Excel VBA : accounting calculation tool

The tool will receive an Excel file containing invoices, one invoice per line, and a parameter sheet which will include variables for calculations. Calculation rules are fixed and hard-coded, parameters will be supplied via an external sheet. The tool will have to select all the invoices, to cumulate them by date, client or other criteria, to launch calculations based on a subset of criteria (e.g. X in column A and Y in column B) and to display them in a specified format that will be printed out. The macro to be developed will be properly commented and clean. No "macro record" operation will be accepted. No "cells" but "range", no "select". I need a proper macro, that's it. Controls of coherency must be implemented: grand total, checks on columns... The project is easy for a good developer, since all the calculation logic will be very easy to implement and we cold do that by ourselves. So, you need to set up a proper and safe macro environment, that's it. We will not answer to developers without rating or with a poor rating. We will ask for an example of Excel VBA code beforehand.