factory.hpp

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// Copyright (c) 2023 Petter Nilsson. MIT License. https://github.com/pettni/ezconfig
 
#pragma once
 
#include <functional>
#include <map>
#include <memory>
#include <sstream>
 
#include "global.hpp"
 
namespace ezconfig {
 
template<bool many, typename Base, typename... Args>
class GeneralFactory
{
public:
  using OutputT    = std::conditional_t<many, std::vector<std::unique_ptr<Base>>, std::unique_ptr<Base>>;
  using GeneratorT = std::function<OutputT(Args...)>;
 
  void add(const std::string & tag, GeneratorT factory)
  {
    if (m_tags.contains(tag)) { throw std::logic_error("Tag '" + tag + "' already present"); }
    m_tags[tag] = std::move(factory);
  }
 
  OutputT create(const std::string & tag, auto &&... args)
  {
    if (auto it = m_tags.find(tag); it != m_tags.end()) {
      return std::invoke(it->second, std::forward<decltype(args)>(args)...);
    } else {
      std::stringstream ss;
      ss << "Could not find tag '" << tag << "'. ";
      ss << "Available tags: [";
      for (auto i = 0u; const auto & [tag_i, f] : m_tags) {
        ss << "'" << tag_i << "'";
        if (++i < m_tags.size()) { ss << ", "; }
      }
      ss << "]";
      throw std::logic_error(ss.str());
    }
  }
 
protected:
  std::map<std::string, GeneratorT> m_tags;
};
 
template<typename Base, typename... Args>
using Factory = GeneralFactory<false, Base, Args...>;
 
template<typename Base, typename... Args>
using ManyFactory = GeneralFactory<false, Base, Args...>;
 
template<bool many, typename Base, typename... Args>
struct has_factory : public std::false_type
{};
 
template<typename Base, typename... Args>
concept Constructible = requires { has_factory<false, Base, Args...>::value == true; };
 
template<typename Base, typename... Args>
concept ManyConstructible = requires { has_factory<true, Base, Args...>::value == true; };
 
#define EZ_GENERAL_FACTORY_DECLARE(many, Base, ...)                                           \
  EZ_GLOBAL_DECLARE(ezconfig::GeneralFactory<many, Base __VA_OPT__(, ) __VA_ARGS__>);         \
  template<>                                                                                  \
  struct ezconfig::has_factory<many, Base __VA_OPT__(, ) __VA_ARGS__> : public std::true_type \
  {}
 
#define EZ_GENERAL_FACTORY_DEFINE(many, Base, ...) \
  EZ_GLOBAL_DEFINE(ezconfig::GeneralFactory<many, Base __VA_OPT__(, ) __VA_ARGS__>)
 
#define EZ_GENERAL_FACTORY_INSTANCE(many, Base, ...) \
  EZ_GLOBAL_INSTANCE(ezconfig::GeneralFactory<many, Base __VA_OPT__(, ) __VA_ARGS__>)
 
#define EZ_GENERAL_FACTORY_REGISTER(many, tag, creator, Base, ...)         \
  EZ_STATIC_INVOKE(                                                        \
    &ezconfig::GeneralFactory<many, Base __VA_OPT__(, ) __VA_ARGS__>::add, \
    EZ_GENERAL_FACTORY_INSTANCE(many, Base, __VA_ARGS__),                  \
    tag,                                                                   \
    creator)
 
#define EZ_FACTORY_DECLARE(Base, ...) EZ_GENERAL_FACTORY_DECLARE(false, Base, __VA_ARGS__)
#define EZ_FACTORY_DEFINE(Base, ...) EZ_GENERAL_FACTORY_DEFINE(false, Base, __VA_ARGS__)
#define EZ_FACTORY_INSTANCE(Base, ...) EZ_GENERAL_FACTORY_INSTANCE(false, Base, __VA_ARGS__)
#define EZ_FACTORY_REGISTER(tag, creator, Base, ...) EZ_GENERAL_FACTORY_REGISTER(false, tag, creator, Base, __VA_ARGS__)
 
}  // namespace ezconfig