Stock Control Application - Make changes to the backend

Hello, we are rewriting a java based web application to control stock, sales, purchases and inventories of a Pharmacy. We would like help to implement part of the logic of the stock control. The features we need are: - Be able to sell packages or units; - Support multiple warehouses; - Be able to inform stock quantities for each product on each warehouse; - Support automatic price change when one batch is depleted; - Be able to query the batches that will expire soon; - Be able to sell when calculations indicate that there is no stock left for the product (purchase of the product was done but not entered on the application yet) and compensate when the purchase of the product is entered on the application; - Allow corrections of the purchases while keeping the calculations correct; - Allow inventories; - Allow transfer of batches from one warehouse to another, the full batch or part of it; - Allow removal of expired products; We already have a class model in place and project implemented. The bidder will study this class model and propose changes if necessary. We would like the bidder to provide the necessary code changes and JUnit tests to prove that everything is working well. We are using Java, JUnit 4, DBUnit, Spring and Hibernate 4 as a JPA2.1 implentation. We are also using drools but this is optional, we are open to convert everything to java is necessary.