//go:build windows

package windows

import (
	"context"
	cryptorand "crypto/rand"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"strings"
	"sync"
	"syscall"
	"time"
	"unsafe"

	"github.com/rvbox/rvbox/internal/client/supervisor"
	winapi "golang.org/x/sys/windows"
)

const (
	launcherHandshakeTimeout = 30 * time.Second
	launcherPipeBuffer       = 64 << 10
	launcherPipePrefix       = `\\.\pipe\rvbox-launch-`
)

var (
	procGetNamedPipeClientProcessID = winapi.NewLazySystemDLL("kernel32.dll").NewProc("GetNamedPipeClientProcessId")
	procGetNamedPipeClientSessionID = winapi.NewLazySystemDLL("kernel32.dll").NewProc("GetNamedPipeClientSessionId")
	procIsProcessInJob              = winapi.NewLazySystemDLL("kernel32.dll").NewProc("IsProcessInJob")
)

type launcherPipe struct {
	name string
	file *os.File
}

type launcherPipeSet struct {
	channel    string
	generation [16]byte
	control    launcherPipe
	stdin      launcherPipe
	stdout     launcherPipe
	stderr     launcherPipe
}

func (pipes *launcherPipeSet) closeAll() {
	for _, pipe := range []*launcherPipe{&pipes.control, &pipes.stdin, &pipes.stdout, &pipes.stderr} {
		if pipe.file != nil {
			_ = pipe.file.Close()
			pipe.file = nil
		}
	}
}

func newLauncherPipes(effectiveSID string) (*launcherPipeSet, error) {
	if effectiveSID == "" {
		return nil, errors.New("launcher pipe ACL requires an effective SID")
	}
	if _, err := winapi.StringToSid(effectiveSID); err != nil {
		return nil, fmt.Errorf("invalid effective SID for launcher pipe ACL: %w", err)
	}
	var generation [16]byte
	if _, err := io.ReadFull(cryptorand.Reader, generation[:]); err != nil {
		return nil, fmt.Errorf("generate launcher channel: %w", err)
	}
	channel := hex.EncodeToString(generation[:])
	securityDescriptor, err := winapi.SecurityDescriptorFromString(fmt.Sprintf("O:SYD:(A;;GA;;;SY)(A;;GA;;;%s)", effectiveSID))
	if err != nil {
		return nil, fmt.Errorf("build launcher pipe ACL: %w", err)
	}
	security := &winapi.SecurityAttributes{Length: uint32(unsafe.Sizeof(winapi.SecurityAttributes{})), SecurityDescriptor: securityDescriptor}
	newPipe := func(suffix string, access uint32) (launcherPipe, error) {
		name := launcherPipePrefix + channel + "-" + suffix
		namePtr, err := winapi.UTF16PtrFromString(name)
		if err != nil {
			return launcherPipe{}, err
		}
		mode := uint32(winapi.PIPE_TYPE_BYTE | winapi.PIPE_READMODE_BYTE | winapi.PIPE_WAIT | winapi.PIPE_REJECT_REMOTE_CLIENTS)
		handle, err := winapi.CreateNamedPipe(namePtr, access, mode, 1, launcherPipeBuffer, launcherPipeBuffer, 0, security)
		if err != nil {
			return launcherPipe{}, fmt.Errorf("create launcher pipe %s: %w", suffix, err)
		}
		return launcherPipe{name: name, file: os.NewFile(uintptr(handle), "rvbox-launch-"+suffix)}, nil
	}
	pipes := &launcherPipeSet{channel: channel, generation: generation}
	if pipes.control, err = newPipe("control", winapi.PIPE_ACCESS_DUPLEX); err != nil {
		return nil, err
	}
	if pipes.stdin, err = newPipe("stdin", winapi.PIPE_ACCESS_OUTBOUND); err != nil {
		pipes.closeAll()
		return nil, err
	}
	if pipes.stdout, err = newPipe("stdout", winapi.PIPE_ACCESS_INBOUND); err != nil {
		pipes.closeAll()
		return nil, err
	}
	if pipes.stderr, err = newPipe("stderr", winapi.PIPE_ACCESS_INBOUND); err != nil {
		pipes.closeAll()
		return nil, err
	}
	return pipes, nil
}

type launcherPeer struct {
	PID       uint32
	Creation  uint64
	SessionID uint32
	UserSID   string
}

