Add Win32 binding for foreground window and minimize

internal/winapi/winapi.go

@@ -0,0 +1,70 @@
+//go:build windows
+
+package winapi
+
+import (
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+var (
+	user32             = windows.NewLazySystemDLL("user32.dll")
+	procGetWindowTextW = user32.NewProc("GetWindowTextW")
+	procShowWindow     = user32.NewProc("ShowWindow")
+)
+
+// ForegroundWindow returns the current foreground window's handle (as a uintptr
+// so platform-neutral callers need not import windows), its title, and its
+// on-task class (process exe base name; see ClassFromImagePath). ok is false
+// when there is no foreground window (e.g. secure desktop / lock screen).
+func ForegroundWindow() (hwnd uintptr, title, class string, ok bool) {
+	h := windows.GetForegroundWindow()
+	if h == 0 {
+		return 0, "", "", false
+	}
+	return uintptr(h), windowTitle(h), windowClass(h), true
+}
+
+func windowTitle(h windows.HWND) string {
+	const max = 512
+	buf := make([]uint16, max)
+	n, _, _ := procGetWindowTextW.Call(
+		uintptr(h),
+		uintptr(unsafe.Pointer(&buf[0])),
+		uintptr(max),
+	)
+	return windows.UTF16ToString(buf[:n])
+}
+
+func windowClass(h windows.HWND) string {
+	var pid uint32
+	if _, err := windows.GetWindowThreadProcessId(h, &pid); err != nil || pid == 0 {
+		return ""
+	}
+	proc, err := windows.OpenProcess(windows.PROCESS_QUERY_LIMITED_INFORMATION, false, pid)
+	if err != nil {
+		return ""
+	}
+	defer windows.CloseHandle(proc)
+
+	buf := make([]uint16, windows.MAX_PATH)
+	size := uint32(len(buf))
+	if err := windows.QueryFullProcessImageName(proc, 0, &buf[0], &size); err != nil {
+		return ""
+	}
+	return ClassFromImagePath(windows.UTF16ToString(buf[:size]))
+}
+
+// MinimizeForeground minimizes the current foreground window. It returns nil
+// when nothing is focused. ShowWindow's BOOL return reports prior visibility,
+// not success, so there is nothing to error-check; minimize is best-effort by
+// the Guard contract.
+func MinimizeForeground() error {
+	h := windows.GetForegroundWindow()
+	if h == 0 {
+		return nil
+	}
+	procShowWindow.Call(uintptr(h), uintptr(windows.SW_MINIMIZE))
+	return nil
+}