module;

#include <termios.h>
#include <unistd.h>

#include <cerrno>
#include <system_error>
#include <utility>

export module ttwhy:scoped_attributes;

namespace ttwhy
{

  auto static read_attributes(int file_descriptor) -> termios
  {
    auto active_attributes = termios{};
    if (::tcgetattr(file_descriptor, &active_attributes))
    {
      throw std::system_error(errno, std::system_category(), "failed to read termios attributes");
    }
    return active_attributes;
  }

  auto static get_line_discipline_flag(int file_descriptor, int flag) -> bool
  {
    auto active_attributes = read_attributes(file_descriptor);
    return active_attributes.c_lflag & flag;
  }

  auto static set_line_discipline_flag(int file_descriptor, int flag, bool enabled) -> void
  {
    auto active_attributes = read_attributes(file_descriptor);

    if ((active_attributes.c_lflag & flag) == enabled)
    {
      return;
    }

    if (enabled)
    {
      active_attributes.c_lflag = active_attributes.c_lflag | flag;
    }
    else
    {
      active_attributes.c_lflag = active_attributes.c_lflag & ~flag;
    }

    if (::tcsetattr(file_descriptor, TCSANOW, &active_attributes))
    {
      throw std::system_error(errno, std::system_category(), "failed to write termios attributes");
    }
  }

  //! Store the current TC attributes and restore them on destruction.
  export struct scoped_attributes
  {
    explicit scoped_attributes(int file_descriptor)
        : m_file_descriptor{::dup(file_descriptor)}
        , m_attributes{read_attributes(file_descriptor)}
    {}

    scoped_attributes(scoped_attributes const &) = delete;

    scoped_attributes(scoped_attributes && other)
        : m_file_descriptor{std::exchange(other.m_file_descriptor, -1)}
        , m_attributes{std::move(other.m_attributes)}
    {}

    ~scoped_attributes()
    {
      if (m_file_descriptor > 0)
      {
        ::tcsetattr(m_file_descriptor, TCSANOW, &m_attributes);
        ::close(m_file_descriptor);
      }
    }

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

    auto operator=(scoped_attributes && other) -> scoped_attributes &
    {
      std::ranges::swap(m_file_descriptor, other.m_file_descriptor);
      std::ranges::swap(m_attributes, other.m_attributes);
      return *this;
    }

    //! Check if canonical mode is currently active
    [[nodiscard]] auto canonical_mode() const noexcept -> bool
    {
      return get_line_discipline_flag(m_file_descriptor, ICANON);
    }

    //! Set whether canonical mode is active or not.
    auto canonical_mode(bool enabled) & -> scoped_attributes &
    {
      set_line_discipline_flag(m_file_descriptor, ICANON, enabled);
      return *this;
    }

    auto canonical_mode(bool enabled) && -> scoped_attributes
    {
      set_line_discipline_flag(m_file_descriptor, ICANON, enabled);
      return std::move(*this);
    }

    [[nodiscard]] auto echo() const noexcept -> bool
    {
      return get_line_discipline_flag(m_file_descriptor, ECHO);
    }

    auto echo(bool enabled) & -> scoped_attributes &
    {
      set_line_discipline_flag(m_file_descriptor, ECHO, enabled);
      return *this;
    }

    auto echo(bool enabled) && -> scoped_attributes
    {
      set_line_discipline_flag(m_file_descriptor, ECHO, enabled);
      return std::move(*this);
    }

  private:
    int m_file_descriptor;
    termios m_attributes;
  };

}  // namespace ttwhy