What are the conditions confess, revenue from the sale of goods, as well as resulting from contracts to provide services?

in sale of goods we recognize income immediatly when control is transferred.but on providing services we recognize revenue when service is provided or servicr is completed.for example resturant offer room for a day and receive cash of50.it is not income it is treated as liability.after completing service( when day ends) then revenue should be recognized.as per IAS-18