//go:build linux

package version

import (
	"bufio"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"strconv"
	"strings"
	"syscall"
	"testing"
	"time"

	"github.com/stretchr/testify/require"
	"golang.org/x/sys/unix"
)

const updaterPTYRoleEnv = "MPV_MANAGER_TEST_UPDATER_PTY_ROLE"

func environmentWithUpdaterPTYRole(role string) []string {
	environment := make([]string, 0, len(os.Environ())+1)
	for _, entry := range os.Environ() {
		name, _, _ := strings.Cut(entry, "=")
		if name != updaterPTYRoleEnv {
			environment = append(environment, entry)
		}
	}
	return append(environment, updaterPTYRoleEnv+"="+role)
}

func TestUpdaterTerminalDescriptorsSurviveHelperRelaunch(t *testing.T) {
	switch os.Getenv(updaterPTYRoleEnv) {
	case "helper":
		child := attachUpdateTerminal(exec.Command(os.Args[0], "-test.run=^TestUpdaterTerminalDescriptorsSurviveHelperRelaunch$"))
		child.Env = environmentWithUpdaterPTYRole("child")
		if err := child.Run(); err != nil {
			t.Fatalf("PTY child failed: %v", err)
		}
		return
	case "child":
		if _, err := unix.IoctlGetTermios(int(os.Stdout.Fd()), unix.TCGETS); err != nil {
			t.Fatalf("relaunch output is not a terminal: %v", err)
		}
		fmt.Fprintln(os.Stdout, "FIRST-FRAME")
		line, err := bufio.NewReader(os.Stdin).ReadString('\n')
		if err != nil {
			t.Fatalf("read terminal input: %v", err)
		}
		fmt.Fprintln(os.Stdout, "INPUT:"+strings.TrimSpace(line))
		return
	}

	masterFD, err := unix.Open("/dev/ptmx", unix.O_RDWR|unix.O_CLOEXEC, 0)
	if err != nil {
		t.Skipf("open native PTY: %v", err)
	}
	master := os.NewFile(uintptr(masterFD), "ptmx")
	require.NotNil(t, master)
	defer master.Close()
	require.NoError(t, unix.IoctlSetPointerInt(masterFD, unix.TIOCSPTLCK, 0))
	ptyNumber, err := unix.IoctlGetInt(masterFD, unix.TIOCGPTN)
	require.NoError(t, err)
	slave, err := os.OpenFile(filepath.Join("/dev/pts", strconv.Itoa(ptyNumber)), os.O_RDWR, 0)
	require.NoError(t, err)

	helper := exec.Command(os.Args[0], "-test.run=^TestUpdaterTerminalDescriptorsSurviveHelperRelaunch$")
	helper.Env = environmentWithUpdaterPTYRole("helper")
	func() {
		oldStdin, oldStdout, oldStderr := os.Stdin, os.Stdout, os.Stderr
		defer func() { os.Stdin, os.Stdout, os.Stderr = oldStdin, oldStdout, oldStderr }()
		os.Stdin, os.Stdout, os.Stderr = slave, slave, slave
		attachUpdateTerminal(helper)
	}()
	helper.SysProcAttr = &syscall.SysProcAttr{Setsid: true, Setctty: true, Ctty: 0}
	require.NoError(t, helper.Start())
	require.NoError(t, slave.Close())

	lines := make(chan string, 16)
	go func() {
		scanner := bufio.NewScanner(master)
		for scanner.Scan() {
			lines <- scanner.Text()
		}
		close(lines)
	}()
	waitForLine := func(fragment string) {
		t.Helper()
		deadline := time.After(8 * time.Second)
		for {
			select {
			case line, ok := <-lines:
				if !ok {
					t.Fatalf("PTY closed before %q", fragment)
				}
				if strings.Contains(line, fragment) {
					return
				}
			case <-deadline:
				_ = helper.Process.Kill()
				t.Fatalf("timed out waiting for PTY output %q", fragment)
			}
		}
	}

	waitForLine("FIRST-FRAME")
	_, err = master.Write([]byte("probe-input\n"))
	require.NoError(t, err)
	waitForLine("INPUT:probe-input")
	require.NoError(t, helper.Wait())
}