#include <chrono>
#include <queue>
#include <random>
#include <string>


namespace bench {

using clock_t = std::chrono::system_clock;

struct SensorSample
{
    unsigned sensor_id;
    clock_t::time_point timestamp;
    std::string payload;
};

struct SensorReaderMockup
{
    unsigned sensor_id;
    clock_t::duration interval;
    clock_t::time_point last_sample;

    SensorSample next()
    {
        SensorSample rtrn {
                sensor_id, last_sample,
                "some payload longer than SSO" };
        last_sample += interval;
        return rtrn;
    }
};

struct SampleCompare
{
    bool operator()(const SensorSample& left,
                    const SensorSample& right) const noexcept
    { return left.timestamp > right.timestamp; }
};

using min_heap_t = std::priority_queue<
        SensorSample, std::vector<SensorSample>, SampleCompare>;


void run_heap(SensorReaderMockup* sensor_states, unsigned sensors,
              int events)
{
    min_heap_t heap;
    /*
     * Read first sample of each sensor
     */
    for(std::size_t i = 0; i < sensors; ++i)
        heap.push(sensor_states[i].next());
    for(int i = 0; i < events; ++i) {
        /*
         * Retrieve oldest sample for transfer to output
         */
        SensorSample oldest = std::move(heap.top());
        heap.pop();
        /*
         * Read next sample from this particular sensor.
         * Real code would obviously have to check whether sensor is at
         * end-of-file
         */
        heap.push(sensor_states[oldest.sensor_id].next());
    }
}

/**
 * Initializes sensors with pseudo-random sampling periods
 */
std::vector<SensorReaderMockup> init_state(unsigned sensors)
{
    std::vector<SensorReaderMockup> rtrn;
    rtrn.reserve(sensors);
    std::default_random_engine rng;
    std::uniform_int_distribution<int> distr {1, 100};
    for(unsigned i = 0; i < sensors; ++i) {
        clock_t::duration interval {distr(rng)};
        clock_t::time_point last_sample = clock_t::time_point{} + interval;
        rtrn.push_back(SensorReaderMockup{i, interval, last_sample});
    }
    return rtrn;
}

} // namespace bench


int main()
{
    using namespace bench;
    unsigned sensors = 60'000;
    int events = 100'000'000;
    std::vector<SensorReaderMockup> sensor_states = init_state(sensors);
    run_heap(sensor_states.data(), sensors, events);
}