//go:build windows

package compose

import (
	"context"
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"sync"
	"syscall"
	"unsafe"

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

// PROC_THREAD_ATTRIBUTE_JOB_LIST is intentionally kept here because x/sys does
// not expose this newer SDK constant yet. Supplying it to CreateProcess makes
// job ownership atomic with process creation; CREATE_SUSPENDED plus a later
// AssignProcessToJobObject is not sufficient (the parent can die in between).
const procThreadAttributeJobList = 0x0002000d

// The generic exec.Cmd path is not used on Windows: runBoundedPlatform launches
// with CreateProcess and a creation-time job-list attribute. These hooks remain
// for the platform-neutral runner's compile-time shape only.
func configureOwnedProcess(*exec.Cmd) {}
func registerOwnedProcess(*exec.Cmd) error {
	return errors.New("Windows owned processes require creation-time job ownership")
}
func releaseOwnedProcess(*exec.Cmd) {}
func terminateOwnedProcess(c *exec.Cmd) {
	if c.Process != nil {
		_ = c.Process.Kill()
	}
}

func runBoundedPlatform(ctx context.Context, runner Runner, args []string, stdin io.Reader, limits CaptureLimits) (Result, bool, error) {
	if limits.StdoutBytes < 0 || limits.StderrBytes < 0 {
		return Result{}, true, ErrOutputLimit
	}
	result, err := runBoundedWindows(ctx, runner.binary, args, stdin, limits)
	return result, true, err
}

type windowsCollector struct {
	buf      []byte
	n        int64
	overflow bool
}

func runBoundedWindows(ctx context.Context, binary string, args []string, stdin io.Reader, limits CaptureLimits) (Result, error) {
	job, err := windows.CreateJobObject(nil, nil)
	if err != nil {
		return Result{}, err
	}
	closeJob := true
	defer func() {
		if closeJob {
			windows.CloseHandle(job)
		}
	}()
	limitsInfo := windows.JOBOBJECT_EXTENDED_LIMIT_INFORMATION{}
	limitsInfo.BasicLimitInformation.LimitFlags = windows.JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE
	if _, err = windows.SetInformationJobObject(job, windows.JobObjectExtendedLimitInformation, uintptr(unsafe.Pointer(&limitsInfo)), uint32(unsafe.Sizeof(limitsInfo))); err != nil {
		return Result{}, err
	}

	stdinRead, stdinWrite, err := os.Pipe()
	if err != nil {
		return Result{}, err
	}
	stdoutRead, stdoutWrite, err := os.Pipe()
	if err != nil {
		_ = stdinRead.Close()
		_ = stdinWrite.Close()
		return Result{}, err
	}
	stderrRead, stderrWrite, err := os.Pipe()
	if err != nil {
		_ = stdinRead.Close()
		_ = stdinWrite.Close()
		_ = stdoutRead.Close()
		_ = stdoutWrite.Close()
		return Result{}, err
	}
	closeAll := func() {
		_ = stdinRead.Close()
		_ = stdinWrite.Close()
		_ = stdoutRead.Close()
		_ = stdoutWrite.Close()
		_ = stderrRead.Close()
		_ = stderrWrite.Close()
	}
	defer closeAll()
	childHandles := []windows.Handle{windows.Handle(stdinRead.Fd()), windows.Handle(stdoutWrite.Fd()), windows.Handle(stderrWrite.Fd())}
	for _, h := range childHandles {
		if err := windows.SetHandleInformation(h, windows.HANDLE_FLAG_INHERIT, windows.HANDLE_FLAG_INHERIT); err != nil {
			return Result{}, err
		}
	}
	// The attribute list limits inheritance to exactly these standard handles.
	attributes, err := windows.NewProcThreadAttributeList(2)
	if err != nil {
		return Result{}, err
	}
	defer attributes.Delete()
	jobList := []windows.Handle{job}
	if err := attributes.Update(procThreadAttributeJobList, unsafe.Pointer(&jobList[0]), unsafe.Sizeof(jobList[0])); err != nil {
		return Result{}, err
	}
	if err := attributes.Update(windows.PROC_THREAD_ATTRIBUTE_HANDLE_LIST, unsafe.Pointer(&childHandles[0]), uintptr(len(childHandles))*unsafe.Sizeof(childHandles[0])); err != nil {
		return Result{}, err
	}

