// Package server 实现 WebSocket 服务器，管理硬件设备连接的生命周期。
package server

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"log"
	"net"
	"net/http"
	"sync"

	"github.com/gorilla/websocket"
	"github.com/qy/hw-ws-service/internal/connection"
	"github.com/qy/hw-ws-service/internal/handler"
	"github.com/qy/hw-ws-service/internal/rtcclient"
)

const (
	// maxConnections 最大并发连接数，防止资源耗尽。
	maxConnections = 500
	// maxMessageBytes WebSocket 单条消息上限（4KB），防止内存耗尽攻击。
	maxMessageBytes = 4 * 1024
)

var upgrader = websocket.Upgrader{
	ReadBufferSize:  1024,
	WriteBufferSize: 1024,
	// IoT 设备无浏览器 Origin，允许所有来源
	CheckOrigin: func(r *http.Request) bool { return true },
}

// Server 管理所有活跃的设备连接。
type Server struct {
	client     *rtcclient.Client
	httpServer *http.Server

	mu    sync.Mutex
	conns map[string]*connection.Connection // key: DeviceID
	wg    sync.WaitGroup                   // 跟踪所有连接 goroutine
}

// New 创建 Server，addr 形如 "0.0.0.0:8888"。
func New(addr string, client *rtcclient.Client) *Server {
	s := &Server{
		client: client,
		conns:  make(map[string]*connection.Connection),
	}

	mux := http.NewServeMux()
	mux.HandleFunc("/xiaozhi/v1/healthz", s.handleStatus)
	mux.HandleFunc("/xiaozhi/v1/", s.handleConn)
	mux.HandleFunc("/healthz", func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(http.StatusOK)
	})

	s.httpServer = &http.Server{
		Addr:    addr,
		Handler: mux,
	}
	return s
}

// ListenAndServe 启动服务器，阻塞直到服务器关闭。
func (s *Server) ListenAndServe() error {
	log.Printf("server: listening on %s", s.httpServer.Addr)
	err := s.httpServer.ListenAndServe()
	if errors.Is(err, http.ErrServerClosed) {
		return nil
	}
	return err
}

// Shutdown 优雅关闭：先停止接受新连接，再等待所有连接 goroutine 退出。
func (s *Server) Shutdown(ctx context.Context) {
	log.Println("server: shutting down...")
	s.httpServer.Shutdown(ctx) //nolint:errcheck

	// 等待所有连接 goroutine 退出（由 ctx 超时兜底）
	done := make(chan struct{})
	go func() {
		s.wg.Wait()
		close(done)
	}()

	select {
	case <-done:
		log.Println("server: all connections closed gracefully")
	case <-ctx.Done():
		log.Println("server: shutdown timeout, forcing close")
	}
}

// handleConn 处理单个 WebSocket 连接的完整生命周期。
// URL 格式：/xiaozhi/v1/?device-id=<MAC>&client-id=<UUID>
func (s *Server) handleConn(w http.ResponseWriter, r *http.Request) {
	deviceID := r.URL.Query().Get("device-id")
	clientID := r.URL.Query().Get("client-id")

	if deviceID == "" {
		http.Error(w, "missing device-id", http.StatusBadRequest)
		return
	}

	ws, err := upgrader.Upgrade(w, r, nil)
	if err != nil {
		log.Printf("server: upgrade failed for %s: %v", deviceID, err)
		return
	}

	// 设置单条消息大小上限
	ws.SetReadLimit(maxMessageBytes)

	conn := connection.New(ws, deviceID, clientID)

	if err := s.register(conn); err != nil {
		log.Printf("server: register %s failed: %v", deviceID, err)
		ws.Close()
		return
	}

	s.wg.Add(1)
	defer func() {
		conn.StopPlayback()
		s.unregister(deviceID)
		ws.Close()
		s.wg.Done()
		log.Printf("server: device %s disconnected, active=%d", deviceID, s.activeCount())
	}()

	log.Printf("server: device %s connected, active=%d", deviceID, s.activeCount())

	// 消息读取循环
	for {
		msgType, raw, err := ws.ReadMessage()
		if err != nil {
			if !websocket.IsCloseError(err, websocket.CloseNormalClosure, websocket.CloseGoingAway) {
				if !isNetworkClose(err) {
					log.Printf("server: read error for %s: %v", deviceID, err)
				}
			}
			return
		}

		// 只处理文本消息（二进制为上行音频，本服务暂不处理）
		if msgType != websocket.TextMessage {
			continue
		}

		var envelope struct {
			Type string `json:"type"`
		}
		if err := json.Unmarshal(raw, &envelope); err != nil {
			log.Printf("server: invalid json from %s: %v", deviceID, err)
			continue
		}

		switch envelope.Type {
		case "story":
			go handler.HandleStory(conn, s.client)
		default:
			log.Printf("server: unhandled message type %q from %s", envelope.Type, deviceID)
		}
	}
}

// register 注册连接，若同一设备已有连接则踢掉旧连接。
func (s *Server) register(conn *connection.Connection) error {
	s.mu.Lock()
	defer s.mu.Unlock()

	if len(s.conns) >= maxConnections {
		return errors.New("server: max connections reached")
	}

	// 同一设备同时只允许一个连接
	if old, exists := s.conns[conn.DeviceID]; exists {
		log.Printf("server: kicking old connection for %s", conn.DeviceID)
		old.Close()
	}

	s.conns[conn.DeviceID] = conn
	return nil
}

func (s *Server) unregister(deviceID string) {
	s.mu.Lock()
	defer s.mu.Unlock()
	delete(s.conns, deviceID)
}

func (s *Server) activeCount() int {
	s.mu.Lock()
	defer s.mu.Unlock()
	return len(s.conns)
}

// handleStatus 返回服务状态和当前活跃连接数，用于部署后验证。
// GET /xiaozhi/v1/healthz → {"status":"ok","active_connections":N}
func (s *Server) handleStatus(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(http.StatusOK)
	active := s.activeCount()
	fmt.Fprintf(w, `{"status":"ok","active_connections":%d}`, active)
}

// isNetworkClose 判断是否为普通的网络关闭错误（不需要打印日志）。
func isNetworkClose(err error) bool {
	var netErr *net.OpError
	return errors.As(err, &netErr)
}