module;

#include <asio.hpp>

#include <csignal>
#include <format>
#include <system_error>

export module ttwhy.terminal:signal_handling;

namespace ttwhy::terminal
{

  //! Asynchronously handle POSIX process and job-control signals for a terminal application.
  //!
  //! Intercepts SIGINT and SIGTERM to print an exit notification and terminate gracefully.
  //! Intercepts SIGTSTP to restore terminal canonical and echo flags before raising SIGSTOP,
  //! and intercepts SIGCONT to restore the terminal attributes when execution resumes.
  //!
  //! @tparam Stream The output stream type used for writing diagnostic messages.
  //! @tparam TerminalAttributes The terminal attributes manager type.
  //! @param stream The stream to write diagnostic messages to.
  //! @param attributes The scoped attributes managing terminal canonical mode and echo.
  //! @return An awaitable task that yields an error code upon termination.
  export template<typename Stream, typename TerminalAttributes>
  auto handle_signals(Stream & stream, TerminalAttributes & attributes) -> asio::awaitable<std::error_code>
  {
    auto executor = co_await asio::this_coro::executor;
    auto signals = asio::signal_set{executor, SIGINT, SIGTERM};
    signals.add(SIGTSTP);
    signals.add(SIGCONT);

    while (true)
    {
      auto [error, signal] = co_await signals.async_wait(asio::as_tuple(asio::use_awaitable));
      if (error)
      {
        co_return error;
      }

      switch (signal)
      {
        case SIGINT:
        case SIGTERM:
        {
          auto message = std::format("Received signal {}, exiting ...\n", signal);
          co_await asio::async_write(stream, asio::buffer(message), asio::use_awaitable);
          co_return asio::error_code{};
        }
        case SIGTSTP:
        {
          attributes.canonical_mode(true).echo(true);
          ::raise(SIGSTOP);
          break;
        }
        case SIGCONT:
        {
          attributes.canonical_mode(false).echo(false);
          break;
        }
      }
    }
  }

}  // namespace ttwhy::terminal