func processCreation(handle winapi.Handle) (uint64, error) {
	var creation, exit, kernel, user winapi.Filetime
	if err := winapi.GetProcessTimes(handle, &creation, &exit, &kernel, &user); err != nil {
		return 0, err
	}
	return uint64(creation.HighDateTime)<<32 | uint64(creation.LowDateTime), nil
}

func verifyLauncherPipePeer(handle winapi.Handle, expected launcherPeer) error {
	var pid uint32
	if result, _, callErr := procGetNamedPipeClientProcessID.Call(uintptr(handle), uintptr(unsafe.Pointer(&pid))); result == 0 {
		if callErr == syscall.Errno(0) {
			callErr = syscall.GetLastError()
		}
		return fmt.Errorf("query launcher pipe client PID: %w", callErr)
	}
	if pid != expected.PID {
		return fmt.Errorf("launcher pipe client PID %d does not match %d", pid, expected.PID)
	}
	var sessionID uint32
	if result, _, callErr := procGetNamedPipeClientSessionID.Call(uintptr(handle), uintptr(unsafe.Pointer(&sessionID))); result == 0 {
		if callErr == syscall.Errno(0) {
			callErr = syscall.GetLastError()
		}
		return fmt.Errorf("query launcher pipe client session: %w", callErr)
	}
	if sessionID != expected.SessionID {
		return fmt.Errorf("launcher pipe client session %d does not match %d", sessionID, expected.SessionID)
	}
	process, err := winapi.OpenProcess(winapi.PROCESS_QUERY_LIMITED_INFORMATION, false, pid)
	if err != nil {
		return fmt.Errorf("open launcher pipe client process: %w", err)
	}
	defer winapi.CloseHandle(process)
	creation, err := processCreation(process)
	if err != nil {
		return fmt.Errorf("query launcher process creation time: %w", err)
	}
	if creation != expected.Creation {
		return errors.New("launcher pipe client creation time does not match")
	}
	var token winapi.Token
	if err := winapi.OpenProcessToken(process, winapi.TOKEN_QUERY, &token); err != nil {
		return fmt.Errorf("open launcher client token: %w", err)
	}
	defer token.Close()
	user, err := token.GetTokenUser()
	if err != nil || user.User.Sid == nil {
		if err != nil {
			return fmt.Errorf("query launcher client SID: %w", err)
		}
		return errors.New("launcher client token has no SID")
	}
	if user.User.Sid.String() != expected.UserSID {
		return fmt.Errorf("launcher client SID %q does not match %q", user.User.Sid.String(), expected.UserSID)
	}
	return nil
}

func connectLauncherPipe(ctx context.Context, pipe launcherPipe, expected launcherPeer) error {
	handle := winapi.Handle(pipe.file.Fd())
	connected := make(chan error, 1)
	go func() {
		err := winapi.ConnectNamedPipe(handle, nil)
		if err != nil && !errors.Is(err, winapi.ERROR_PIPE_CONNECTED) {
			connected <- err
			return
		}
		connected <- verifyLauncherPipePeer(handle, expected)
	}()
	select {
	case <-ctx.Done():
		return ctx.Err()
	case err := <-connected:
		if err != nil {
			return fmt.Errorf("connect launcher pipe %s: %w", pipe.name, err)
		}
		return nil
	}
}

func acceptLauncherPipes(ctx context.Context, pipes *launcherPipeSet, expected launcherPeer) error {
	results := make(chan error, 4)
	for _, pipe := range []launcherPipe{pipes.control, pipes.stdin, pipes.stdout, pipes.stderr} {
		go func(pipe launcherPipe) { results <- connectLauncherPipe(ctx, pipe, expected) }(pipe)
	}
	for range 4 {
		if err := <-results; err != nil {
			pipes.closeAll()
			return err
		}
	}
	return nil
}

func launcherGeneration(channel string) ([16]byte, error) {
	var generation [16]byte
	if len(channel) != hex.EncodedLen(len(generation)) {
		return generation, errors.New("invalid launcher channel length")
	}
	if _, err := hex.Decode(generation[:], []byte(channel)); err != nil {
		return generation, errors.New("invalid launcher channel encoding")
	}
	return generation, nil
}

func openLauncherPipe(channel, suffix string, access uint32) (*os.File, error) {
	generation, err := launcherGeneration(channel)
	if err != nil {
		return nil, err
	}
	_ = generation
	name, err := winapi.UTF16PtrFromString(launcherPipePrefix + strings.ToLower(channel) + "-" + suffix)
	if err != nil {
		return nil, err
	}
	deadline := time.Now().Add(launcherHandshakeTimeout)
	for {
		handle, openErr := winapi.CreateFile(name, access, 0, nil, winapi.OPEN_EXISTING, 0, 0)
		if openErr == nil {
			return os.NewFile(uintptr(handle), "rvbox-launch-"+suffix), nil
		}
		if time.Now().After(deadline) {
			return nil, fmt.Errorf("open launcher pipe %s: %w", suffix, openErr)
		}
		time.Sleep(10 * time.Millisecond)
	}
}

