calculate_need_for_ps

/**
 * calculates how much a productionsite of type \arg bo is needed inside it's
 * economy. \arg prio is initial value for this calculation
 *
 * \returns the calculated priority
 */
int32_t DefaultAI::calculate_need_for_ps(BuildingObserver & bo, int32_t prio)
{
    // some randomness to avoid that defaultAI is building always
    // the same (always == another game but same map with
    // defaultAI on same coords)
    prio += time(nullptr) % 3 - 1;

    // check if current economy can supply enough material for
    // production.
    for (uint32_t k = 0; k < bo.inputs.size(); ++k) {
        prio += 2 * wares.at(bo.inputs.at(k)).producers;
        prio -= wares.at(bo.inputs.at(k)).consumers;
    }
    if (bo.inputs.empty())
        prio += 4;

    int32_t output_prio = 0;
    for (uint32_t k = 0; k < bo.outputs.size(); ++k) {
        WareObserver & wo = wares.at(bo.outputs.at(k));
        if (wo.consumers > 0) {
            output_prio += wo.preciousness;
            output_prio += wo.consumers * 2;
            output_prio -= wo.producers * 2;
            if (bo.total_count() == 0)
                output_prio += 10; // add a big bonus
        }
    }
    if (bo.outputs.size() > 1)
        output_prio = static_cast<int32_t>
            (ceil(output_prio / sqrt(static_cast<double>(bo.outputs.size()))));
    prio += 2 * output_prio;

    // If building consumes some wares, multiply with current statistics of all
    // other buildings of this type to avoid constructing buildings where already
    // some are running on low resources.
    // Else at least add a part of the stats t the calculation.
    if (!bo.inputs.empty()) {
        prio *= bo.current_stats;
        prio /= 100;
    } else
        prio = ((prio * bo.current_stats) / 100) + (prio / 2);

    return prio;
}