#include "autoopt/importer.hpp"

namespace autoopt {
std::generator<std::pair<double, double>> parse_dat_file(
    const std::filesystem::path& filename) {
  // check if file exists
  if (!std::filesystem::exists(filename)) {
    throw std::runtime_error("File does not exist: " + filename.string());
  }

  std::fstream file(filename, std::ios::in);

  std::string line;
  while (std::getline(file, line)) {
    if (line.empty() || line == "\r" || line[0] == '#') {
      continue;
    }
    std::istringstream iss(line);
    double x, y;
    iss >> x;
    for (size_t i = 1; i < 5; ++i) {
      iss >> y;  // skip unused columns
    }

    co_yield {x, -y};
  }
  co_return;
}

std::pair<std::vector<double>, std::vector<double>> parse_row(auto& iter,
                                                              auto sentinel) {
  std::vector<double> xs;
  std::vector<double> ys;
  xs.push_back((*iter).first);
  ys.push_back((*iter).second);
  ++iter;
  double last_x = xs[0];
  bool forward = last_x < (*iter).first;
  while (iter != sentinel && ((forward && last_x < (*iter).first) ||
                              (!forward && last_x > (*iter).first))) {
    xs.push_back((*iter).first);
    ys.push_back((*iter).second);
    last_x = (*iter).first;
    ++iter;
  }
  if (!forward) {
    std::reverse(xs.begin(), xs.end());
    std::reverse(ys.begin(), ys.end());
  }
  return std::make_pair(std::move(xs), std::move(ys));
}

raw_data read_data(const std::filesystem::path &filename){
  auto lines = parse_dat_file(filename);

  raw_data result;

  auto it = lines.begin();
  while (it != lines.end()) {
    auto [xs, ys] = parse_row(it, lines.end());
    if (result._xs.rows() == 0) {
      result._xs = Eigen::VectorXd(xs.size());
      std::copy(xs.begin(), xs.end(), result._xs.begin());
    }
    Eigen::VectorXd ys_vec = Eigen::VectorXd(ys.size());
    std::copy(ys.begin(), ys.end(), ys_vec.begin());
    result._yss.push_back(ys_vec);
  }

  return result;
}

}  // namespace autoopt