func (manager *execSupervisor) startViaLauncher(ctx context.Context, spec supervisor.StartSpec, token winapi.Token, identity supervisor.EffectiveIdentity, launch LaunchPlan, cleanup func()) (supervisor.Process, error) {
	pipes, err := newLauncherPipes(identity.UserSID)
	if err != nil {
		if cleanup != nil {
			cleanup()
		}
		return nil, err
	}
	job, err := createKillOnCloseJob()
	if err != nil {
		pipes.closeAll()
		if cleanup != nil {
			cleanup()
		}
		return nil, fmt.Errorf("create command Job: %w", err)
	}
	if err := applyJobProfiles(job, manager.options.JobProfiles, spec.ExecutionProfiles); err != nil {
		_ = winapi.CloseHandle(job)
		pipes.closeAll()
		if cleanup != nil {
			cleanup()
		}
		return nil, err
	}
	closeOnFailure := true
	defer func() {
		if closeOnFailure {
			_ = winapi.TerminateJobObject(job, 1)
			_ = winapi.CloseHandle(job)
			pipes.closeAll()
			if cleanup != nil {
				cleanup()
			}
		}
	}()
	executable := manager.options.ExecutablePath
	if executable == "" {
		executable, err = os.Executable()
		if err != nil {
			return nil, fmt.Errorf("resolve launcher executable: %w", err)
		}
	}
	if err := verifyExecutable(executable); err != nil {
		return nil, fmt.Errorf("verify launcher executable: %w", err)
	}
	launcherApplication, err := winapi.UTF16PtrFromString(executable)
	if err != nil {
		return nil, err
	}
	launcherCommand, err := BuildCommandLine([]string{executable, "--launcher", "--channel", pipes.channel})
	if err != nil {
		return nil, err
	}
	launcherCommandUTF16, err := winapi.UTF16FromString(launcherCommand)
	if err != nil {
		return nil, err
	}
	startup := winapi.StartupInfoEx{StartupInfo: winapi.StartupInfo{Cb: uint32(unsafe.Sizeof(winapi.StartupInfoEx{}))}}
	var launcherInfo winapi.ProcessInformation
	flags := uint32(winapi.CREATE_SUSPENDED | winapi.CREATE_UNICODE_ENVIRONMENT | winapi.EXTENDED_STARTUPINFO_PRESENT | winapi.CREATE_NO_WINDOW)
	if err := winapi.CreateProcessAsUser(token, launcherApplication, &launcherCommandUTF16[0], nil, nil, false, flags, nil, nil, &startup.StartupInfo, &launcherInfo); err != nil {
		return nil, fmt.Errorf("create suspended launcher: %w", err)
	}
	launcherCreated := true
	defer func() {
		if launcherCreated {
			_ = winapi.TerminateProcess(launcherInfo.Process, 1)
			_ = winapi.CloseHandle(launcherInfo.Process)
			_ = winapi.CloseHandle(launcherInfo.Thread)
		}
	}()
	if err := winapi.AssignProcessToJobObject(job, launcherInfo.Process); err != nil {
		return nil, fmt.Errorf("assign launcher to Job: %w", err)
	}
	launcherBirth, err := processCreation(launcherInfo.Process)
	if err != nil {
		return nil, fmt.Errorf("query launcher creation time: %w", err)
	}
	if _, err := winapi.ResumeThread(launcherInfo.Thread); err != nil {
		return nil, fmt.Errorf("resume launcher: %w", err)
	}
	_ = winapi.CloseHandle(launcherInfo.Thread)
	expected := launcherPeer{PID: launcherInfo.ProcessId, Creation: launcherBirth, SessionID: identity.SessionID, UserSID: identity.UserSID}
	handshakeCtx, cancel := context.WithTimeout(ctx, launcherHandshakeTimeout)
	defer cancel()
	if err := acceptLauncherPipes(handshakeCtx, pipes, expected); err != nil {
		return nil, err
	}
	frame, err := readLauncherFrameContext(handshakeCtx, pipes.control.file, pipes.generation)
	if err != nil {
		return nil, fmt.Errorf("read launcher hello: %w", err)
	}
	if frame.Kind != launcherFrameHello {
		return nil, errors.New("launcher did not send hello first")
	}
	var hello launcherHello
	if err := unmarshalLauncherPayload(frame.Payload, &hello); err != nil {
		return nil, fmt.Errorf("decode launcher hello: %w", err)
	}
	if hello.PID != expected.PID || hello.Creation != expected.Creation || hello.SessionID != expected.SessionID || hello.Effective != expected.UserSID {
		return nil, errors.New("launcher hello identity mismatch")
	}
	requestPayload, err := marshalLauncherPayload(launcherRequest{ApplicationName: launch.ApplicationName, CommandLine: launch.CommandLine, WorkingDirectory: launch.WorkingDirectory, Environment: launch.Environment})
	if err != nil {
		return nil, err
	}
