#include "kapi/cio.hpp"

#include <kstd/format>
#include <kstd/os/print.hpp>
#include <kstd/print>

#include <array>
#include <cstddef>
#include <iterator>
#include <string_view>

namespace kstd::os
{

  namespace
  {
    struct write_buffer
    {
      using output_stream = kapi::cio::output_stream;

      constexpr auto static size = 128uz;

      write_buffer(write_buffer const &) = delete;
      write_buffer(write_buffer &&) = delete;
      auto operator=(write_buffer const &) -> write_buffer & = delete;
      auto operator=(write_buffer &&) -> write_buffer & = delete;

      explicit write_buffer(output_stream stream)
          : m_stream{stream}
      {}

      ~write_buffer() noexcept
      {
        flush();
      }

      auto flush() noexcept -> void
      {
        if (m_position > 0)
        {
          std::string_view chunk{m_buffer.data(), m_position};
          kapi::cio::write(m_stream, chunk);
          m_position = 0;
        }
      }

      auto static callback(void * object, std::string_view text) -> void
      {
        auto * self = static_cast<write_buffer *>(object);
        for (char const character : text)
        {
          if (self->m_position >= size)
          {
            self->flush();
          }
          self->m_buffer.at(self->m_position++) = character;
        }
      }

    private:
      output_stream m_stream;
      std::array<char, size> m_buffer{};
      std::size_t m_position{};
    };

  }  // namespace

  auto vprint(print_sink sink, std::string_view format, kstd::format_args args) -> void
  {
    auto writer = write_buffer{(sink == print_sink::stderr) ? kapi::cio::output_stream::stderr
                                                            : kapi::cio::output_stream::stdout};
    auto context = kstd::format_context{.writer = write_buffer::callback, .user_data = &writer};

    auto current = format.begin();
    auto end = format.end();
    auto next_automatic_index = 0uz;

    while (current != end)
    {
      if (*current != '{')
      {
        auto start = current;
        while (current != end && *current != '{')
        {
          std::advance(current, 1);
        }
        context.push(std::string_view(start, current - start));
        continue;
      }

      if (std::next(current) != end && *(std::next(current)) == '{')
      {
        context.push('{');
        std::advance(current, 2);
        continue;
      }

      std::advance(current, 1);

      auto index = 0uz;
      if (current != end && *current >= '0' && *current <= '9')
      {
        while (current != end && *current >= '0' && *current <= '9')
        {
          index = index * 10 + static_cast<std::size_t>(*current - '0');
          std::advance(current, 1);
        }
      }
      else
      {
        index = next_automatic_index++;
      }

      auto remaining_fmt = std::string_view{current, static_cast<std::size_t>(std::distance(current, end))};

      auto const arg = args.get(index);
      if (arg.format)
      {
        auto const after_specs = arg.format(arg.value, remaining_fmt, context);
        auto const consumed = remaining_fmt.size() - after_specs.size();
        std::advance(current, consumed);
      }
      else
      {
        context.push("{?}");
        while (current != end && *current != '}')
          std::advance(current, 1);
      }

      if (current != end && *current == '}')
      {
        std::advance(current, 1);
      }
      else
      {
        context.push("{fmt-err}");
        while (current != end && *current != '}')
          std::advance(current, 1);
        if (current != end)
          std::advance(current, 1);
      }
    }
  }

}  // namespace kstd::os