#include "stb_image.h"  //Put stb_image.h from  https://github.com/nothings/stb/blob/master/stb_image.h along side this file in the same dir
            //compile with g++ -Os getdot.cpp -o getdot.   Run with ./getdot <filename>
#include <queue>
#include <iostream>
#include <string>
#include <ctime>
struct Image
{
    int width;
    int height;
    unsigned char* data;
    Image(const std::string& filename)
    {
        int n;
        data=stbi_load(filename.c_str(),&width,&height,&n,3);
    }
    ~Image()
    {
        stbi_free(data);
    }
};

struct Pixel
{
    int x,y,score;
    Pixel(int tx,int ty,int tr,int tg,int tb):
        x(tx),y(ty),score(tr-(tg+tb))
    {}
    bool operator<(const Pixel& o) const
    {
        return score >= o.score;//we want the heap top to be the lowest one on top, so invert
    }
};

Pixel getDot(const Image& i)
{
    std::priority_queue<Pixel> toppixels;
    for(size_t y=0;y < i.height;y++)
    {
        for(size_t x=0;x < i.width;x++)
        {
            size_t index=y*width+x;
            unsigned char *pixel_data=i.data+3*index;
            toppixels.emplace(x,y,pixel_data[0],pixel_data[1],pixel_data[2]);
            if(toppixels.size() >= 10)
            {
                toppixels.pop();
            }
        }
    }

    Pixel avg(0,0,0,0,0);
    size_t n=toppixels.size();
    while(!toppixels.empty())
    {
        Pixel c=toppixels.pop();
        avg.x+=c.x;
        avg.y+=c.y;
        avg.score+=c.score;
    }
    avg.x/=n;
    avg.y/=n;
    avg.score/=n;

    return avg;
}

int main(int argc,char** argv)
{
    Image image_to_load(argv[1]);//the filename is the first argument

    clock_t orig=clock();
    Pixel center=getDot(image_to_load);
    clock_t after=clock();

    clock_t deltams=(after-orig)*1000;

    std::cout << "The pixel center is at (" << avg.x << "," << avg.y << ")" << std::endl;
    std::cout << "Finding it took approximately " << deltams/CLOCKS_PER_SEC << " ms" << std::endl;

    return 0;
}