std::size_t shop::getBatchCost (const std::vector <std::pair<std::size_t, std::size_t>>& batch) const {
    
    std::map <std::pair<size_t, std::string>, std::pair <std::size_t, std::size_t>>::const_iterator prodIt = products.begin();
    std::vector <std::pair<std::size_t, std::size_t>>::const_iterator batchIt = batch.begin();


    std::size_t totalSum = 0;
    while (batchIt != batch.end()) {
        while (prodIt != products.end()) {
            if (prodIt->first.first == batchIt->first) {
                if (batchIt->second > prodIt->second.first) {
                    throw std::runtime_error ("The amount of vegetables less than requested!");
                } else {
                    totalSum += prodIt->second.second * batchIt->second;
                }
            }
            prodIt++;
        }
        batchIt++;
    }
    return totalSum;
}

std::size_t getProdCost (const std::size_t prodId) const;