package chat

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

	"github.com/gorilla/websocket"
)

const (
	writeWait           = 10 * time.Second
	pongWait            = 60 * time.Second
	pingPeriod          = (pongWait * 9) / 10
	maxMessageSize      = 512
	roomQueueBufferSize = 2048
	historyLimit        = 100
)

type Message struct {
	Type      string `json:"type"` // "chat", "system", "danmaku"
	Username  string `json:"username"`
	Content   string `json:"content"`
	RoomID    string `json:"room_id"`
	IsHistory bool   `json:"is_history"`
}

type Client struct {
	Hub      *Hub
	Conn     *websocket.Conn
	Send     chan []byte
	RoomID   string
	Username string
}

type Hub struct {
	mutex sync.RWMutex
	rooms map[string]*roomHub
}

type roomHub struct {
	roomID       string
	manager      *Hub
	register     chan *Client
	unregister   chan *Client
	broadcast    chan Message
	clearHistory chan struct{}
	stop         chan struct{}
	stopOnce     sync.Once

	mutex   sync.RWMutex
	clients map[*Client]struct{}
	history []Message
}

type StatsSnapshot struct {
	RoomCount            int            `json:"room_count"`
	TotalConnectedClient int            `json:"total_connected_client"`
	RoomClients          map[string]int `json:"room_clients"`
}

func NewHub() *Hub {
	return &Hub{
		rooms: make(map[string]*roomHub),
	}
}

func (h *Hub) getRoom(roomID string) *roomHub {
	h.mutex.RLock()
	room := h.rooms[roomID]
	h.mutex.RUnlock()
	return room
}

func (h *Hub) getOrCreateRoom(roomID string) *roomHub {
	if room := h.getRoom(roomID); room != nil {
		return room
	}

	h.mutex.Lock()
	defer h.mutex.Unlock()

	if room := h.rooms[roomID]; room != nil {
		return room
	}

	room := &roomHub{
		roomID:       roomID,
		manager:      h,
		register:     make(chan *Client, roomQueueBufferSize),
		unregister:   make(chan *Client, roomQueueBufferSize),
		broadcast:    make(chan Message, roomQueueBufferSize),
		clearHistory: make(chan struct{}, 1),
		stop:         make(chan struct{}),
		clients:      make(map[*Client]struct{}),
	}
	h.rooms[roomID] = room
	go room.run()
	return room
}

func (h *Hub) deleteRoomIfIdle(room *roomHub) {
	room.mutex.RLock()
	idle := len(room.clients) == 0 && len(room.history) == 0
	room.mutex.RUnlock()
	if !idle {
		return
	}

	h.mutex.Lock()
	if current := h.rooms[room.roomID]; current == room {
		delete(h.rooms, room.roomID)
		room.stopOnce.Do(func() {
			close(room.stop)
		})
	}
	h.mutex.Unlock()
}

func (r *roomHub) run() {
	for {
		select {
		case client := <-r.register:
			r.handleRegister(client)
		case client := <-r.unregister:
			r.handleUnregister(client)
		case message := <-r.broadcast:
			r.handleBroadcast(message)
		case <-r.clearHistory:
			r.handleClearHistory()
		case <-r.stop:
			return
		}
	}
}

func (r *roomHub) handleRegister(client *Client) {
	r.mutex.RLock()
	historyCopy := make([]Message, len(r.history))
	copy(historyCopy, r.history)
	r.mutex.RUnlock()

	for _, msg := range historyCopy {
		msg.IsHistory = true
		msgBytes, err := json.Marshal(msg)
		if err != nil {
			continue
		}
		select {
		case client.Send <- msgBytes:
		default:
		}
	}

	r.mutex.Lock()
	r.clients[client] = struct{}{}
	r.mutex.Unlock()
}

func (r *roomHub) handleUnregister(client *Client) {
	r.mutex.Lock()
	if _, ok := r.clients[client]; ok {
		delete(r.clients, client)
		close(client.Send)
	}
	r.mutex.Unlock()

