package chat

import (
	"context"
	"sync"

	"github.com/google/uuid"
	"go.uber.org/zap"
)

type Hub struct {
	clients         map[*Client]bool
	rooms           map[uuid.UUID]map[*Client]bool
	userIndex       map[uuid.UUID][]*Client
	register        chan *Client
	unregister      chan *Client
	broadcast       chan *RoomBroadcast
	done            chan struct{} // TASK-DEBT-008: lifecycle - close to stop Run()
	mu              sync.RWMutex
	logger          *zap.Logger
	presenceService *ChatPresenceService
}

type RoomBroadcast struct {
	RoomID  uuid.UUID
	Data    []byte
	Exclude *Client
}

func NewHub(logger *zap.Logger, presenceService *ChatPresenceService) *Hub {
	if logger == nil {
		logger = zap.NewNop()
	}
	return &Hub{
		clients:         make(map[*Client]bool),
		rooms:           make(map[uuid.UUID]map[*Client]bool),
		userIndex:       make(map[uuid.UUID][]*Client),
		register:        make(chan *Client),
		unregister:      make(chan *Client),
		broadcast:       make(chan *RoomBroadcast, 256),
		done:            make(chan struct{}),
		logger:          logger,
		presenceService: presenceService,
	}
}

func (h *Hub) Run() {
	for {
		select {
		case <-h.done:
			return
		case client := <-h.register:
			h.mu.Lock()
			h.clients[client] = true
			h.userIndex[client.UserID] = append(h.userIndex[client.UserID], client)
			h.mu.Unlock()

			if h.presenceService != nil {
				_ = h.presenceService.SetOnline(context.Background(), client.UserID)
			}

			h.logger.Info("Client registered",
				zap.String("user_id", client.UserID.String()))

		case client := <-h.unregister:
			h.mu.Lock()
			userOffline := false
			if _, ok := h.clients[client]; ok {
				delete(h.clients, client)
				close(client.send)

				for roomID, members := range h.rooms {
					delete(members, client)
					if len(members) == 0 {
						delete(h.rooms, roomID)
					}
				}

				clients := h.userIndex[client.UserID]
				for i, c := range clients {
					if c == client {
						h.userIndex[client.UserID] = append(clients[:i], clients[i+1:]...)
						break
					}
				}
				if len(h.userIndex[client.UserID]) == 0 {
					delete(h.userIndex, client.UserID)
					userOffline = true
				}
			}
			h.mu.Unlock()

			if h.presenceService != nil && userOffline {
				_ = h.presenceService.SetOffline(context.Background(), client.UserID)
			}

			h.logger.Info("Client unregistered",
				zap.String("user_id", client.UserID.String()))

		case msg := <-h.broadcast:
			h.mu.RLock()
			members, ok := h.rooms[msg.RoomID]
			if ok {
				for client := range members {
					if msg.Exclude != nil && client == msg.Exclude {
						continue
					}
					select {
					case client.send <- msg.Data:
					default:
						go func(c *Client) {
							h.unregister <- c
						}(client)
					}
				}
			}
			h.mu.RUnlock()
		}
	}
}

func (h *Hub) JoinRoom(client *Client, roomID uuid.UUID) {
	h.mu.Lock()
	defer h.mu.Unlock()

	if h.rooms[roomID] == nil {
		h.rooms[roomID] = make(map[*Client]bool)
	}
	h.rooms[roomID][client] = true
}

func (h *Hub) LeaveRoom(client *Client, roomID uuid.UUID) {
	h.mu.Lock()
	defer h.mu.Unlock()

	if members, ok := h.rooms[roomID]; ok {
		delete(members, client)
		if len(members) == 0 {
			delete(h.rooms, roomID)
		}
	}
}

func (h *Hub) BroadcastToRoom(roomID uuid.UUID, data []byte, exclude *Client) {
	h.broadcast <- &RoomBroadcast{
		RoomID:  roomID,
		Data:    data,
		Exclude: exclude,
	}
}

func (h *Hub) SendToUser(userID uuid.UUID, data []byte) {
	h.mu.RLock()
	defer h.mu.RUnlock()

	clients, ok := h.userIndex[userID]
	if !ok {
		return
	}

	for _, client := range clients {
		select {
		case client.send <- data:
		default:
		}
	}
}

func (h *Hub) SendToClient(client *Client, data []byte) {
	select {
	case client.send <- data:
	default:
	}
}

func (h *Hub) Register(client *Client) {
	h.register <- client
}

func (h *Hub) Unregister(client *Client) {
	h.unregister <- client
}

func (h *Hub) IsUserOnline(userID uuid.UUID) bool {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return len(h.userIndex[userID]) > 0
}

func (h *Hub) GetRoomMembers(roomID uuid.UUID) []*Client {
	h.mu.RLock()
	defer h.mu.RUnlock()

	members, ok := h.rooms[roomID]
	if !ok {
		return nil
	}

	result := make([]*Client, 0, len(members))
	for client := range members {
		result = append(result, client)
	}
	return result
}

func (h *Hub) GetConnectedUsersCount() int {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return len(h.userIndex)
}

// Shutdown stops the Hub's Run loop (TASK-DEBT-008: goroutine lifecycle)
func (h *Hub) Shutdown() {
	close(h.done)
}