package e2e

// 并发残留压测：多观看端并发穿透后全部离场(混合断开方式), 目标端必须
// 零连接残留, 且隧道立即恢复可用——断开同步的正确性验收。

import (
	"fmt"
	"io"
	"net"
	"sync"
	"sync/atomic"
	"testing"
	"time"
)

// countedEcho 计数回显目标: 跟踪存活连接数与峰值, 连接保持到对端关闭。
type countedEcho struct {
	ln   net.Listener
	live atomic.Int64
	peak atomic.Int64
}

func startCountedEcho(t *testing.T) *countedEcho {
	t.Helper()
	ln, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatal(err)
	}
	t.Cleanup(func() { ln.Close() })
	ce := &countedEcho{ln: ln}
	go func() {
		for {
			c, err := ln.Accept()
			if err != nil {
				return
			}
			go func(c net.Conn) {
				defer c.Close()
				cur := ce.live.Add(1)
				defer ce.live.Add(-1)
				for { // 峰值 CAS 刷高
					p := ce.peak.Load()
					if cur <= p || ce.peak.CompareAndSwap(p, cur) {
						break
					}
				}
				io.Copy(c, c)
			}(c)
		}
	}()
	return ce
}

// TestConcurrentViewersNoTargetLeak 50 观看端并发穿透、三种离场方式
// (干净 FIN / RST 崩溃 / 迟走), 全部离场后目标端零残留, 隧道立即可复用。
func TestConcurrentViewersNoTargetLeak(t *testing.T) {
	n, a := startEnv(t)
	ce := startCountedEcho(t)
	_, port := mustRegister(t, n, a, ce.ln.Addr().String())

	const viewers = 50
	var wg sync.WaitGroup
	var mu sync.Mutex
	var late []net.Conn // 迟走者: 并发段结束后统一关闭

	for i := 0; i < viewers; i++ {
		wg.Add(1)
		go func(i int) {
			defer wg.Done()
			conn, err := net.DialTimeout("tcp", fmt.Sprintf("127.0.0.1:%d", port), 3*time.Second)
			if err != nil {
				t.Errorf("观看端%d 拨号失败: %v", i, err)
				return
			}
			_ = conn.SetDeadline(time.Now().Add(5 * time.Second))
			payload := []byte(fmt.Sprintf("viewer-%02d", i))
			if _, err := conn.Write(payload); err != nil {
				t.Errorf("观看端%d 写失败: %v", i, err)
				conn.Close()
				return
			}
			got := make([]byte, len(payload))
			if _, err := io.ReadFull(conn, got); err != nil {
				t.Errorf("观看端%d 读回失败: %v", i, err)
				conn.Close()
				return
			}
			switch i % 3 {
			case 0: // 干净 FIN(页面正常关闭)
				conn.Close()
			case 1: // RST 硬断(观看端进程崩溃)
				if tc, ok := conn.(*net.TCPConn); ok {
					tc.SetLinger(0)
				}
				conn.Close()
			default: // 迟走: 压测段结束后统一关
				mu.Lock()
				late = append(late, conn)
				mu.Unlock()
			}
		}(i)
	}
	wg.Wait()
	t.Logf("并发 %d 观看端完成往返: 目标端存活=%d 峰值=%d", viewers, ce.live.Load(), ce.peak.Load())

	for _, c := range late {
		c.Close()
	}

	deadline := time.Now().Add(10 * time.Second)
	for time.Now().Before(deadline) {
		if ce.live.Load() == 0 {
			break
		}
		time.Sleep(100 * time.Millisecond)
	}
	if left := ce.live.Load(); left != 0 {
		t.Fatalf("全部观看端离场后目标端残留 %d 条连接(应为 0)", left)
	}

	// 隧道压测后立即可复用: 新观看端一轮完整往返
	if got := roundTrip(t, port, []byte("after-storm")); string(got) != "after-storm" {
		t.Fatalf("压测后隧道不可用, 回读=%q", got)
	}
}