endian_buffer.hpp

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/*
 * This file is part of OpenTTD.
 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <https://www.gnu.org/licenses/old-licenses/gpl-2.0>.
 */

 
#ifndef ENDIAN_BUFFER_HPP
#define ENDIAN_BUFFER_HPP
 
#include <string_view>
#include "../core/bitmath_func.hpp"
#include "../strings_type.h"

template <typename Tcont = typename std::vector<uint8_t>, typename Titer = typename std::back_insert_iterator<Tcont>>
class EndianBufferWriter {
  Titer buffer;
 
public:
  EndianBufferWriter(Titer buffer) : buffer(buffer) {}
  EndianBufferWriter(typename Titer::container_type &container) : buffer(std::back_inserter(container)) {}
 
  EndianBufferWriter &operator <<(const std::string &data) { return *this << std::string_view{ data }; }
  EndianBufferWriter &operator <<(const EncodedString &data) { return *this << data.string; }
  EndianBufferWriter &operator <<(std::string_view data) { this->Write(data); return *this; }
  EndianBufferWriter &operator <<(bool data) { return *this << static_cast<uint8_t>(data ? 1 : 0); }
 
  template <typename... Targs>
  EndianBufferWriter &operator <<(const std::tuple<Targs...> &data)
  {
    this->WriteTuple(data, std::index_sequence_for<Targs...>{});
    return *this;
  }
 
  template <typename... Targs>
  EndianBufferWriter &operator <<(const std::variant<Targs...> &variant)
  {
    this->WriteVariant(variant);
    return *this;
  }
 
  EndianBufferWriter &operator <<(const std::monostate &)
  {
    return *this;
  }
 
  EndianBufferWriter &operator <<(const ConvertibleThroughBase auto data)
  {
    this->Write(data.base());
    return *this;
  }
 
  template <class T> requires (!std::is_class_v<T>)
  EndianBufferWriter &operator <<(const T data)
  {
    if constexpr (std::is_enum_v<T>) {
      this->Write(to_underlying(data));
    } else {
      this->Write(data);
    }
    return *this;
  }
 
  template <typename Tvalue, typename Tbuf = std::vector<uint8_t>>
  static Tbuf FromValue(const Tvalue &data)
  {
    Tbuf buffer;
    EndianBufferWriter writer{ buffer };
    writer << data;
    return buffer;
  }
 
private:
  template <class Ttuple, size_t... Tindices>
  void WriteTuple(const Ttuple &values, std::index_sequence<Tindices...>)
  {
    ((*this << std::get<Tindices>(values)), ...);
  }
 
  template <typename T, std::size_t I = 0>
  void WriteVariant(const T &variant )
  {
    if constexpr (I < std::variant_size_v<T>) {
      if (I == variant.index()) {
        static_assert(std::variant_size_v<T> < std::numeric_limits<uint8_t>::max());
        this->Write(static_cast<uint8_t>(variant.index()));
        *this << std::get<I>(variant);
        return;
      }
 
      WriteVariant<T, I + 1>(variant);
    }
  }

  void Write(std::string_view value)
  {
    for (auto c : value) {
      this->buffer++ = c;
    }
    this->buffer++ = '\0';
  }

  template <class T>
  void Write(T value)
  {
    static_assert(sizeof(T) <= 8, "Value can't be larger than 8 bytes");
 
    if constexpr (sizeof(T) > 1) {
      this->buffer++ = GB(value, 0, 8);
      this->buffer++ = GB(value, 8, 8);
      if constexpr (sizeof(T) > 2) {
        this->buffer++ = GB(value, 16, 8);
        this->buffer++ = GB(value, 24, 8);
      }
      if constexpr (sizeof(T) > 4) {
        this->buffer++ = GB(value, 32, 8);
        this->buffer++ = GB(value, 40, 8);
        this->buffer++ = GB(value, 48, 8);
        this->buffer++ = GB(value, 56, 8);
      }
    } else {
      this->buffer++ = value;
    }
  }
};

