",
					zap.String("sub_id", sub.ID),
					zap.String("event_type", key))
			}
		}
	}

	if dispatched > 0 {
		atomic.AddInt64(&eb.metrics.DispatchedTotal, int64(dispatched))
		eb.logger.Info("Event dispatched successfully",
			zap.String("event_type", key),
			zap.Int("dispatched_count", dispatched))
	} else {
		eb.logger.Warn("No subscribers for event",
			zap.String("event_type", key),
			zap.String("detail_type", event.GetDetailType()))
	}
}

// GetSubscriptionCount 获取订阅者数量
func (eb *EventBus) GetSubscriptionCount(eventType protocol.EventType) int {
	eb.mu.RLock()
	defer eb.mu.RUnlock()
	return len(eb.subscriptions[string(eventType)])
}

// Clear 清空所有订阅
func (eb *EventBus) Clear() {
	eb.mu.Lock()
	defer eb.mu.Unlock()

	for eventType, subs := range eb.subscriptions {
		for _, sub := range subs {
			close(sub.Chan)
		}
		delete(eb.subscriptions, eventType)
	}
	eb.logger.Info("All subscriptions cleared")
}

// GetMetrics 获取事件总线指标
func (eb *EventBus) GetMetrics() EventBusMetrics {
	return EventBusMetrics{
		PublishedTotal:  atomic.LoadInt64(&eb.metrics.PublishedTotal),
		DispatchedTotal: atomic.LoadInt64(&eb.metrics.DispatchedTotal),
		DroppedTotal:    atomic.LoadInt64(&eb.metrics.DroppedTotal),
		SubscriberTotal: atomic.LoadInt64(&eb.metrics.SubscriberTotal),
		LastEventTime:   atomic.LoadInt64(&eb.metrics.LastEventTime),
	}
}

// GetAllSubscriptions 获取所有订阅信息
func (eb *EventBus) GetAllSubscriptions() map[string]int {
	eb.mu.RLock()
	defer eb.mu.RUnlock()

	result := make(map[string]int)
	for eventType, subs := range eb.subscriptions {
		result[eventType] = len(subs)
	}
	return result
}

// GetBufferUsage 获取缓冲区使用情况
func (eb *EventBus) GetBufferUsage() float64 {
	return float64(len(eb.eventChan)) / float64(eb.bufferSize)
}

// IsHealthy 检查事件总线健康状态
func (eb *EventBus) IsHealthy() bool {
	// 检查缓冲区使用率是否过高
	if eb.GetBufferUsage() > 0.9 {
		return false
	}

	// 检查是否有过多的丢弃事件
	metrics := eb.GetMetrics()
	if metrics.PublishedTotal > 0 {
		dropRate := float64(metrics.DroppedTotal) / float64(metrics.PublishedTotal)
		if dropRate > 0.1 { // 丢弃率超过10%
			return false
		}
	}

	return true
}

// LogMetrics 记录指标日志
func (eb *EventBus) LogMetrics() {
	metrics := eb.GetMetrics()
	subs := eb.GetAllSubscriptions()

	eb.logger.Info("EventBus metrics",
		zap.Int64("published_total", metrics.PublishedTotal),
		zap.Int64("dispatched_total", metrics.DispatchedTotal),
		zap.Int64("dropped_total", metrics.DroppedTotal),
		zap.Int64("subscriber_total", metrics.SubscriberTotal),
		zap.Float64("buffer_usage", eb.GetBufferUsage()),
		zap.Any("subscriptions", subs))
}

// generateSubscriptionID 生成订阅ID
func generateSubscriptionID() string {
	return "sub-" + randomString(8)
}

// randomString 生成随机字符串
func randomString(length int) string {
	b := make([]byte, length/2)
	if _, err := rand.Read(b); err != nil {
		// 降级到简单实现
		const charset = "abcdefghijklmnopqrstuvwxyz0123456789"
		result := make([]byte, length)
		for i := range result {
			result[i] = charset[i%len(charset)]
		}
		return string(result)
	}
	return hex.EncodeToString(b)
}