Additional modules are integrated with POS logic using events. For this purpose, there are special interfaces in POS that allow such communication. Each interface has its “internal” counterpart. The base interface defines service methods for the needs of communication with external services. The “internal” service defines events through which communication is carried out.

The base interface is used in viewModels in POS.

The internal interface is used in external modules.

The current interfaces are:

• IDeviceEventService and IDeviceEventInternalService (handling of the drawer)
• IDocumentEventService and IDocumentEventInternalService (printing of documents on a receipt printer)
• IFiscalPrinterEventService and IFiscalPrinterEventInternalService (printouts made for the purposes of electronic payments on a receipt printer)
• IPaymentEventService and IPaymentEventInternalService (electronic payments)
• ISessionEventService and ISessionEventInternalService (cash register reports and electronic payment reports)