//go:build windows

// Package prereboot ensures the reboot-resume infrastructure is in place
// before xetup triggers a system restart mid-deployment.
package prereboot

import (
	"fmt"
	"io"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"syscall"

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

// StablePath is where xetup.exe is copied so it survives across reboots.
const StablePath = `C:\Windows\Setup\Scripts\xetup.exe`

// TaskName is the scheduled task that re-launches xetup after each reboot.
const TaskName = "X9-Resume"

const adminUser = "adminx9"
const winlogonKey = `SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon`

// IsAdminx9 reports whether the current process runs as the adminx9 account.
func IsAdminx9() bool {
	return strings.EqualFold(os.Getenv("USERNAME"), adminUser)
}

// Prepare ensures the reboot-resume infrastructure is in place.
// When not running as adminx9 (first reboot trigger):
//   - creates the adminx9 local account if it does not exist
//   - copies the running binary to StablePath
//   - enables autologon for adminx9 (AutoLogonCount=20 safety cap)
//   - registers the X9-Resume scheduled task (AtLogOn adminx9, RunLevel Highest)
//
// When already running as adminx9 (subsequent rounds) all of the above is
// already in place; the function returns immediately without changes.
// Safe to call repeatedly (idempotent).
func Prepare() error {
	if IsAdminx9() {
		return nil
	}
	if err := ensureAdminx9User(); err != nil {
		return fmt.Errorf("adminx9 account: %w", err)
	}
	if err := copySelfTo(StablePath); err != nil {
		return fmt.Errorf("copy binary: %w", err)
	}
	if err := setAutologon(); err != nil {
		return fmt.Errorf("autologon: %w", err)
	}
	if err := registerResumeTask(); err != nil {
		return fmt.Errorf("resume task: %w", err)
	}
	return nil
}

// Cleanup disables autologon and removes the X9-Resume scheduled task.
// Called when all deployment steps have completed successfully.
func Cleanup() {
	_ = disableAutologon()
	_ = unregisterResumeTask()
}

// ensureAdminx9User creates the adminx9 local account if absent.
func ensureAdminx9User() error {
	// "net user adminx9" exits 0 when user exists
	if err := newHiddenCmd("net", "user", adminUser).Run(); err == nil {
		return nil // already exists
	}
	// Create with empty password
	if b, err := newHiddenCmd("net", "user", adminUser, "", "/add").CombinedOutput(); err != nil {
		return fmt.Errorf("net user /add: %s: %w", strings.TrimSpace(string(b)), err)
	}
	// Add to local Administrators group
	if b, err := newHiddenCmd("net", "localgroup", "Administrators", adminUser, "/add").CombinedOutput(); err != nil {
		return fmt.Errorf("net localgroup: %s: %w", strings.TrimSpace(string(b)), err)
	}
	// Hide from the Windows login screen
	k, _, err := registry.CreateKey(registry.LOCAL_MACHINE,
		`SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\UserList`,
		registry.SET_VALUE)
	if err != nil {
		return fmt.Errorf("registry hide: %w", err)
	}
	defer k.Close()
	return k.SetDWordValue(adminUser, 0)
}

// copySelfTo copies the running executable to dst.
// Skips the copy when src and dst resolve to the same path.
func copySelfTo(dst string) error {
	src, err := os.Executable()
	if err != nil {
		return err
	}
	if resolved, err := filepath.EvalSymlinks(src); err == nil {
		src = resolved
	}
	if strings.EqualFold(src, dst) {
		return nil
	}
	if err := os.MkdirAll(filepath.Dir(dst), 0755); err != nil {
		return err
	}
	return copyFile(src, dst)
}

func copyFile(src, dst string) error {
	r, err := os.Open(src)
	if err != nil {
		return err
	}
	defer r.Close()
	w, err := os.Create(dst)
	if err != nil {
		return err
	}
	defer w.Close()
	_, err = io.Copy(w, r)
	return err
}

func setAutologon() error {
	k, err := registry.OpenKey(registry.LOCAL_MACHINE, winlogonKey, registry.SET_VALUE)
	if err != nil {
		return err
	}
	defer k.Close()
	for _, kv := range []struct{ name, val string }{
		{"AutoAdminLogon", "1"},
		{"DefaultUserName", adminUser},
		{"DefaultPassword", ""},
		{"DefaultDomainName", "."},
	} {
		if err := k.SetStringValue(kv.name, kv.val); err != nil {
			return fmt.Errorf("set %s: %w", kv.name, err)
		}
	}
	// Safety cap: self-limits even if cleanup task fails to run
	return k.SetDWordValue("AutoLogonCount", 20)
}

func disableAutologon() error {
	k, err := registry.OpenKey(registry.LOCAL_MACHINE, winlogonKey, registry.SET_VALUE)
	if err != nil {
		return err
	}
	defer k.Close()
	_ = k.SetStringValue("AutoAdminLogon", "0")
	_ = k.DeleteValue("DefaultPassword")
	_ = k.DeleteValue("AutoLogonCount")
	return nil
}

func registerResumeTask() error {
	ps := fmt.Sprintf(`
$action    = New-ScheduledTaskAction -Execute '%s' -Argument '--resume'
$trigger   = New-ScheduledTaskTrigger -AtLogOn -User '%s'
$settings  = New-ScheduledTaskSettingsSet -ExecutionTimeLimit (New-TimeSpan -Hours 4) -MultipleInstances IgnoreNew
$principal = New-ScheduledTaskPrincipal -UserId '%s' -LogonType Interactive -RunLevel Highest
Unregister-ScheduledTask -TaskName 'X9-Resume' -Confirm:$false -ErrorAction SilentlyContinue
Register-ScheduledTask -TaskName 'X9-Resume' -Action $action -Trigger $trigger -Settings $settings -Principal $principal -Force | Out-Null
`, StablePath, adminUser, adminUser)
	return runPS(ps)
}

func unregisterResumeTask() error {
	return runPS(`Unregister-ScheduledTask -TaskName 'X9-Resume' -Confirm:$false -ErrorAction SilentlyContinue`)
}

func runPS(script string) error {
	cmd := newHiddenCmd("powershell.exe",
		"-NonInteractive", "-ExecutionPolicy", "Bypass", "-Command", script)
	b, err := cmd.CombinedOutput()
	if err != nil {
		return fmt.Errorf("%s: %w", strings.TrimSpace(string(b)), err)
	}
	return nil
}

func newHiddenCmd(name string, args ...string) *exec.Cmd {
	cmd := exec.Command(name, args...)
	cmd.SysProcAttr = &syscall.SysProcAttr{HideWindow: true}
	return cmd
}