package bus

import (
	"github.com/yourname/cyrene-ai/pkg/logger"
	"sync"
	"time"
)

// Bus 总线接口（方便测试和替换）
type Bus interface {
	Publish(event BusEvent)
	Subscribe(eventType EventType, handler EventHandler) *Subscription
}

// ConversationBus 对话事件总线
// Step 1: 仅 side-channel 发布，无消费端
type ConversationBus struct {
	mu          sync.RWMutex
	subscribers map[EventType][]*Subscription
	eventCh     chan BusEvent
	done        chan struct{}
}

// NewConversationBus 创建总线
func NewConversationBus() *ConversationBus {
	b := &ConversationBus{
		subscribers: make(map[EventType][]*Subscription),
		eventCh:     make(chan BusEvent, 64),
		done:        make(chan struct{}),
	}
	go b.dispatchLoop()
	return b
}

// Publish 发布事件到总线（非阻塞）
func (b *ConversationBus) Publish(event BusEvent) {
	if event.Timestamp.IsZero() {
		event.Timestamp = time.Now()
	}
	select {
	case b.eventCh <- event:
	default:
		logger.Printf("[bus] 事件通道已满，丢弃事件: type=%s session=%s", event.Type, event.SessionID)
	}
}

// Subscribe 订阅事件类型
func (b *ConversationBus) Subscribe(eventType EventType, handler EventHandler) *Subscription {
	b.mu.Lock()
	defer b.mu.Unlock()
	sub := &Subscription{bus: b, eventType: eventType, handler: handler}
	b.subscribers[eventType] = append(b.subscribers[eventType], sub)
	return sub
}

// unsubscribe 内部取消订阅
func (b *ConversationBus) unsubscribe(sub *Subscription) {
	b.mu.Lock()
	defer b.mu.Unlock()
	subs := b.subscribers[sub.eventType]
	for i, s := range subs {
		if s == sub {
			b.subscribers[sub.eventType] = append(subs[:i], subs[i+1:]...)
			break
		}
	}
}

// Stop 停止总线
func (b *ConversationBus) Stop() {
	close(b.done)
}

// dispatchLoop 后台分发循环
func (b *ConversationBus) dispatchLoop() {
	for {
		select {
		case event := <-b.eventCh:
			b.mu.RLock()
			subs := b.subscribers[event.Type]
			// 拷贝一份避免持锁回调
			handlers := make([]EventHandler, len(subs))
			for i, s := range subs {
				handlers[i] = s.handler
			}
			b.mu.RUnlock()
			for _, h := range handlers {
				func() {
					defer func() {
						if r := recover(); r != nil {
							logger.Printf("[bus] handler panic: %v", r)
						}
					}()
					h(event)
				}()
			}
		case <-b.done:
			return
		}
	}
}