#define _USE_MATH_DEFINES
#include <cmath>
#include <memory>
#include <unordered_map>

#include "openmc/particle.h"
#include "openmc/random_lcg.h"
#include "openmc/source.h"

class RingSource : public openmc::Source {
public:
  RingSource(double radius, double energy) : radius_(radius), energy_(energy) {}

  // Defines a function that can create a unique pointer to a new instance of
  // this class by extracting the parameters from the provided string.
  static std::unique_ptr<RingSource> from_string(std::string parameters)
  {
    std::unordered_map<std::string, std::string> parameter_mapping;

    std::stringstream ss(parameters);
    std::string parameter;
    while (std::getline(ss, parameter, ',')) {
      parameter.erase(0, parameter.find_first_not_of(' '));
      std::string key = parameter.substr(0, parameter.find_first_of('='));
      std::string value =
        parameter.substr(parameter.find_first_of('=') + 1, parameter.length());
      parameter_mapping[key] = value;
    }

    double radius = std::stod(parameter_mapping["radius"]);
    double energy = std::stod(parameter_mapping["energy"]);
    return std::make_unique<RingSource>(radius, energy);
  }

  // Samples from an instance of this class.
  openmc::SourceSite sample(uint64_t* seed) const
  {
    openmc::SourceSite particle;
    // particle type
    particle.particle = openmc::ParticleType::neutron();
    // position
    double angle = 2.0 * M_PI * openmc::prn(seed);
    double radius = this->radius_;
    particle.r.x = radius * std::cos(angle);
    particle.r.y = radius * std::sin(angle);
    particle.r.z = 0.0;
    // angle
    particle.u = {1.0, 0.0, 0.0};
    particle.E = this->energy_;

    return particle;
  }

private:
  double radius_;
  double energy_;
};

// A function to create a unique pointer to an instance of this class when
// generated via a plugin call using dlopen/dlsym. You must have external C
// linkage here otherwise dlopen will not find the file
extern "C" std::unique_ptr<RingSource> openmc_create_source(
  std::string parameters)
{
  return RingSource::from_string(parameters);
}