	if err := writeLauncherFrame(pipes.control.file, launcherFrame{Kind: launcherFrameLaunch, Generation: pipes.generation, Payload: requestPayload}); err != nil {
		return nil, fmt.Errorf("send launcher request: %w", err)
	}
	frame, err = readLauncherFrameContext(handshakeCtx, pipes.control.file, pipes.generation)
	if err != nil {
		return nil, fmt.Errorf("read shell preparation: %w", err)
	}
	if frame.Kind != launcherFrameShellPrepared {
		return nil, errors.New("launcher did not prepare a shell")
	}
	var prepared launcherShellPrepared
	if err := unmarshalLauncherPayload(frame.Payload, &prepared); err != nil {
		return nil, fmt.Errorf("decode shell preparation: %w", err)
	}
	if prepared.PID == 0 || prepared.Creation == 0 {
		return nil, errors.New("launcher returned incomplete shell identity")
	}
	shellHandle, err := winapi.OpenProcess(winapi.PROCESS_QUERY_LIMITED_INFORMATION, false, prepared.PID)
	if err != nil {
		return nil, fmt.Errorf("open prepared shell: %w", err)
	}
	actualShellBirth, birthErr := processCreation(shellHandle)
	if birthErr != nil || actualShellBirth != prepared.Creation {
		_ = winapi.CloseHandle(shellHandle)
		if birthErr != nil {
			return nil, fmt.Errorf("verify prepared shell creation time: %w", birthErr)
		}
		return nil, errors.New("prepared shell creation time changed")
	}
	var inJob bool
	if result, _, callErr := procIsProcessInJob.Call(uintptr(shellHandle), uintptr(job), uintptr(unsafe.Pointer(&inJob))); result == 0 {
		_ = winapi.CloseHandle(shellHandle)
		if callErr == syscall.Errno(0) {
			callErr = syscall.GetLastError()
		}
		return nil, fmt.Errorf("verify prepared shell Job membership: %w", callErr)
	}
	_ = winapi.CloseHandle(shellHandle)
	if !inJob {
		return nil, errors.New("prepared shell is not in the command Job")
	}
	started := manager.options.Now()
	var resourceClose sync.Once
	closeResources := func() {
		resourceClose.Do(func() {
			_ = pipes.control.file.Close()
			_ = pipes.stdin.file.Close()
			_ = winapi.CloseHandle(launcherInfo.Process)
			_ = winapi.CloseHandle(job)
		})
	}
	var signalToken winapi.Token
	if err := winapi.DuplicateTokenEx(token, winapi.TOKEN_ALL_ACCESS, nil, winapi.SecurityImpersonation, winapi.TokenPrimary, &signalToken); err != nil {
		// A signal helper is an optional control path.  The command itself is
		// already fully prepared; Signal falls back to the verified direct
		// console attach path if Windows refuses this duplicate.
		signalToken = 0
	}
	var signalTokenClose sync.Once
	releaseFn := func() error {
		if err := writeLauncherFrame(pipes.control.file, launcherFrame{Kind: launcherFrameRelease, Generation: pipes.generation}); err != nil {
			return fmt.Errorf("send launcher release: %w", err)
		}
		ack, err := readLauncherFrame(pipes.control.file, pipes.generation)
		if err != nil {
			return fmt.Errorf("read launcher release acknowledgement: %w", err)
		}
		if ack.Kind != launcherFrameReleased {
			return errors.New("launcher did not acknowledge release")
		}
		return nil
	}
	waitFn := func() (int32, bool, error) {
		_, waitErr := winapi.WaitForSingleObject(launcherInfo.Process, winapi.INFINITE)
		var code uint32
		if err := winapi.GetExitCodeProcess(launcherInfo.Process, &code); err != nil && waitErr == nil {
			waitErr = err
		}
		signalTokenClose.Do(func() {
			if signalToken != 0 {
				_ = signalToken.Close()
			}
		})
		closeResources()
		return int32(code), false, waitErr
	}
	killFn := func(code uint32) error {
		err := winapi.TerminateJobObject(job, code)
		return err
	}
	command := &exec.Cmd{Process: osProcess(prepared.PID)}
	process := manager.registerProcess(spec.IssueUUID, identity, command, pipes.stdin.file, pipes.stdout.file, pipes.stderr.file, started, waitFn, killFn, releaseFn, cleanup)
	process.creation = prepared.Creation
	if signalToken != 0 {
		process.signalFn = func(signalContext context.Context) (bool, error) {
			return runSignalHelper(signalContext, manager.options.ExecutablePath, signalToken, identity, prepared.PID, prepared.Creation)
		}
	}
	process.snapshotFn = func() (supervisor.ResourceSnapshot, error) {
		return queryJobSnapshot(job, manager.options.Now())
	}
	closeOnFailure = false
	launcherCreated = false
	return process, nil
}

