package ws

import (
	"encoding/json"
	"sync"
	"sync/atomic"
	"time"

	"go.uber.org/zap"
)

const (
	defaultUserBufferSize = 128
	maxReplayEvents       = 200
)

// Event 表示一个WebSocket事件
type Event struct {
	ID      uint64      `json:"event_id"`
	Type    string      `json:"type"`
	Event   string      `json:"event"` // 事件名称（兼容多种协议）
	TS      int64       `json:"ts"`
	Payload interface{} `json:"payload"`
}

// Client 表示一个WebSocket客户端连接
type Client struct {
	ID     uint64
	UserID string
	Send   chan []byte
	Quit   chan struct{}
}

// Message 表示WebSocket消息
type Message struct {
	Type    string          `json:"type"`
	Payload json.RawMessage `json:"payload"`
}

// ResponseMessage 表示发送给客户端的消息
type ResponseMessage struct {
	EventID uint64      `json:"event_id"`
	Type    string      `json:"type"`
	TS      int64       `json:"ts"`
	Payload interface{} `json:"payload,omitempty"`
}

// ErrorMessage 表示错误消息
type ErrorMessage struct {
	Type    string `json:"type"`
	Payload struct {
		Code    string `json:"code"`
		Message string `json:"message"`
	} `json:"payload"`
}

// subscriber 表示一个事件订阅者
type subscriber struct {
	id   uint64
	ch   chan Event
	quit chan struct{}
}

// Hub WebSocket连接管理器
type Hub struct {
	seq uint64

	mu          sync.RWMutex
	clients     map[string]map[uint64]*Client // userID -> clientID -> Client
	history     map[string][]Event            // userID -> []Event (用于断线重连历史回放)
	subscribers map[string]map[uint64]*subscriber // userID -> subscriberID -> subscriber
}

// NewHub 创建WebSocket Hub
func NewHub() *Hub {
	return &Hub{
		clients:     make(map[string]map[uint64]*Client),
		history:     make(map[string][]Event),
		subscribers: make(map[string]map[uint64]*subscriber),
	}
}

// NextID 获取下一个事件ID
func (h *Hub) NextID() uint64 {
	return atomic.AddUint64(&h.seq, 1)
}

// Register 注册客户端连接
func (h *Hub) Register(client *Client) []Event {
	h.mu.Lock()
	defer h.mu.Unlock()

	if _, ok := h.clients[client.UserID]; !ok {
		h.clients[client.UserID] = make(map[uint64]*Client)
	}
	h.clients[client.UserID][client.ID] = client

	// 获取历史事件用于回放
	replay := make([]Event, 0)
	for _, e := range h.history[client.UserID] {
		replay = append(replay, e)
	}

	zap.L().Debug("WebSocket client registered",
		zap.String("user_id", client.UserID),
		zap.Uint64("client_id", client.ID),
		zap.Int("total_clients", len(h.clients[client.UserID])),
	)

	return replay
}

// Unregister 注销客户端连接
func (h *Hub) Unregister(client *Client) {
	h.mu.Lock()
	defer h.mu.Unlock()

	if userClients, ok := h.clients[client.UserID]; ok {
		if _, exists := userClients[client.ID]; exists {
			delete(userClients, client.ID)
			close(client.Quit)

			if len(userClients) == 0 {
				delete(h.clients, client.UserID)
			}

			zap.L().Debug("WebSocket client unregistered",
				zap.String("user_id", client.UserID),
				zap.Uint64("client_id", client.ID),
			)
		}
	}
}

// HasClients 检查用户是否有活跃连接
func (h *Hub) HasClients(userID string) bool {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return len(h.clients[userID]) > 0
}

// GetClientCount 获取用户的连接数
func (h *Hub) GetClientCount(userID string) int {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return len(h.clients[userID])
}

// PublishToUser 向指定用户发送事件
func (h *Hub) PublishToUser(userID string, eventType string, payload interface{}) Event {
	ev := Event{
		ID:      h.NextID(),
		Type:    eventType,
		TS:      time.Now().UnixMilli(),
		Payload: payload,
	}
	h.publish(userID, ev)
	return ev
}

