//go:build windows

// Package service integrates gpu-turnstile with the Windows Service
// Control Manager: running as a service with graceful stop, plus
// install/remove helpers.
package service

import (
	"context"
	"fmt"
	"os"
	"time"

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

// Name is the Windows service name.
const Name = "gpu-turnstile"

// IsService reports whether the process is running as a Windows service.
func IsService() bool {
	isSvc, err := svc.IsWindowsService()
	return err == nil && isSvc
}

// Run executes run as a Windows service. SCM Stop and Shutdown cancel the
// context passed to run, triggering the same graceful shutdown as SIGTERM
// in interactive mode.
func Run(run func(ctx context.Context) error) error {
	return svc.Run(Name, &handler{run: run})
}

type handler struct {
	run func(ctx context.Context) error
}

func (h *handler) Execute(_ []string, requests <-chan svc.ChangeRequest, status chan<- svc.Status) (bool, uint32) {
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()

	status <- svc.Status{State: svc.StartPending}
	errCh := make(chan error, 1)
	go func() { errCh <- h.run(ctx) }()
	status <- svc.Status{State: svc.Running, Accepts: svc.AcceptStop | svc.AcceptShutdown}

	for {
		select {
		case err := <-errCh:
			status <- svc.Status{State: svc.Stopped}
			if err != nil {
				return true, 1
			}
			return false, 0
		case c := <-requests:
			switch c.Cmd {
			case svc.Interrogate:
				status <- c.CurrentStatus
			case svc.Stop, svc.Shutdown:
				status <- svc.Status{State: svc.StopPending}
				cancel()
			}
		}
	}
}

// Install registers gpu-turnstile as an auto-start Windows service whose
// binPath loads the given config file. Recovery actions restart the
// service after 5s on failure — this is also what brings up a staged
// update after the updater exits with a non-zero code.
func Install(configPath string) error {
	exe, err := os.Executable()
	if err != nil {
		return err
	}
	m, err := mgr.Connect()
	if err != nil {
		return fmt.Errorf("connect to service manager (run as administrator): %w", err)
	}
	defer m.Disconnect()

	binPath := fmt.Sprintf(`"%s" -config "%s"`, exe, configPath)
	s, err := m.CreateService(Name, binPath, mgr.Config{
		StartType:   mgr.StartAutomatic,
		DisplayName: "gpu-turnstile",
		Description: "GPU arbitration proxy for Ollama and ComfyUI",
	})
	if err != nil {
		return fmt.Errorf("create service: %w", err)
	}
	defer s.Close()

	restart := mgr.RecoveryAction{Type: mgr.ServiceRestart, Delay: 5 * time.Second}
	if err := s.SetRecoveryActions([]mgr.RecoveryAction{restart, restart, restart}, 24*60*60); err != nil {
		return fmt.Errorf("set recovery actions: %w", err)
	}
	if err := s.SetRecoveryActionsOnNonCrashFailures(true); err != nil {
		return fmt.Errorf("set failure actions flag: %w", err)
	}
	return nil
}

// Remove stops (if running) and unregisters the service.
func Remove() error {
	m, err := mgr.Connect()
	if err != nil {
		return fmt.Errorf("connect to service manager (run as administrator): %w", err)
	}
	defer m.Disconnect()
	s, err := m.OpenService(Name)
	if err != nil {
		return fmt.Errorf("open service: %w", err)
	}
	defer s.Close()
	s.Control(svc.Stop) // ignore error: may already be stopped
	if err := s.Delete(); err != nil {
		return fmt.Errorf("delete service: %w", err)
	}
	return nil
}