// RunLauncher is the only entry point for --launcher.  It opens the four
// private pipes, reports its immutable identity, creates the requested shell
// suspended, and waits for the service's durable release frame before running
// any command code.
func RunLauncher(_ context.Context, channel string) error {
	generation, err := launcherGeneration(channel)
	if err != nil {
		return err
	}
	control, err := openLauncherPipe(channel, "control", winapi.GENERIC_READ|winapi.GENERIC_WRITE)
	if err != nil {
		return err
	}
	defer control.Close()
	stdin, err := openLauncherPipe(channel, "stdin", winapi.GENERIC_READ)
	if err != nil {
		return err
	}
	defer stdin.Close()
	stdout, err := openLauncherPipe(channel, "stdout", winapi.GENERIC_WRITE)
	if err != nil {
		return err
	}
	defer stdout.Close()
	stderr, err := openLauncherPipe(channel, "stderr", winapi.GENERIC_WRITE)
	if err != nil {
		return err
	}
	defer stderr.Close()
	var current winapi.Token
	err = winapi.OpenProcessToken(winapi.CurrentProcess(), winapi.TOKEN_QUERY, &current)
	if err != nil {
		return err
	}
	defer current.Close()
	user, err := current.GetTokenUser()
	if err != nil || user.User.Sid == nil {
		return errors.New("launcher token has no user SID")
	}
	sessionID, err := tokenInformationUint32(current, winapi.TokenSessionId)
	if err != nil {
		return err
	}
	creation, err := processCreation(winapi.CurrentProcess())
	if err != nil {
		return err
	}
	helloPayload, err := marshalLauncherPayload(launcherHello{PID: winapi.GetCurrentProcessId(), Creation: creation, SessionID: sessionID, Effective: user.User.Sid.String()})
	if err != nil {
		return err
	}
	if err := writeLauncherFrame(control, launcherFrame{Kind: launcherFrameHello, Generation: generation, Payload: helloPayload}); err != nil {
		return err
	}
	frame, err := readLauncherFrame(control, generation)
	if err != nil {
		return err
	}
	if frame.Kind != launcherFrameLaunch {
		return errors.New("launcher received an unexpected first command")
	}
	var request launcherRequest
	if err := unmarshalLauncherPayload(frame.Payload, &request); err != nil {
		return err
	}
	if err := ValidateWindowsExecutablePath(request.ApplicationName); err != nil || request.CommandLine == "" || !ValidAbsoluteWindowsPath(request.WorkingDirectory) || len(request.Environment) < 2 || request.Environment[len(request.Environment)-1] != 0 || request.Environment[len(request.Environment)-2] != 0 {
		return errors.New("launcher request failed validation")
	}
	if err := verifyExecutable(request.ApplicationName); err != nil {
		return err
	}
	for _, handle := range []winapi.Handle{winapi.Handle(stdin.Fd()), winapi.Handle(stdout.Fd()), winapi.Handle(stderr.Fd())} {
		if err := winapi.SetHandleInformation(handle, winapi.HANDLE_FLAG_INHERIT, winapi.HANDLE_FLAG_INHERIT); err != nil {
			return err
		}
	}
	application, err := winapi.UTF16PtrFromString(request.ApplicationName)
	if err != nil {
		return err
	}
