roguish/tser.hpp

// Licensed under the Boost License <https://opensource.org/licenses/BSL-1.0>.
// SPDX-License-Identifier: BSL-1.0
#pragma once
#include <array>
#include <ostream>
#include <cstring>
#include <string>
#include <string_view>
#include <type_traits>
#include <tuple>

namespace tser{
  //implementation details for C++20 is_detected
  namespace detail {
    struct ns {
      ~ns() = delete;
      ns(ns const&) = delete;
    };

    template <class Default, class AlwaysVoid, template<class...> class Op, class... Args>
      struct detector {
        using value_t = std::false_type;
        using type = Default;
      };

    template <class Default, template<class...> class Op, class... Args>
      struct detector<Default, std::void_t<Op<Args...>>, Op, Args...> {
        using value_t = std::true_type;
        using type = Op<Args...>;
      };

    template<class T>
      struct is_array : std::is_array<T> {};

    template<template<typename, size_t> class TArray, typename T, size_t N>
      struct is_array<TArray<T, N>> : std::true_type {};

    constexpr size_t n_args(char const* c, size_t nargs = 1) {
      for (; *c; ++c) if (*c == ',') ++nargs;
      return nargs;
    }

    constexpr size_t str_size(char const* c, size_t strSize = 1) {
      for (; *c; ++c) ++strSize;
      return strSize;
    }
  }

  // we need a bunch of template metaprogramming for being able to differentiate between different types
  template <template<class...> class Op, class... Args>
    constexpr bool is_detected_v = detail::detector<detail::ns, void, Op, Args...>::value_t::value;

  class BinaryArchive;
  template<class T> using has_begin_t = decltype(*std::begin(std::declval<T>()));

  template<class T> using has_members_t = decltype(std::declval<T>().members());

  template<class T> using has_smaller_t = decltype(std::declval<T>() < std::declval<T>());

  template<class T> using has_equal_t = decltype(std::declval<T>() == std::declval<T>());

  template<class T> using has_nequal_t = decltype(std::declval<T>() != std::declval<T>());

  template<class T> using has_outstream_op_t = decltype(std::declval<std::ostream>() << std::declval<T>());

  template<class T> using has_tuple_t = std::tuple_element_t<0, T>;

  template<class T> using has_optional_t = decltype(std::declval<T>().has_value());

  template<class T> using has_element_t = typename T::element_type;

  template<class T> using has_mapped_t = typename T::mapped_type;

  template<class T> using has_custom_save_t = decltype(std::declval<T>().save(std::declval<BinaryArchive&>()));

  template<class T> using has_free_save_t = decltype(std::declval<const T&>() << std::declval<BinaryArchive&>());

  template<class T> constexpr bool is_container_v = is_detected_v<has_begin_t, T>;

  template<class T> constexpr bool is_tuple_v = is_detected_v<has_tuple_t, T>;

  template<class T> constexpr bool is_tser_t_v = is_detected_v<has_members_t, T>;

  template<class T> constexpr bool is_pointer_like_v = std::is_pointer_v<T> || is_detected_v<has_element_t, T> || is_detected_v<has_optional_t, T>;

  //implementation of the recursive json printing
  template<typename T>
    constexpr inline decltype(auto) print(std::ostream& os, T&& val) {
      using V = std::decay_t<T>;
      if constexpr (std::is_constructible_v<std::string, T> || std::is_same_v<V, char>) {
        os << "\"" << val << "\"";
      } else if constexpr (is_container_v<V>) {
        size_t i = 0;
        os << "\n[";

        for (auto& elem : val) {
          os << (i++ == 0 ? "" : ",") << tser::print(os, elem);
        }

        os << "]\n";
      } else if constexpr (is_tser_t_v<V> && !is_detected_v<has_outstream_op_t, V>) {

        auto pMem = [&](auto& ... memberVal) {
          size_t i = 0;
          (((os << (i != 0 ? ", " : "") << '\"'), os << V::_memberNames[i++] << "\" : " << tser::print(os, memberVal)), ...);
        };

        os << "{ \"" << V::_typeName << "\": {"; std::apply(pMem, val.members()); os << "}}\n";

      } else if constexpr (std::is_enum_v<V> &&! is_detected_v<has_outstream_op_t, V>) {
        os << tser::print(os, static_cast<std::underlying_type_t<V>>(val));
      } else if constexpr (is_tuple_v<V> && !is_detected_v<has_outstream_op_t, V>) {
        std::apply([&](auto& ... t) {
            int i = 0;
            os << "{";
            (((i++ != 0 ? os << ", " : os),
              tser::print(os, t)), ...); // WTF
            os << "}";
            }, val);
      } else if constexpr (is_pointer_like_v<V>) {
        os << (val ? (os << (tser::print(os, *val)), "") : "null");
      } else {
        os << val;
      }

      return "";
    }

  class BinaryArchive {
    std::string m_bytes = std::string(1024, '\0');
    size_t m_bufferSize = 0, m_readOffset = 0;

    public:
    explicit BinaryArchive(const size_t initialSize = 1024) : m_bytes(initialSize, '\0') {}

