#include <iostream>
#include <iomanip>
#include <vector>
#include <thread>
#include <unistd.h>
#include <algorithm>

using namespace std;

void  PiWorker(unsigned long start, unsigned long stop, long double & work);

int main(int argc, char * argv[]) {
   
     long double threads{10};
     unsigned long workSize{1'000};
     int opt;

     while((opt = getopt(argc, argv, "l:w:"))  != -1) {
        switch(opt) {
            case 'l':
                workSize = max(atoi(optarg), 100);
                break;
            case 'w':
                threads = max(atoi(optarg), 1);
                break;
            default:
                cout << argv[0] << "-l work size -w threads " << endl;
        }
     }

     vector<long double> pi(threads,0.0);
     // vector<jthread> workers;
     vector<jthread> workers(threads);
     long double finalPi{0};

     for(size_t i = 0; i < threads;  ++i) {
         //workers.emplace_back(PiWorker, i*workSize, (i+1)*workSize, ref(pi[i])); 
         workers[i] = jthread{PiWorker, i*workSize, (i+1)*workSize, ref(pi[i])}; 
     }

     for(size_t i = 0; i < workers.size(); ++i) {
         workers[i].join();
         finalPi += pi[i];
     }

     cout << "PI = "  << setprecision(20) << finalPi << endl;
     return 0;
}

void  PiWorker(unsigned long  first, unsigned long  last, long double &  work){

    cout << this_thread::get_id() << " is working on " 
         << first << " to " << last << endl;

    work = 0;

    int sign{-1};
    long double term = first * 2 + 1;
    if (first %2 == 0) {
       sign = 1;
    }

    for(unsigned long i = first; i < last; ++i) {
        work += sign * 4.0/term;
        term += 2;
        sign *= -1;
    } 
}