	command := syscall.EscapeArg(binary)
	for _, arg := range args {
		command += " " + syscall.EscapeArg(arg)
	}
	commandLine, err := windows.UTF16FromString(command)
	if err != nil {
		return Result{}, err
	}
	startup := windows.StartupInfoEx{
		StartupInfo: windows.StartupInfo{
			Cb:        uint32(unsafe.Sizeof(windows.StartupInfoEx{})),
			Flags:     windows.STARTF_USESTDHANDLES,
			StdInput:  childHandles[0],
			StdOutput: childHandles[1],
			StdErr:    childHandles[2],
		},
		ProcThreadAttributeList: attributes.List(),
	}
	var process windows.ProcessInformation
	creationFlags := uint32(windows.CREATE_UNICODE_ENVIRONMENT | windows.CREATE_NEW_PROCESS_GROUP | windows.EXTENDED_STARTUPINFO_PRESENT)
	if err := windows.CreateProcess(nil, &commandLine[0], nil, nil, true, creationFlags, nil, nil, (*windows.StartupInfo)(unsafe.Pointer(&startup)), &process); err != nil {
		return Result{ExitCode: 127}, err
	}
	// The child owns duplicate pipe handles; parent copies use the opposite ends.
	_ = stdinRead.Close()
	_ = stdoutWrite.Close()
	_ = stderrWrite.Close()
	_ = windows.CloseHandle(process.Thread)

	var inputDone sync.WaitGroup
	inputDone.Add(1)
	go func() {
		defer inputDone.Done()
		defer stdinWrite.Close()
		if stdin != nil {
			_, _ = io.Copy(stdinWrite, stdin)
		}
	}()
	out := windowsCollector{buf: make([]byte, limits.StdoutBytes)}
	er := windowsCollector{buf: make([]byte, limits.StderrBytes)}
	overflow := make(chan struct{}, 1)
	var readers sync.WaitGroup
	readers.Add(2)
	read := func(file *os.File, maximum int64, collector *windowsCollector) {
		defer readers.Done()
		chunk := make([]byte, 32*1024)
		for {
			n, readErr := file.Read(chunk)
			if n > 0 {
				remain := maximum - collector.n
				if remain > 0 {
					take := int64(n)
					if take > remain {
						take = remain
					}
					copy(collector.buf[collector.n:collector.n+take], chunk[:take])
					collector.n += take
				}
				if int64(n) > remain {
					collector.overflow = true
					select {
					case overflow <- struct{}{}:
					default:
					}
					return
				}
			}
			if readErr != nil {
				return
			}
		}
	}
	go read(stdoutRead, limits.StdoutBytes, &out)
	go read(stderrRead, limits.StderrBytes, &er)
	waited := make(chan uint32, 1)
	go func() {
		_, waitErr := windows.WaitForSingleObject(process.Process, windows.INFINITE)
		if waitErr != nil {
			waited <- uint32(0x103)
		} else {
			var code uint32
			if windows.GetExitCodeProcess(process.Process, &code) != nil {
				code = 1
			}
			waited <- code
		}
	}()
	var exitCode uint32
	var cancelled error
	select {
	case exitCode = <-waited:
		// Closing the job handle kills any descendants before waiting on pipe readers.
		_ = windows.CloseHandle(job)
		closeJob = false
	case <-overflow:
		_ = windows.TerminateJobObject(job, 1)
		exitCode = <-waited
		_ = windows.CloseHandle(job)
		closeJob = false
	case <-ctx.Done():
		cancelled = ctx.Err()
		_ = windows.TerminateJobObject(job, 1)
		exitCode = <-waited
		_ = windows.CloseHandle(job)
		closeJob = false
	}
	_ = windows.CloseHandle(process.Process)
	_ = stdinWrite.Close()
	readers.Wait()
	inputDone.Wait()
	result := Result{Stdout: string(out.buf[:out.n]), Stderr: string(er.buf[:er.n]), ExitCode: int(exitCode)}
	if out.overflow || er.overflow {
		return result, ErrOutputLimit
	}
	if cancelled != nil {
		return result, cancelled
	}
	if exitCode == 0 {
		return result, nil
	}
	return result, fmt.Errorf("child exited with code %d", exitCode)
}