The very basic client app, not adapted for mobiles.

client/internal/services/core/mainwindow.go

@@ -0,0 +1,32 @@
+package core
+
+import (
+	"errors"
+
+	"fyne.io/fyne/v2"
+	"fyne.io/fyne/v2/container"
+)
+
+// ServiceNameMainWindow is a name for main window service.
+const ServiceNameMainWindow = "core/mainwindow"
+
+var (
+	// ErrMainWindow indicates that error appeared somewhere in main window service.
+	ErrMainWindow = errors.New("main window service")
+	// ErrMainWindowIsInvalid indicates that main window service implementation is invalid.
+	ErrMainWindowIsInvalid = errors.New("main window service implementation is invalid")
+)
+
+// MainWindow is an interface for main window service.
+type MainWindow interface {
+	// AddTab adds tab in main window.
+	AddTab(tab *container.TabItem)
+	// MainWindow returns main window instance (e.g. for using as parent with dialogs).
+	MainWindow() fyne.Window
+	// RegisterAboutWindowSysInfoHandler registers handler for System Info tab in About dialog.
+	RegisterAboutWindowSysInfoHandler(name string, hndl SysInfoHandler) error
+}
+
+// SysInfoHandler is a function signature for registering with additional system information handler for About dialog.
+// It should return valid markdown and should end with "\n".
+type SysInfoHandler func() string