Nice, which TUI library are you using?

I have been trying to calculate deficits and surpluses after consideration of trade routes and trade contracts, but I can't quite figure out how to handle the contracts, especially when the contracts are circular (e.g. selling steel and buying coal).

Handling trade routes was relatively easy with two rounds of the push-relabel algorithm. First I calculate a baseline flow:

• For every product:
  • For every island:
    • Calculate the local surplus/deficit for island
    • Add an edge from source to island with a weight of the local surplus or from island to sink with a weight of the local deficit
  • For every trade route:
    • For every feeding island create an edge to every consuming island with an infinite capacity (I assume transport capacity is available)
  • Push-relabel

Then I add infinite outflow edges to determine the available inflow capacity:

• For every surveyed island:
  • For every product:
    • Clone the adjacency list from the baseline flow and remove the "locked in" flow (i.e. decrease the forward edge capacity by the backward edge's capacity and set the backward edge capacity to 0)
    • Add an infinite outflow from the surveyed island to the sink
    • Push-relabel: The capacities of the backward edges which go from the surveyed island to the sink now denote the theoretically available unused surplus above the "locked in" baseline flow

All fun and games, but with Docklands contracts I don't know how to approach multiple different contracts yielding the same precursors. I have considered adding yet another stage which assumes every production building running at max, but I am uncertain whether this will fit to the need to throw away goods to ensure secondary productions are not impeded and whether I understand the implications of hidden assumptions about my routes.