According to the Adobe Commerce documentation, the Source Selection Interface is the main interface for implementing custom source selection algorithms. The interface defines a method called execute(), which takes a list of items to be shipped and a stock ID as parameters, and returns a SourceSelectionResultInterface object, which contains the recommended sources and quantities for each item. The Architect can create a new class that implements this interface and provides the logic for finding the lowest-cost warehouse that is open for each item. The Architect can then register the new class as an option for the source selection algorithm in the di.xml file of the custom module.

References:

Source Selection Algorithm | Adobe Commerce Developer Guide

Source Selection Interface | Adobe Commerce Developer Guide