	r.manager.deleteRoomIfIdle(r)
}

func (r *roomHub) handleBroadcast(message Message) {
	msgBytes, err := json.Marshal(message)
	if err != nil {
		return
	}

	r.mutex.Lock()
	if message.Type == "chat" || message.Type == "danmaku" {
		r.history = append(r.history, message)
		if len(r.history) > historyLimit {
			r.history = r.history[1:]
		}
	}

	for client := range r.clients {
		select {
		case client.Send <- msgBytes:
		default:
			close(client.Send)
			delete(r.clients, client)
		}
	}
	r.mutex.Unlock()
}

func (r *roomHub) handleClearHistory() {
	r.mutex.Lock()
	r.history = nil
	r.mutex.Unlock()
	r.manager.deleteRoomIfIdle(r)
}

func (h *Hub) ClearRoomHistory(roomID string) {
	if room := h.getRoom(roomID); room != nil {
		select {
		case room.clearHistory <- struct{}{}:
		default:
		}
	}
}

func (h *Hub) RegisterClient(c *Client) {
	h.getOrCreateRoom(c.RoomID).register <- c
}

func (h *Hub) UnregisterClient(c *Client) {
	if room := h.getRoom(c.RoomID); room != nil {
		room.unregister <- c
	}
}

func (h *Hub) BroadcastToRoom(msg Message) {
	h.getOrCreateRoom(msg.RoomID).broadcast <- msg
}

func (c *Client) ReadPump() {
	defer func() {
		c.Hub.UnregisterClient(c)
		c.Conn.Close()
	}()
	c.Conn.SetReadLimit(maxMessageSize)
	c.Conn.SetReadDeadline(time.Now().Add(pongWait))
	c.Conn.SetPongHandler(func(string) error {
		c.Conn.SetReadDeadline(time.Now().Add(pongWait))
		return nil
	})
	for {
		_, message, err := c.Conn.ReadMessage()
		if err != nil {
			break
		}
		var msg Message
		if err := json.Unmarshal(message, &msg); err == nil {
			msg.RoomID = c.RoomID
			msg.Username = c.Username
			c.Hub.BroadcastToRoom(msg)
		}
	}
}

func (c *Client) WritePump() {
	ticker := time.NewTicker(pingPeriod)
	defer func() {
		ticker.Stop()
		c.Conn.Close()
	}()
	for {
		select {
		case message, ok := <-c.Send:
			c.Conn.SetWriteDeadline(time.Now().Add(writeWait))
			if !ok {
				c.Conn.WriteMessage(websocket.CloseMessage, []byte{})
				return
			}
			w, err := c.Conn.NextWriter(websocket.TextMessage)
			if err != nil {
				return
			}
			if _, err := w.Write(message); err != nil {
				_ = w.Close()
				return
			}
			if err := w.Close(); err != nil {
				return
			}
		case <-ticker.C:
			c.Conn.SetWriteDeadline(time.Now().Add(writeWait))
			if err := c.Conn.WriteMessage(websocket.PingMessage, nil); err != nil {
				return
			}
		}
	}
}

var MainHub *Hub

func InitChat() {
	MainHub = NewHub()
}

func (h *Hub) GetStatsSnapshot() StatsSnapshot {
	h.mutex.RLock()
	rooms := make([]*roomHub, 0, len(h.rooms))
	roomClients := make(map[string]int, len(h.rooms))
	for roomID, room := range h.rooms {
		rooms = append(rooms, room)
		roomClients[roomID] = 0
	}
	h.mutex.RUnlock()

	totalClients := 0
	for _, room := range rooms {
		room.mutex.RLock()
		count := len(room.clients)
		room.mutex.RUnlock()
		roomClients[room.roomID] = count
		totalClients += count
	}

	return StatsSnapshot{
		RoomCount:            len(rooms),
		TotalConnectedClient: totalClients,
		RoomClients:          roomClients,
	}
}