Strategy.hpp

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#pragma once
 
#include <map>
#include <memory>
#include <stdexcept>
#include <string>
 
#include <nlohmann/json.hpp>

template<typename Derived> struct Strategy {
  using Ptr = std::shared_ptr<Derived>;

  using Factory = Ptr (*)(nlohmann::json const&);
 
  virtual ~Strategy() = default;

  virtual void to_json(nlohmann::json& j) const = 0;

  virtual std::string display_name() const = 0;

  static bool register_strategy(std::string const& name, Factory factory) {
    registry()[name] = factory;
    return true;
  }

  static Ptr from_json(nlohmann::json const& j) {
    auto name = j.at("name").get<std::string>();
    auto& reg = registry();
    auto it   = reg.find(name);
 
    if (it == reg.end())
      throw std::runtime_error("Unknown strategy: " + name);
 
    return it->second(j);
  }
 
private:
  static std::map<std::string, Factory>& registry() {
    static std::map<std::string, Factory> r;
    return r;
  }
};

#define PPFOREST2_REGISTER_STRATEGY(StrategyBase, name) \
  inline static const bool registered_ = StrategyBase::register_strategy(name, from_json);