	commandLine, err := winapi.UTF16FromString(request.CommandLine)
	if err != nil {
		return err
	}
	workingDirectory, err := winapi.UTF16PtrFromString(request.WorkingDirectory)
	if err != nil {
		return err
	}
	attributes, err := winapi.NewProcThreadAttributeList(1)
	if err != nil {
		return err
	}
	defer attributes.Delete()
	childHandles := []winapi.Handle{winapi.Handle(stdin.Fd()), winapi.Handle(stdout.Fd()), winapi.Handle(stderr.Fd())}
	if err := attributes.Update(winapi.PROC_THREAD_ATTRIBUTE_HANDLE_LIST, unsafe.Pointer(&childHandles[0]), uintptr(len(childHandles))*unsafe.Sizeof(childHandles[0])); err != nil {
		return err
	}
	startup := winapi.StartupInfoEx{StartupInfo: winapi.StartupInfo{Cb: uint32(unsafe.Sizeof(winapi.StartupInfoEx{})), Flags: winapi.STARTF_USESTDHANDLES | winapi.STARTF_USESHOWWINDOW, ShowWindow: winapi.SW_HIDE, StdInput: childHandles[0], StdOutput: childHandles[1], StdErr: childHandles[2]}}
	startup.ProcThreadAttributeList = attributes.List()
	var shellInfo winapi.ProcessInformation
	var environment *uint16
	if len(request.Environment) > 0 {
		environment = &request.Environment[0]
	}
	flags := uint32(winapi.CREATE_NEW_CONSOLE | winapi.CREATE_SUSPENDED | winapi.CREATE_UNICODE_ENVIRONMENT | winapi.EXTENDED_STARTUPINFO_PRESENT)
	if err := winapi.CreateProcess(application, &commandLine[0], nil, nil, true, flags, environment, workingDirectory, &startup.StartupInfo, &shellInfo); err != nil {
		return fmt.Errorf("create suspended shell: %w", err)
	}
	threadClosed := false
	closeThread := func() {
		if !threadClosed {
			threadClosed = true
			_ = winapi.CloseHandle(shellInfo.Thread)
		}
	}
	defer func() {
		closeThread()
		_ = winapi.CloseHandle(shellInfo.Process)
	}()
	shellCreation, err := processCreation(shellInfo.Process)
	if err != nil {
		return err
	}
	preparedPayload, err := marshalLauncherPayload(launcherShellPrepared{PID: shellInfo.ProcessId, Creation: shellCreation})
	if err != nil {
		return err
	}
	if err := writeLauncherFrame(control, launcherFrame{Kind: launcherFrameShellPrepared, Generation: generation, Payload: preparedPayload}); err != nil {
		return err
	}
	frame, err = readLauncherFrame(control, generation)
	if err != nil {
		_ = winapi.TerminateProcess(shellInfo.Process, 1)
		return err
	}
	if frame.Kind != launcherFrameRelease {
		_ = winapi.TerminateProcess(shellInfo.Process, 1)
		return errors.New("launcher release was not authorized")
	}
	if _, err := winapi.ResumeThread(shellInfo.Thread); err != nil {
		_ = winapi.TerminateProcess(shellInfo.Process, 1)
		return err
	}
	closeThread()
	if err := writeLauncherFrame(control, launcherFrame{Kind: launcherFrameReleased, Generation: generation}); err != nil {
		_ = winapi.TerminateProcess(shellInfo.Process, 1)
		return err
	}
	_, _ = winapi.WaitForSingleObject(shellInfo.Process, winapi.INFINITE)
	var exitCode uint32
	if err := winapi.GetExitCodeProcess(shellInfo.Process, &exitCode); err != nil {
		return err
	}
	winapi.ExitProcess(exitCode)
	return nil
}

