// 扫描状态 WebSocket 实时推送端点。
package api

import (
	"encoding/json"
	"net/http"
	"time"

	"github.com/gin-gonic/gin"
	"github.com/gorilla/websocket"
)

// wsUpgrader WebSocket 升级器
var wsUpgrader = websocket.Upgrader{
	ReadBufferSize:  1024,
	WriteBufferSize: 4096,
	// 同源管理页，允许任意来源，便于局域网访问
	CheckOrigin: func(r *http.Request) bool { return true },
}

const (
	wsWriteWait  = 10 * time.Second
	wsPongWait   = 60 * time.Second
	wsPingPeriod = (wsPongWait * 9) / 10
)

// Ws GET /api/scan/ws 建立 WebSocket 连接，持续推送扫描状态。
// 连接建立后立即推送当前状态快照；断开后前端可自动重连（服务端不做重连保证）。
func (c *ScanController) Ws(ctx *gin.Context) {
	conn, err := wsUpgrader.Upgrade(ctx.Writer, ctx.Request, nil)
	if err != nil {
		return
	}
	ch, cancel := c.service.Subscribe()
	defer func() {
		cancel()
		conn.Close()
	}()

	// 读协程：仅用于感知客户端断开/失活（配合 pong 心跳），不处理业务消息
	conn.SetReadLimit(1024)
	_ = conn.SetReadDeadline(time.Now().Add(wsPongWait))
	conn.SetPongHandler(func(string) error {
		return conn.SetReadDeadline(time.Now().Add(wsPongWait))
	})

	// 写协程：先推送快照，再转发订阅更新，并周期性 ping 保活
	writeDone := make(chan struct{})
	go func() {
		defer close(writeDone)
		write := func(msgType int, data []byte) bool {
			if err := conn.WriteMessage(msgType, data); err != nil {
				conn.Close() // 写失败即断开，让读协程退出
				return false
			}
			return true
		}
		if b, err := json.Marshal(c.service.Status()); err == nil {
			if !write(websocket.TextMessage, b) {
				return
			}
		}
		ticker := time.NewTicker(wsPingPeriod)
		defer ticker.Stop()
		for {
			select {
			case st, ok := <-ch:
				if !ok {
					return
				}
				b, err := json.Marshal(st)
				if err != nil {
					continue
				}
				if !write(websocket.TextMessage, b) {
					return
				}
			case <-ticker.C:
				if !write(websocket.PingMessage, nil) {
					return
				}
			}
		}
	}()

	for {
		if _, _, err := conn.ReadMessage(); err != nil {
			break
		}
	}
	cancel() // 先关闭订阅频道，让写协程退出，避免 <-writeDone 永久阻塞
	<-writeDone
}