package engine

import (
	"context"
	"sync"

	"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
}

// 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
}

// NewEventBus 创建事件总线
func NewEventBus(logger *zap.Logger, bufferSize int) *EventBus {
	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,
	}
}

// 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) {
	select {
	case eb.eventChan <- event:
	case <-eb.ctx.Done():
		eb.logger.Warn("Event bus is shutting down, event dropped",
			zap.String("type", string(event.GetType())))
	}
}

// Subscribe 订阅事件
func (eb *EventBus) Subscribe(eventType protocol.EventType, filter func(protocol.Event) bool) chan protocol.Event {
	eb.mu.Lock()
	defer eb.mu.Unlock()

	sub := &Subscription{
		ID:     generateSubscriptionID(),
		Chan:   make(chan protocol.Event, 100),
		Filter: filter,
	}

	key := string(eventType)
	eb.subscriptions[key] = append(eb.subscriptions[key], sub)

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

	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:]...)
			eb.logger.Debug("Subscription removed",
				zap.String("event_type", key),
				zap.String("sub_id", sub.ID))
			return
		}
	}
}

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

	for {
		select {
		case event, ok := <-eb.eventChan:
			if !ok {
				return
			}
			eb.dispatchEvent(event)
		case <-eb.ctx.Done():
			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()

	for _, sub := range subsCopy {
		if sub.Filter == nil || sub.Filter(event) {
			select {
			case sub.Chan <- event:
			default:
				// 订阅者channel已满,丢弃事件
				eb.logger.Warn("Subscription channel full, event dropped",
					zap.String("sub_id", sub.ID),
					zap.String("event_type", key))
			}
		}
	}
}

// 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")
}

// 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 {
	const charset = "abcdefghijklmnopqrstuvwxyz0123456789"
	b := make([]byte, length)
	for i := range b {
		b[i] = charset[i%len(charset)]
	}
	return string(b)
}