// PublishToUsers 向多个用户发送事件
func (h *Hub) PublishToUsers(userIDs []string, eventType string, payload interface{}) {
	for _, uid := range userIDs {
		h.PublishToUser(uid, eventType, payload)
	}
}

// publish 内部发布方法
func (h *Hub) publish(userID string, ev Event) {
	h.mu.Lock()
	// 存储历史事件（最多保留200条）
	history := append(h.history[userID], ev)
	if len(history) > maxReplayEvents {
		history = history[len(history)-maxReplayEvents:]
	}
	h.history[userID] = history

	// 复制客户端列表避免锁竞争
	targets := make([]*Client, 0, len(h.clients[userID]))
	for _, c := range h.clients[userID] {
		targets = append(targets, c)
	}
	h.mu.Unlock()

	// 构建消息
	msg := ResponseMessage{
		EventID: ev.ID,
		Type:    ev.Type,
		TS:      ev.TS,
		Payload: ev.Payload,
	}
	data, err := json.Marshal(msg)
	if err != nil {
		zap.L().Error("Failed to marshal WebSocket message",
			zap.String("user_id", userID),
			zap.String("event_type", ev.Type),
			zap.Error(err),
		)
		return
	}

	// 非阻塞发送，慢消费者丢弃消息
	for _, c := range targets {
		select {
		case <-c.Quit:
			// 客户端已断开
		case c.Send <- data:
			// 消息已发送
		default:
			// 发送缓冲区满，丢弃消息
			zap.L().Warn("WebSocket client buffer full, dropping message",
				zap.String("user_id", userID),
				zap.Uint64("client_id", c.ID),
			)
		}
	}
}

// SendError 向客户端发送错误消息
func (h *Hub) SendError(client *Client, code string, message string) {
	errMsg := ErrorMessage{
		Type: "error",
	}
	errMsg.Payload.Code = code
	errMsg.Payload.Message = message

	data, err := json.Marshal(errMsg)
	if err != nil {
		return
	}

	select {
	case <-client.Quit:
	case client.Send <- data:
	default:
	}
}

// Broadcast 广播消息给所有连接
func (h *Hub) Broadcast(eventType string, payload interface{}) {
	h.mu.RLock()
	userIDs := make([]string, 0, len(h.clients))
	for uid := range h.clients {
		userIDs = append(userIDs, uid)
	}
	h.mu.RUnlock()

	h.PublishToUsers(userIDs, eventType, payload)
}

// GetOnlineUsers 获取在线用户列表
func (h *Hub) GetOnlineUsers() []string {
	h.mu.RLock()
	defer h.mu.RUnlock()

	users := make([]string, 0, len(h.clients))
	for uid := range h.clients {
		users = append(users, uid)
	}
	return users
}

// GetOnlineCount 获取在线用户数
func (h *Hub) GetOnlineCount() int {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return len(h.clients)
}

// Subscribe 订阅事件
func (h *Hub) Subscribe(userID string, afterID uint64) (chan Event, func(), []Event) {
	subID := h.NextID()
	sub := &subscriber{
		id:   subID,
		ch:   make(chan Event, defaultUserBufferSize),
		quit: make(chan struct{}),
	}

	h.mu.Lock()
	if _, ok := h.subscribers[userID]; !ok {
		h.subscribers[userID] = make(map[uint64]*subscriber)
	}
	h.subscribers[userID][subID] = sub

	replay := make([]Event, 0)
	for _, e := range h.history[userID] {
		if e.ID > afterID {
			replay = append(replay, e)
		}
	}
	h.mu.Unlock()

	cancel := func() {
		h.mu.Lock()
		defer h.mu.Unlock()
		if userSubs, ok := h.subscribers[userID]; ok {
			if s, exists := userSubs[subID]; exists {
				close(s.quit)
				delete(userSubs, subID)
				close(s.ch)
			}
			if len(userSubs) == 0 {
				delete(h.subscribers, userID)
			}
		}
	}

	return sub.ch, cancel, replay
}

// EncodeData 编码事件数据
func EncodeData(ev Event) (string, error) {
	body, err := json.Marshal(ev.Payload)
	if err != nil {
		return "", err
	}
	return string(body), nil
}