class EndianBufferReader {
  std::span<const uint8_t> buffer;
  size_t read_pos = 0;
 
public:
  EndianBufferReader(std::span<const uint8_t> buffer) : buffer(buffer) {}
 
  void rewind() { this->read_pos = 0; }
 
  EndianBufferReader &operator >>(std::string &data) { data = this->ReadStr(); return *this; }
  EndianBufferReader &operator >>(EncodedString &data) { data = EncodedString{this->ReadStr()}; return *this; }
  EndianBufferReader &operator >>(bool &data) { data = this->Read<uint8_t>() != 0; return *this; }
 
  template <typename... Targs>
  EndianBufferReader &operator >>(std::tuple<Targs...> &data)
  {
    this->ReadTuple(data, std::index_sequence_for<Targs...>{});
    return *this;
  }
 
  template <typename... Targs>
  EndianBufferReader &operator >>(std::variant<Targs...> &variant)
  {
    this->ReadVariant(this->Read<uint8_t>(), variant);
    return *this;
  }
 
  EndianBufferReader &operator >>(const std::monostate &)
  {
    return *this;
  }
 
  template <ConvertibleThroughBase T>
  EndianBufferReader &operator >>(T &data)
  {
    data = T{this->Read<typename T::BaseType>()};
    return *this;
  }
 
  template <class T> requires (!std::is_class_v<T>)
  EndianBufferReader &operator >>(T &data)
  {
    if constexpr (std::is_enum_v<T>) {
      data = static_cast<T>(this->Read<std::underlying_type_t<T>>());
    } else {
      data = this->Read<T>();
    }
    return *this;
  }
 
  template <typename Tvalue>
  static Tvalue ToValue(std::span<const uint8_t> buffer)
  {
    Tvalue result{};
    EndianBufferReader reader{ buffer };
    reader >> result;
    return result;
  }
 
private:
  template <class Ttuple, size_t... Tindices>
  void ReadTuple(Ttuple &values, std::index_sequence<Tindices...>)
  {
    ((*this >> std::get<Tindices>(values)), ...);
  }
 
  template <typename T, std::size_t I = 0>
  void ReadVariant(uint8_t index, T &variant)
  {
    if constexpr (I < std::variant_size_v<T>) {
      if (I != index) {
        ReadVariant<T, I + 1>(index, variant);
        return;
      }
 
      std::variant_alternative_t<I, T> data;
      *this >> data;
      variant = data;
    }
  }

  std::string ReadStr()
  {
    std::string str;
    while (this->read_pos < this->buffer.size()) {
      char ch = this->Read<char>();
      if (ch == '\0') break;
      str.push_back(ch);
    }
    return str;
  }

  template <class T>
  T Read()
  {
    static_assert(!std::is_const_v<T>, "Can't read into const variables");
    static_assert(sizeof(T) <= 8, "Value can't be larger than 8 bytes");
 
    if (read_pos + sizeof(T) > this->buffer.size()) return {};
 
    T value = static_cast<T>(this->buffer[this->read_pos++]);
    if constexpr (sizeof(T) > 1) {
      value += static_cast<T>(this->buffer[this->read_pos++]) << 8;
    }
    if constexpr (sizeof(T) > 2) {
      value += static_cast<T>(this->buffer[this->read_pos++]) << 16;
      value += static_cast<T>(this->buffer[this->read_pos++]) << 24;
    }
    if constexpr (sizeof(T) > 4) {
      value += static_cast<T>(this->buffer[this->read_pos++]) << 32;
      value += static_cast<T>(this->buffer[this->read_pos++]) << 40;
      value += static_cast<T>(this->buffer[this->read_pos++]) << 48;
      value += static_cast<T>(this->buffer[this->read_pos++]) << 56;
    }
 
    return value;
  }
};
 
#endif /* ENDIAN_BUFFER_HPP */