package instance

import (
	"fmt"
	"os"
	"os/exec"
	"strings"
	"syscall"

	"golang.org/x/sys/windows"
)

func Detach() error {
	if AlreadyRunning() {
		return fmt.Errorf("agent already running")
	}
	exe, err := os.Executable()
	if err != nil {
		return err
	}
	nul, err := os.OpenFile("NUL", os.O_RDWR, 0)
	if err != nil {
		return err
	}
	defer nul.Close()

	cmd := exec.Command(exe, stripBackground(os.Args[1:])...)
	cmd.Stdin = nul
	cmd.Stdout = nul
	cmd.Stderr = nul
	cmd.SysProcAttr = &syscall.SysProcAttr{
		HideWindow:    true,
		CreationFlags: windows.CREATE_NO_WINDOW | windows.CREATE_NEW_PROCESS_GROUP,
	}
	return cmd.Start()
}

func stripBackground(args []string) []string {
	out := make([]string, 0, len(args))
	for _, arg := range args {
		name := strings.TrimLeft(arg, "-/")
		lower := strings.ToLower(name)
		if lower == "background" || strings.HasPrefix(lower, "background=") {
			continue
		}
		out = append(out, arg)
	}
	return out
}