terminal/backend_windows.go

//go:build windows

package terminal

import (
	"fmt"
	"os"
	"time"

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

const escapeTimeoutMs = 10

type windowsBackend struct {
	stdin  windows.Handle
	stdout windows.Handle

	oldStdinMode  uint32
	oldStdoutMode uint32
	oldInputCP    uint32
	oldOutputCP   uint32

	resizeStopCh chan struct{}
	resizeDoneCh chan struct{}
}

func newBackend() Backend {
	return &windowsBackend{
		stdin:  windows.Handle(os.Stdin.Fd()),
		stdout: windows.Handle(os.Stdout.Fd()),
	}
}

func (b *windowsBackend) Init() error {
	if os.Getenv("WT_SESSION") == "" && os.Getenv("WT_PROFILE_ID") == "" {
		return fmt.Errorf("Windows Terminal required: WT_SESSION unset; conhost lacks alt screen")
	}

	if err := windows.GetConsoleMode(b.stdin, &b.oldStdinMode); err != nil {
		return fmt.Errorf("GetConsoleMode stdin: %w", err)
	}
	if err := windows.GetConsoleMode(b.stdout, &b.oldStdoutMode); err != nil {
		return fmt.Errorf("GetConsoleMode stdout: %w", err)
	}
	b.oldInputCP, _ = windows.GetConsoleCP()
	b.oldOutputCP, _ = windows.GetConsoleOutputCP()

	stdinMode := uint32(windows.ENABLE_MOUSE_INPUT |
		windows.ENABLE_EXTENDED_FLAGS |
		windows.ENABLE_VIRTUAL_TERMINAL_INPUT)
	if err := windows.SetConsoleMode(b.stdin, stdinMode); err != nil {
		return fmt.Errorf("SetConsoleMode stdin: %w", err)
	}

	stdoutMode := uint32(windows.ENABLE_PROCESSED_OUTPUT |
		windows.ENABLE_VIRTUAL_TERMINAL_PROCESSING |
		windows.DISABLE_NEWLINE_AUTO_RETURN)
	if err := windows.SetConsoleMode(b.stdout, stdoutMode); err != nil {
		windows.SetConsoleMode(b.stdin, b.oldStdinMode)
		return fmt.Errorf("SetConsoleMode stdout: %w", err)
	}

	windows.SetConsoleCP(65001)
	windows.SetConsoleOutputCP(65001)

	return nil
}

func (b *windowsBackend) Fini() {
	if b.resizeStopCh != nil {
		close(b.resizeStopCh)
		<-b.resizeDoneCh
		b.resizeStopCh = nil
	}
	if b.oldStdinMode != 0 {
		windows.SetConsoleMode(b.stdin, b.oldStdinMode)
	}
	if b.oldStdoutMode != 0 {
		windows.SetConsoleMode(b.stdout, b.oldStdoutMode)
	}
	if b.oldInputCP != 0 {
		windows.SetConsoleCP(b.oldInputCP)
	}
	if b.oldOutputCP != 0 {
		windows.SetConsoleOutputCP(b.oldOutputCP)
	}
}

func (b *windowsBackend) Size() (int, int) {
	var info windows.ConsoleScreenBufferInfo
	if err := windows.GetConsoleScreenBufferInfo(b.stdout, &info); err != nil {
		return 80, 24
	}
	w := int(info.Window.Right-info.Window.Left) + 1
	h := int(info.Window.Bottom-info.Window.Top) + 1
	if w < 1 {
		w = 80
	}
	if h < 1 {
		h = 24
	}
	return w, h
}

func (b *windowsBackend) Write(p []byte) error {
	var written uint32
	return windows.WriteFile(b.stdout, p, &written, nil)
}

func (b *windowsBackend) Read(stopCh <-chan struct{}) ([]byte, error) {
	buf := make([]byte, 256)
	for {
		select {
		case <-stopCh:
			return nil, nil
		default:
		}

		ev, err := windows.WaitForSingleObject(b.stdin, uint32(escapeTimeoutMs))
		if err != nil {
			return nil, fmt.Errorf("WaitForSingleObject: %w", err)
		}
		if ev == windows.WAIT_TIMEOUT {
			// Mirrors unix poll timeout: lets readLoop emit pending standalone ESC
			return nil, nil
		}

		var n uint32
		if err := windows.ReadFile(b.stdin, buf, &n, nil); err != nil {
			return nil, fmt.Errorf("ReadFile: %w", err)
		}
		if n == 0 {
			// VTP consumed a non-keyboard record (e.g. focus event) producing no bytes
			return nil, nil
		}

		ret := make([]byte, n)
		copy(ret, buf[:n])
		return ret, nil
	}
}

func (b *windowsBackend) SetResizeHandler(handler func(int, int)) {
	b.resizeStopCh = make(chan struct{})
	b.resizeDoneCh = make(chan struct{})

	go func() {
		defer close(b.resizeDoneCh)
		ticker := time.NewTicker(100 * time.Millisecond)
		defer ticker.Stop()
		w, h := b.Size()
		for {
			select {
			case <-b.resizeStopCh:
				return
			case <-ticker.C:
				nw, nh := b.Size()
				if nw != w || nh != h {
					w, h = nw, nh
					handler(w, h)
				}
			}
		}
	}()
}