// This source code is released into the public domain.
export module nihil.core:capture_stream;

import nihil.std;

namespace nihil {

// Capture output written to a stream and redirect it to an internal string
// buffer.  Call .str() to get the data written.  Call .release() to stop
// capturing (or simply delete the capture_stream object).
export template<typename Char, typename Traits>
struct capture_stream {
	capture_stream(std::basic_ostream<Char, Traits> &stream)
		: m_stream(&stream)
	{
		m_old_streambuf = m_stream->rdbuf();
		m_stream->rdbuf(m_buffer.rdbuf());
	}

	~capture_stream()
	{
		if (m_old_streambuf == nullptr)
			return;
		m_stream->rdbuf(m_old_streambuf);
	}

	/*
	 * Release this capture, returning the stream to its previous state.
	 */
	auto release(this capture_stream &self) -> void
	{
		if (self.m_old_streambuf == nullptr)
			throw std::logic_error(
				"release() called on empty capture_stream");

		self.m_stream->rdbuf(self.m_old_streambuf);
		self.m_old_streambuf = nullptr;
	}

	/*
	 * Get the data which has been written to the stream.
	 */
	[[nodiscard]] auto str(this capture_stream const &self)
		-> std::basic_string_view<Char, Traits>
	{
		return self.m_buffer.view();
	}

private:
	std::basic_ostringstream<Char, Traits>	 m_buffer;
	std::basic_ostream<Char, Traits>	*m_stream;
	std::streambuf				*m_old_streambuf;
};

} // namespace nihil