Warehouse buys products from producer irregularly in bulk quantities. If the warehouse buys a lot of product units at one time the warehouse stops buying for several weeks (let's say week is a time unit). The more they buy (i.e. because of the price promotion), the farther they postpone future buying. I have time series of producer sales to warehouse but I don't know how many units leaks out of the warehouse to retailers - retail shops may also buy irregularly from the warehouse. What is the approach to model stocks of the warehouse from the producer point of view?
How many units the warehouse will buy in the next future week? How much of the current producer sales to warehouse is because of the low stocks in the preceding weeks?