format_to.hpp

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// SPDX-License-Identifier: BSL-1.0
// SPDX-FileCopyrightText: Copyright (C) 2020 Tobias Hienzsch
 
#ifndef TETL_FORMAT_FORMAT_TO_HPP
#define TETL_FORMAT_FORMAT_TO_HPP
 
#include <etl/_format/argument.hpp>
#include <etl/_format/basic_format_context.hpp>
#include <etl/_type_traits/remove_cvref.hpp>
#include <etl/_vector/static_vector.hpp>
 
namespace etl {
template <typename Iter>
using diff_t = typename etl::iterator_traits<etl::remove_cvref_t<Iter>>::difference_type;
 
/// \brief Format args according to the format string fmt, and write the result
/// to the output iterator out.
///
/// https://en.cppreference.com/w/cpp/utility/format/format_to
template <typename OutputIt, typename... Args>
auto format_to(OutputIt out, etl::string_view fmt, Args const&... args) -> OutputIt
{
    auto ctx = format_context{out};
 
    // Format leading text before the first argument.
    auto const slices = detail::split_at_next_argument(fmt);
    detail::format_escaped_sequences(slices.first, ctx);
 
    // Save rest of format string. Supress warning if format_to was called
    // without arguments.
    auto rest = slices.second;
    etl::ignore_unused(rest);
 
    ([&] {
        // Format argument
        detail::format_argument(args, ctx);
 
        // Split format text at next argument
        auto const restSlices = detail::split_at_next_argument(rest);
        detail::format_escaped_sequences(restSlices.first, ctx);
 
        // Save rest of format string for the next arguments
        rest = restSlices.second;
    }(), ...);
 
    // Anything left over after the last argument.
    if (auto const trailing = detail::split_at_next_argument(rest); !trailing.first.empty()) {
        detail::format_escaped_sequences(trailing.first, ctx);
        TETL_ASSERT(trailing.second.empty());
    }
 
    return ctx.out();
}
 
/// \brief etl::format_to_n_result has no base classes, or members other than
/// out, size and implicitly declared special member functions.
///
/// https://en.cppreference.com/w/cpp/utility/format/format_to_n
template <typename Out>
struct format_to_n_result {
    Out out;
    diff_t<Out> size;
};
 
/// \brief Format args according to the format string fmt, and write the result
/// to the output iterator out. At most n characters are written.
///
/// https://en.cppreference.com/w/cpp/utility/format/format_to_n
template <typename OutputIter, typename... Args>
auto format_to_n(OutputIter out, diff_t<OutputIter> n, etl::string_view fmt, Args const&... args)
    -> format_to_n_result<OutputIter>
{
    etl::ignore_unused(n);
 
    auto indices = etl::static_vector<etl::size_t, sizeof...(args)>{};
    auto result  = format_to_n_result<OutputIter>{out, {}};
 
    auto writeChar = [&result](auto ch) {
        *result.out++ = ch;
        result.size++;
    };
 
    auto varStart = etl::size_t{};
    for (decltype(fmt)::size_type i{}; i < fmt.size(); ++i) {
        auto ch = fmt[i];
        if (ch == '{') {
            if ((fmt.size() > i + 1) && (fmt[i + 1] == '{')) {
                ++i;
                writeChar('{');
                continue;
            }
 
            varStart = i;
            continue;
        }
 
        if (ch == '}') {
            if ((fmt.size() > i + 1) && (fmt[i + 1] == '}')) {
                ++i;
                writeChar('}');
                continue;
            }
 
            indices.push_back(varStart);
            writeChar('0');
            continue;
        }
 
        writeChar(ch);
    }
 
    if (indices.size() > 0) {
        [[maybe_unused]] auto replaceCharAt = [n](auto output, auto pos, char val) {
            etl::ignore_unused(n);
            // TETL_ASSERT((long)pos < n);
            output[pos] = val;
        };
 
        [[maybe_unused]] typename decltype(indices)::size_type i{};
        (replaceCharAt(out, indices[i++], args), ...);
    }
 
    return result;
}
} // namespace etl
 
#endif // TETL_FORMAT_FORMAT_TO_HPP