package load

import (
	"bytes"
	"io"
	"net"
	"testing"
	"time"
)

// 极简 MQTT broker：读 CONNECT，回 CONNACK accepted，保持连接。
func startFakeMQTTBroker(t *testing.T) (addr string, closeFn func()) {
	t.Helper()
	ln, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		t.Fatalf("listen: %v", err)
	}
	done := make(chan struct{})
	go func() {
		for {
			conn, err := ln.Accept()
			if err != nil {
				select {
				case <-done:
					return
				default:
					return
				}
			}
			go func(c net.Conn) {
				defer func() { _ = c.Close() }()
				_ = c.SetDeadline(time.Now().Add(5 * time.Second))
				buf := make([]byte, 256)
				n, err := c.Read(buf)
				if err != nil || n < 2 || buf[0] != 0x10 {
					return
				}
				// CONNACK: type 0x20, remaining 2, flags 0, rc 0
				_, _ = c.Write([]byte{0x20, 0x02, 0x00, 0x00})
				_ = c.SetDeadline(time.Time{})
				_, _ = io.Copy(io.Discard, c)
			}(conn)
		}
	}()
	return ln.Addr().String(), func() {
		close(done)
		_ = ln.Close()
	}
}

func TestMQTTBenchConnectN(t *testing.T) {
	addr, stop := startFakeMQTTBroker(t)
	defer stop()

	var out bytes.Buffer
	b := &MQTTBench{Addr: addr, ClientIDPrefix: "q-t-", Timeout: 2 * time.Second}
	defer b.Close()
	if err := b.ConnectN(3, &out); err != nil {
		t.Fatalf("ConnectN: %v", err)
	}
	if b.Alive() != 3 {
		t.Fatalf("alive=%d", b.Alive())
	}
	got := out.String()
	if !bytes.Contains(out.Bytes(), []byte("mqtt connections: 3")) {
		t.Fatalf("output missing count: %q", got)
	}
}

func TestMQTTBenchRequiresAddr(t *testing.T) {
	b := &MQTTBench{}
	if err := b.ConnectN(1, nil); err == nil {
		t.Fatal("expected error")
	}
}