daw_json_option_bits.h

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// Copyright (c) Darrell Wright
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE or copy at http://www.boost.org/LICENSE_1_0.txt)
//
// Official repository: https://github.com/beached/daw_json_link
//
 
#pragma once
 
#include "version.h"
 
#include <daw/cpp_17.h>
#include <daw/daw_attributes.h>
#include <daw/daw_traits.h>
 
#include <climits>
#include <cstddef>
#include <cstdint>
#include <utility>
 
namespace daw::json {
  inline namespace DAW_JSON_VER {
    using json_options_t = std::uint32_t;
    namespace json_details {
 
      template<typename>
      inline constexpr unsigned json_option_bits_width = 0;
 
      template<typename>
      inline constexpr auto default_json_option_value = [] {
        struct unknown_policy {};
        return unknown_policy{ };
      }( );
 
      template<typename Policy, typename Options>
      struct option_bits_start_impl;
 
      template<typename Policy, typename... Options>
      struct option_bits_start_impl<Policy, pack_list<Options...>> {
        static constexpr auto idx =
          daw::traits::pack_index_of_v<Policy, Options...>;
        static_assert( idx >= 0, "Policy is not registered" );
        using tp_policies = pack_list<Options...>;
 
        template<std::size_t Pos, int End>
        static constexpr unsigned do_step( ) {
          if constexpr( Pos >= static_cast<std::size_t>( End ) ) {
            return 0U;
          }
          return json_option_bits_width<pack_element_t<Pos, tp_policies>>;
        }
 
        template<std::size_t... Is>
        DAW_ATTRIB_INLINE static constexpr unsigned
        calc( std::index_sequence<Is...> ) {
          return ( do_step<Is, idx>( ) + ... );
        }
      };
 
      template<typename... Options>
      struct option_list_impl {
        using type = pack_list<Options...>;
 
        static_assert(
          ( json_option_bits_width<Options> + ... + 0 ) <=
            ( sizeof( json_options_t ) * CHAR_BIT ),
          "The size of json_options_t is not large enough "
          "to safely hold all the bits of state.  Use a larger size." );
      };
 
      template<typename Option>
      inline constexpr bool is_option_flag = json_option_bits_width<Option> > 0;
 
      template<typename... Options>
      inline constexpr bool are_option_flags =
        ( is_option_flag<Options> and ... );
 
      template<typename Option, typename Options>
      inline constexpr unsigned basic_option_bits_start =
        option_bits_start_impl<Option, Options>::template calc<>(
          std::make_index_sequence<pack_size_v<Options>>{ } );
 
      template<typename... JsonOptions>
      struct JsonOptionList;
 
      template<typename... OptionList, typename Option>
      static constexpr json_options_t
      set_bits_for( JsonOptionList<OptionList...>, Option e );
 
      template<typename... JsonOptions>
      struct JsonOptionList {
        using OptionList = typename option_list_impl<JsonOptions...>::type;
 
        template<typename Option>
        static inline constexpr unsigned option_bits_start =
          basic_option_bits_start<Option, OptionList>;
 
        template<typename... /*OptionList*/, typename Option>
        static constexpr json_options_t set_bits_for( Option e ) {
          static_assert( is_option_flag<Option>,
                         "Only registered policy types are allowed" );
          auto new_bits = static_cast<json_options_t>( e );
          new_bits <<= option_bits_start<Option>;
          return new_bits;
        }
 
        static constexpr json_options_t default_option_flag =
          ( set_bits_for<JsonOptions>(
              default_json_option_value<JsonOptions> ) |
            ... | 0 );
        /***
         * Create the parser options flag for BasicParseOption
         * @tparam Options Option types that satisfy the `is_option_flag`
         * trait.
         * @param policies A list of parser options to change from the defaults.
         * @return A json_options_t that encodes the options for the parser
         */
        template<typename... Options>
        static constexpr json_options_t options( Options... options ) {
          static_assert( json_details::are_option_flags<Options...>,
                         "Only registered option types are allowed" );
          auto result = default_option_flag;
          if constexpr( sizeof...( Options ) > 0 ) {
            result |= ( set_bits_for( options ) | ... );
          }
          return result;
        }
      };
 
      template<typename... OptionList, typename Option>
      constexpr void set_bits_in( JsonOptionList<OptionList...>,
                                  json_options_t &value, Option e ) {
        static_assert( is_option_flag<Option>,
                       "Only registered policy types are allowed" );
        auto new_bits = static_cast<unsigned>( e );
        constexpr unsigned mask = (1U << json_option_bits_width<Option>)-1U;
        new_bits &= mask;
        new_bits <<=
          JsonOptionList<OptionList...>::template option_bits_start<Option>;
        value &= ~mask;
        value |= new_bits;
      }
 
      template<typename... OptionList, typename Option, typename... Options>
      constexpr json_options_t set_bits( JsonOptionList<OptionList...>,
                                         json_options_t value, Option pol,
                                         Options... pols ) {
        static_assert( are_option_flags<Options...>,
                       "Only registered policy types are allowed" );
 
        auto new_bits = static_cast<unsigned>( pol );
        constexpr unsigned mask = ( (1U << json_option_bits_width<Option>)-1U );
        new_bits &= mask;
        new_bits <<=
          JsonOptionList<OptionList...>::template option_bits_start<Option>;
        value &= ~( mask << JsonOptionList<
                      OptionList...>::template option_bits_start<Option> );
        value |= new_bits;
        if constexpr( sizeof...( Options ) > 0 ) {
          return set_bits( JsonOptionList<OptionList...>{ }, value, pols... );
        } else {
          return value;
        }
      }
 
      template<typename... OptionList, typename Option>
      static constexpr json_options_t
      set_bits_for( JsonOptionList<OptionList...>, Option e ) {
        return JsonOptionList<OptionList...>::set_bits_for( e );
      }
 
      template<typename Option, typename Result = Option,
               typename... OptionList>
      constexpr Result get_bits_for( JsonOptionList<OptionList...>,
                                     json_options_t value ) {
        static_assert( std::is_enum_v<Option>,
                       "Only enum options are allowed" );
        static_assert( std::is_same_v<unsigned, std::underlying_type_t<Option>>,
                       "Looks like option was no specified correctly.  "
                       "Underlying type should be unsigned" );
        static_assert( is_option_flag<Option>,
                       "Only registered option types are allowed" );
        constexpr unsigned mask =
          ( 1U << (JsonOptionList<OptionList...>::template option_bits_start<
                     Option> +
                   json_option_bits_width<Option>)) -
          1U;
        value &= mask;
        value >>=
          JsonOptionList<OptionList...>::template option_bits_start<Option>;
        return static_cast<Result>( Option{ value } );
      }
 
      template<typename... OptionList, typename... Options>
      constexpr json_options_t json_option( JsonOptionList<OptionList...>,
                                            Options... options ) {
        return JsonOptionList<OptionList...>::options( options... );
      }
 
      template<typename>
      struct default_option_flag_t;
 
      template<template<class...> class OptionList, typename... Options>
      struct default_option_flag_t<OptionList<Options...>> {
        static constexpr json_options_t value =
          ( OptionList<Options...>::template set_bits_for<Options>(
              default_json_option_value<Options> ) |
            ... );
      };
 
      /***
       * The defaults for all known policies encoded as a json_options_t
       */
      template<typename OptionList>
      static inline constexpr json_options_t default_option_flag =
        default_option_flag_t<OptionList>::value;
 
    } // namespace json_details
  } // namespace DAW_JSON_VER
} // namespace daw::json