    template<typename T>
      explicit BinaryArchive(const T& t) { save(t); }

    template<typename T>
      void save(const T& t) {
        if constexpr (is_detected_v<has_free_save_t, T>) {
          operator<<(t,*this);
        } else if constexpr (is_detected_v<has_custom_save_t, T>) {
          t.save(*this);
        } else if constexpr(is_tser_t_v<T>) {
          std::apply([&](auto& ... mVal) { (save(mVal), ...); }, t.members());
        } else if constexpr(is_tuple_v<T>) {
          std::apply([&](auto& ... tVal) { (save(tVal), ...); }, t);
        } else if constexpr (is_pointer_like_v<T>) {
          save(static_cast<bool>(t));
          if (t)
            save(*t);
        } else if constexpr (is_container_v<T>) {
          if constexpr (!detail::is_array<T>::value) {
            save(t.size());
          }

          for (auto& val : t) save(val);
        } else {
          if (m_bufferSize + sizeof(T) + sizeof(T) / 4 > m_bytes.size()) {
            m_bytes.resize((m_bufferSize + sizeof(T)) * 2);
          }

          std::memcpy(m_bytes.data() + m_bufferSize, std::addressof(t), sizeof(T));
          m_bufferSize += sizeof(T);
        }
      }

    template<typename T>
      void load(T& t) {
        using V = std::decay_t<T>;
        if constexpr (is_detected_v<has_free_save_t, V>) {
          operator>>(t, *this);
        } else if constexpr (is_detected_v<has_custom_save_t, T>) {
          t.load(*this);
        } else if constexpr (is_tser_t_v<T>) {
          std::apply([&](auto& ... mVal) { (load(mVal), ...); }, t.members());
        } else if constexpr (is_tuple_v<V>) {
          std::apply([&](auto& ... tVal) { (load(tVal), ...); }, t);
        } else if constexpr (is_pointer_like_v<T>) {
          if constexpr (std::is_pointer_v<T>) {
            t = load<bool>() ? (t = new std::remove_pointer_t<T>(), load(*t), t) : nullptr;
          } else if constexpr (is_detected_v<has_optional_t, T>) {
            t = load<bool>() ? T(load<typename V::value_type>()) : T();
          } else { //smart pointer
            t = T(load<has_element_t<V>*>());
          }
        } else if constexpr (is_container_v<T>) {
          if constexpr (!detail::is_array<T>::value) {
            const auto size = load<decltype(t.size())>();
            using VT = typename V::value_type;
            for (size_t i = 0; i < size; ++i) {
              if constexpr (!is_detected_v<has_mapped_t, V>) {
                t.insert(t.end(), load<VT>());
              } else {
                //we have to special case map, because of the const key
                t.emplace(VT{ load<typename V::key_type>(), load<typename V::mapped_type>() });
              }
            }
          } else {
            for (auto& val : t) load(val);
          }
        } else {
          std::memcpy(&t, m_bytes.data() + m_readOffset, sizeof(T));
          m_readOffset += sizeof(T);
        }
      }

    template<typename T>
      T load() {
        std::remove_const_t<T> t{}; load(t); return t;
      }

    template<typename T>
      friend BinaryArchive& operator<<(BinaryArchive& ba, const T& t) {
        ba.save(t); return ba;
      }

    template<typename T>
      friend BinaryArchive& operator>>(BinaryArchive& ba, T& t) {
        ba.load(t); return ba;
      }

    void reset() {
      m_bufferSize = 0;
      m_readOffset = 0;
    }

    void initialize(std::string_view str) {
      m_bytes = str;
      m_bufferSize = str.size();
      m_readOffset = 0;
    }

    std::string_view get_buffer() const {
      return std::string_view(m_bytes.data(), m_bufferSize);
    }

  };

  template<class Base, typename Derived>
    std::conditional_t<std::is_const_v<Derived>, const Base, Base>& base(Derived* thisPtr) { return *thisPtr; }

  template<typename T>
    auto load(std::string_view encoded) { BinaryArchive ba(encoded); return ba.load<T>(); }
}

//this macro defines printing, serialisation and comparision operators (==,!=,<) for custom types
#define DEFINE_SERIALIZABLE(Type, ...) \
inline decltype(auto) members() const { return std::tie(__VA_ARGS__); } \
inline decltype(auto) members() { return std::tie(__VA_ARGS__); }  \
static constexpr std::array<char, tser::detail::str_size(#__VA_ARGS__)> _memberNameData = [](){ \
std::array<char, tser::detail::str_size(#__VA_ARGS__)> chars{'\0'}; size_t _idx = 0; constexpr auto* ini(#__VA_ARGS__);  \
for (char const* _c = ini; *_c; ++_c, ++_idx) if(*_c != ',' && *_c != ' ') chars[_idx] = *_c;  return chars;}(); \
static constexpr const char* _typeName = #Type; \
static constexpr std::array<const char*, tser::detail::n_args(#__VA_ARGS__)> _memberNames = \
[](){ std::array<const char*, tser::detail::n_args(#__VA_ARGS__)> out{ }; \
for(size_t _i = 0, nArgs = 0; nArgs < tser::detail::n_args(#__VA_ARGS__) ; ++_i) { \
while(Type::_memberNameData[_i] == '\0') _i++; out[nArgs++] = &Type::_memberNameData[_i]; \
while(Type::_memberNameData[++_i] != '\0'); } return out;}();\
template<typename OT, std::enable_if_t<std::is_same_v<OT,Type> && !tser::is_detected_v<tser::has_outstream_op_t, OT>, int> = 0>\
friend std::ostream& operator<<(std::ostream& os, const OT& t) { tser::print(os, t); return os; }