exercise6.cpp

#include "city.h"
#include "country.h"
#include "world-util.h"

#include <map>
#include <iostream>
#include <string>
#include <memory>
#include <numeric>

using namespace std;
using namespace world;

map<int, shared_ptr<city>> cities;
map<string, shared_ptr<country>> countries;

template<class T>
struct statistics {
    T minimum;
    T maximum;
    double sum;
    int numberOfSamples;

    statistics() : sum(0), numberOfSamples(0) {}

    [[maybe_unused]] explicit statistics(T value) : sum(value), numberOfSamples(1), minimum(value), maximum(value) {}

    [[nodiscard]] double average() const {
        if (numberOfSamples == 0) return 0.0;
        return sum / numberOfSamples;
    }
};

template<class T>
ostream &operator<<(ostream &out, const statistics<T> &stats) {
    out << "statistics [ number of samples= " << stats.numberOfSamples
        << ", minimum=" << stats.minimum
        << ", maximum=" << stats.maximum
        << ", sum=" << stats.sum
        << ", average=" << stats.average()
        << " ]";
    return out;
}

using statistics_int = statistics<int>;
using statistics_int_ptr = shared_ptr<statistics_int>;

int main() {
    create_world();

    // Find the min, the max, and the average population at each continent
    auto statisticsReducer = [](auto &&continentStatistics, auto &entry) {
        auto country = entry.second;
        auto continent = country->continent;
        auto continentStatisticsIterator = continentStatistics.find(continent);
        if (continentStatisticsIterator == continentStatistics.end())
            continentStatistics[continent] = make_shared<statistics_int>(statistics_int(country->population));
        else {
            auto continentStat = continentStatisticsIterator->second;
            auto countryPopulation = country->population;
            if (continentStat->minimum > countryPopulation) continentStat->minimum = countryPopulation;
            if (continentStat->maximum < countryPopulation) continentStat->maximum = countryPopulation;
            continentStat->sum += countryPopulation;
            continentStat->numberOfSamples++;
        }
        return continentStatistics;
    };

    auto continentStatistics = accumulate(countries.begin(), countries.end(), map<string, statistics_int_ptr>(),
                                          statisticsReducer);

    for (auto &entry: continentStatistics) {
        cout << entry.first << ": " << *(entry.second) << endl;
    }
    return 0;
}