const signalPipePrefix = `\\.\pipe\rvbox-signal-`

func newSignalPipe(effectiveSID string) (string, [16]byte, *os.File, error) {
	var generation [16]byte
	if effectiveSID == "" {
		return "", generation, nil, errors.New("signal pipe ACL requires an effective SID")
	}
	if _, err := winapi.StringToSid(effectiveSID); err != nil {
		return "", generation, nil, err
	}
	if _, err := io.ReadFull(cryptorand.Reader, generation[:]); err != nil {
		return "", generation, nil, err
	}
	channel := hex.EncodeToString(generation[:])
	sd, err := winapi.SecurityDescriptorFromString(fmt.Sprintf("O:SYD:(A;;GA;;;SY)(A;;GA;;;%s)", effectiveSID))
	if err != nil {
		return "", generation, nil, err
	}
	security := &winapi.SecurityAttributes{Length: uint32(unsafe.Sizeof(winapi.SecurityAttributes{})), SecurityDescriptor: sd}
	name := signalPipePrefix + channel
	namePtr, err := winapi.UTF16PtrFromString(name)
	if err != nil {
		return "", generation, nil, err
	}
	mode := uint32(winapi.PIPE_TYPE_BYTE | winapi.PIPE_READMODE_BYTE | winapi.PIPE_WAIT | winapi.PIPE_REJECT_REMOTE_CLIENTS)
	handle, err := winapi.CreateNamedPipe(namePtr, winapi.PIPE_ACCESS_DUPLEX, mode, 1, launcherPipeBuffer, launcherPipeBuffer, 0, security)
	if err != nil {
		return "", generation, nil, err
	}
	return channel, generation, os.NewFile(uintptr(handle), "rvbox-signal"), nil
}

func openSignalPipe(channel string) (*os.File, error) {
	if _, err := launcherGeneration(channel); err != nil {
		return nil, err
	}
	name, err := winapi.UTF16PtrFromString(signalPipePrefix + strings.ToLower(channel))
	if err != nil {
		return nil, err
	}
	deadline := time.Now().Add(launcherHandshakeTimeout)
	for {
		handle, openErr := winapi.CreateFile(name, winapi.GENERIC_READ|winapi.GENERIC_WRITE, 0, nil, winapi.OPEN_EXISTING, 0, 0)
		if openErr == nil {
			return os.NewFile(uintptr(handle), "rvbox-signal"), nil
		}
		if time.Now().After(deadline) {
			return nil, openErr
		}
		time.Sleep(10 * time.Millisecond)
	}
}

func runSignalHelper(ctx context.Context, executable string, token winapi.Token, identity supervisor.EffectiveIdentity, targetPID uint32, targetCreation uint64) (bool, error) {
	if executable == "" {
		var err error
		executable, err = os.Executable()
		if err != nil {
			return false, err
		}
	}
	if err := verifyExecutable(executable); err != nil {
		return false, err
	}
	serverChannel, serverGeneration, server, err := newSignalPipe(identity.UserSID)
	if err != nil {
		return false, err
	}
	defer server.Close()
	// Use the generated helper channel, not the command launcher channel. The
	// target identity is carried only after this helper's peer is verified.
	channel := serverChannel
	application, err := winapi.UTF16PtrFromString(executable)
	if err != nil {
		return false, err
	}
	command, err := BuildCommandLine([]string{executable, "--signal-helper", "--channel", channel})
	if err != nil {
		return false, err
	}
	commandUTF16, err := winapi.UTF16FromString(command)
	if err != nil {
		return false, err
	}
	startup := winapi.StartupInfo{Cb: uint32(unsafe.Sizeof(winapi.StartupInfo{}))}
	var info winapi.ProcessInformation
	flags := uint32(winapi.CREATE_NO_WINDOW | winapi.CREATE_UNICODE_ENVIRONMENT)
	if err := winapi.CreateProcessAsUser(token, application, &commandUTF16[0], nil, nil, false, flags, nil, nil, &startup, &info); err != nil {
		return false, err
	}
	defer func() {
		_ = winapi.CloseHandle(info.Process)
		_ = winapi.CloseHandle(info.Thread)
	}()
	creation, err := processCreation(info.Process)
	if err != nil {
		return false, err
	}
	if _, err := winapi.ResumeThread(info.Thread); err != nil {
		return false, err
	}
	pipe := launcherPipe{name: signalPipePrefix + channel, file: server}
	peerCtx, cancel := context.WithTimeout(ctx, launcherHandshakeTimeout)
	defer cancel()
	if err := connectLauncherPipe(peerCtx, pipe, launcherPeer{PID: info.ProcessId, Creation: creation, SessionID: identity.SessionID, UserSID: identity.UserSID}); err != nil {
		_ = winapi.TerminateProcess(info.Process, 1)
		return false, err
	}
	frame, err := readLauncherFrameContext(peerCtx, server, serverGeneration)
	if err != nil {
		return false, err
	}
	if frame.Kind != launcherFrameHello {
		return false, errors.New("signal helper did not send hello")
	}
	var hello launcherHello
	if err := unmarshalLauncherPayload(frame.Payload, &hello); err != nil {
		return false, err
	}
	if hello.PID != info.ProcessId || hello.Creation != creation || hello.SessionID != identity.SessionID || hello.Effective != identity.UserSID {
		return false, errors.New("signal helper identity mismatch")
	}
	payload, err := marshalLauncherPayload(signalHelperRequest{PID: targetPID, Creation: targetCreation, SessionID: identity.SessionID})
	if err != nil {
		return false, err
	}
	if err := writeLauncherFrame(server, launcherFrame{Kind: launcherFrameSignalRequest, Generation: serverGeneration, Payload: payload}); err != nil {
		return false, err
	}
	frame, err = readLauncherFrameContext(peerCtx, server, serverGeneration)
	if err != nil {
		return false, err
	}
	if frame.Kind != launcherFrameSignalResult {
		return false, errors.New("signal helper returned an unexpected frame")
	}
	var result signalHelperResult
	if err := unmarshalLauncherPayload(frame.Payload, &result); err != nil {
		return false, err
	}
	_, _ = winapi.WaitForSingleObject(info.Process, uint32(launcherHandshakeTimeout/time.Millisecond))
	return result.Delivered, nil
}

