parser_variant.hpp

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/*
   This file is part of PLYwoot, a header-only PLY parser.
 
   Copyright (C) 2023-2025, Ton van den Heuvel
 
   PLYwoot 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, either version 3 of the License, or
   (at your option) any later version.
 
   This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
*/
 
#ifndef PLYWOOT_PARSER_VARIANT_HPP
#define PLYWOOT_PARSER_VARIANT_HPP
 
 
#include "ascii_parser_policy.hpp"
#include "binary_parser_policy.hpp"
#include "parser.hpp"
 
#include <istream>
#include <variant>
 
namespace plywoot::detail {
 
class ParserVariant
{
public:
  ParserVariant(std::istream &is, PlyFormat format) : variant_{makeVariant(is, format)} {}
 
  PlyElementData read(const PlyElement &element) const
  {
    return std::visit([&](auto &&parser) { return parser.read(element); }, variant_);
  }
 
  template<typename Layout>
  void read(const PlyElement &element, std::uint8_t *dest, std::size_t alignment) const
  {
    VisitHelper<Layout>::visit(element, dest, alignment, variant_);
  }
 
  void skip(const PlyElement &element) const
  {
    std::visit([&element](auto &&parser) { parser.skip(element); }, variant_);
  }
 
private:
  using Variant = std::variant<
      detail::Parser<detail::AsciiParserPolicy>,
      detail::Parser<detail::BinaryBigEndianParserPolicy>,
      detail::Parser<detail::BinaryLittleEndianParserPolicy>>;
 
  // Note; VisitHelper exists to be able to extract `Ts...` from `Layout`.
  template<typename Layout>
  struct VisitHelper;
 
  template<template <typename ...> class Layout, typename ...Ts>
  struct VisitHelper<Layout<Ts...>>
  {
    static void visit(const PlyElement &element, std::uint8_t *dest, std::size_t alignment, const Variant &v)
    {
      std::visit([&element, dest, alignment](auto &&parser) { parser.template read<Ts...>(element, dest, alignment); }, v);
    }
  };
 
  Variant makeVariant(std::istream &is, PlyFormat format)
  {
    switch (format)
    {
      case PlyFormat::Ascii:
        return Variant{std::in_place_type<detail::Parser<detail::AsciiParserPolicy>>, is};
      case PlyFormat::BinaryBigEndian:
        return Variant{std::in_place_type<detail::Parser<detail::BinaryBigEndianParserPolicy>>, is};
      case PlyFormat::BinaryLittleEndian:
      default:
        break;
    }
 
    return Variant{std::in_place_type<detail::Parser<detail::BinaryLittleEndianParserPolicy>>, is};
  }
 
  Variant variant_;
};
 
}
 
#endif