#include <iostream>
#include <string>
#include <random>
#include <vector>
//Command-line parsing
#include <CLI11.hpp>

//Image filtering and I/O
#define STB_IMAGE_IMPLEMENTATION
#include <stb_image.h>
#define STB_IMAGE_WRITE_IMPLEMENTATION
#include <stb_image_write.h>

//Global flag to silent verbose messages
bool silent;
bool test_energy;


/** e_1 energy */
std::vector<unsigned char> energy_e1(unsigned char* source, int width, int height, int nbChannels) {
  std::vector<unsigned char> energy(width*height);

  for (auto i=0; i < width*height; i++) { energy[i] = 0; }

  for(auto i = 0 ; i < width ; ++i) {
    for(auto j = 0; j < height; ++j) {
      auto indexPixel = nbChannels*(width*j+i);
      auto indexPixel_up    = (j-1 > 0)      ? nbChannels*(width*(j-1)+i) : indexPixel;
      auto indexPixel_down  = (j+1 < height) ? nbChannels*(width*(j+1)+i) : indexPixel;
      auto indexPixel_left  = (i-1 > 0)      ? nbChannels*(width*j+(i-1)) : indexPixel;
      auto indexPixel_right = (i+1 < width)  ? nbChannels*(width*j+(i+1)) : indexPixel;

      for (auto ch=0; ch < nbChannels; ch++) {
        energy[width*j+i] += (
            fabs((float)source[indexPixel_up+ch] - source[indexPixel+ch])
            +fabs((float)source[indexPixel_down+ch] - source[indexPixel+ch])
            +fabs((float)source[indexPixel_left+ch] - source[indexPixel+ch])
            +fabs((float)source[indexPixel_right+ch] - source[indexPixel+ch])
        )/(nbChannels*4);
      }
    }
  }

  return energy;
}


int main(int argc, char **argv) {
  CLI::App app{"seam-carving"};
  std::string sourceImage;
  app.add_option("-s,--source", sourceImage, "Source image")->required()->check(CLI::ExistingFile);;
  std::string outputImage= "output.png";
  app.add_option("-o,--output", outputImage, "Output image")->required();
  silent = false;
  app.add_flag("--silent", silent, "No verbose messages");
  test_energy = false;
  app.add_flag("--test-energy", test_energy, "Don't resize image, just try the specified energy function");
  CLI11_PARSE(app, argc, argv);

  //Image loading
  int width, height, nbChannels;
  unsigned char *source = stbi_load(sourceImage.c_str(), &width, &height, &nbChannels, 0);

  if (nbChannels < 3) { // TODO : really ?
    std::cout<< "Input images must be RGB images."<<std::endl;
    exit(1);
  }

  int outChannels = nbChannels;
  std::vector<unsigned char> output;

  if (test_energy) {
    outChannels = 1;
    output = energy_e1(source, width, height, nbChannels);
  } else {
    std::cout <<"Not implemented" << std::endl;
    exit(1);
  }

  //Final export
  if (!silent) std::cout<<"Exporting.."<<std::endl;
  int errcode = stbi_write_png(outputImage.c_str(), width, height, outChannels, output.data(), outChannels*width);
  if (!errcode) {
    std::cout<<"Error while exporting the resulting image."<<std::endl;
    exit(errcode);
  }

  stbi_image_free(source);
  exit(0);
}