// RunSignalHelper verifies the target process identity supplied over its
// authenticated pipe before attaching to its private console. It never takes
// a PID from the command line and never receives a Job or stdio handle.
func RunSignalHelper(_ context.Context, channel string) error {
	generation, err := launcherGeneration(channel)
	if err != nil {
		return err
	}
	pipe, err := openSignalPipe(channel)
	if err != nil {
		return err
	}
	defer pipe.Close()
	var current winapi.Token
	if err := winapi.OpenProcessToken(winapi.CurrentProcess(), winapi.TOKEN_QUERY, &current); err != nil {
		return err
	}
	defer current.Close()
	user, err := current.GetTokenUser()
	if err != nil || user.User.Sid == nil {
		return errors.New("signal helper token has no user SID")
	}
	sessionID, err := tokenInformationUint32(current, winapi.TokenSessionId)
	if err != nil {
		return err
	}
	creation, err := processCreation(winapi.CurrentProcess())
	if err != nil {
		return err
	}
	hello, err := marshalLauncherPayload(launcherHello{PID: winapi.GetCurrentProcessId(), Creation: creation, SessionID: sessionID, Effective: user.User.Sid.String()})
	if err != nil {
		return err
	}
	if err := writeLauncherFrame(pipe, launcherFrame{Kind: launcherFrameHello, Generation: generation, Payload: hello}); err != nil {
		return err
	}
	frame, err := readLauncherFrame(pipe, generation)
	if err != nil {
		return err
	}
	if frame.Kind != launcherFrameSignalRequest {
		return errors.New("signal helper received an unexpected frame")
	}
	var request signalHelperRequest
	if err := unmarshalLauncherPayload(frame.Payload, &request); err != nil {
		return err
	}
	if request.PID == 0 || request.Creation == 0 || request.SessionID != sessionID {
		return errors.New("signal helper target identity is invalid")
	}
	target, err := winapi.OpenProcess(winapi.PROCESS_QUERY_LIMITED_INFORMATION, false, request.PID)
	if err != nil {
		return err
	}
	actualCreation, err := processCreation(target)
	if err != nil {
		_ = winapi.CloseHandle(target)
		return err
	}
	if actualCreation != request.Creation {
		_ = winapi.CloseHandle(target)
		return errors.New("signal helper target creation time mismatch")
	}
	var targetToken winapi.Token
	if err := winapi.OpenProcessToken(target, winapi.TOKEN_QUERY, &targetToken); err != nil {
		_ = winapi.CloseHandle(target)
		return err
	}
	defer targetToken.Close()
	targetUser, err := targetToken.GetTokenUser()
	if err != nil || targetUser.User.Sid == nil || targetUser.User.Sid.String() != user.User.Sid.String() {
		_ = winapi.CloseHandle(target)
		return errors.New("signal helper target token SID mismatch")
	}
	targetSession, err := tokenInformationUint32(targetToken, winapi.TokenSessionId)
	_ = winapi.CloseHandle(target)
	if err != nil || targetSession != sessionID {
		return errors.New("signal helper target session mismatch")
	}
	delivered, deliveryErr := sendControlBreak(request.PID)
	detail := "CTRL_BREAK delivered"
	if deliveryErr != nil {
		detail = deliveryErr.Error()
	}
	result, err := marshalLauncherPayload(signalHelperResult{Delivered: delivered, Detail: detail})
	if err != nil {
		return err
	}
	if err := writeLauncherFrame(pipe, launcherFrame{Kind: launcherFrameSignalResult, Generation: generation, Payload: result}); err != nil {
		return err
	}
	return nil
}