vpresent_encoded_context.h

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#pragma once
 
#include "di/assert/assert_bool.h"
#include "di/container/string/string_view_impl.h"
#include "di/format/concepts/format_arg.h"
#include "di/format/concepts/format_args.h"
#include "di/format/format_arg.h"
#include "di/format/format_args.h"
#include "di/format/format_parse_context.h"
#include "di/format/formatter.h"
#include "di/function/monad/monad_try.h"
#include "di/vocab/optional/prelude.h"
 
namespace di::format {
namespace detail {
    template<concepts::Encoding Enc, typename Var>
    constexpr auto do_format(Var&& variant, FormatParseContext<Enc>& parse_context,
                             concepts::FormatContext auto& context, bool debug = false) -> Result<void> {
        return di::visit<Result<void>>(
            [&]<typename T>(T&& value) -> Result<void> {
                if constexpr (concepts::InstanceOf<meta::RemoveCVRef<T>, ErasedArg>) {
                    return value.do_format(parse_context, context, debug);
                } else {
                    auto formatter = DI_TRY(format::formatter<meta::RemoveCVRef<T>, Enc>(parse_context, debug));
                    return formatter(context, value);
                }
            },
            variant);
    }
 
    template<concepts::Encoding Enc>
    struct VPresentEncodedContextFunction {
        using View = container::string::StringViewImpl<Enc>;
 
        template<concepts::FormatArg Arg>
        constexpr auto operator()(View format, FormatArgs<Arg> args, concepts::FormatContext auto& context,
                                  bool debug = false) const -> Result<void> {
            auto parse_context = FormatParseContext<Enc> { format, args.size() };
 
            for (auto value : parse_context) {
                DI_ASSERT(value);
 
                // Literal text.
                if (value->index() == 0) {
                    for (auto code_point : util::get<0>(*value)) {
                        context.output(code_point);
                    }
                    continue;
                }
 
                // Format argument.
                auto arg_index = util::get<1>(*value).index;
                DI_TRY(do_format(args[arg_index], parse_context, context, debug));
            }
            return {};
        }
    };
}
 
template<concepts::Encoding Enc>
constexpr inline auto vpresent_encoded_context = detail::VPresentEncodedContextFunction<Enc> {};
}