/*
 * This source code is released into the public domain.
 */

module;

#include <coroutine>
#include <expected>
#include <filesystem>
#include <ranges>
#include <system_error>
#include <vector>

#include <fcntl.h>
#include <unistd.h>

export module nihil:write_file;

import :error;
import :guard;
import :monad;
import :open_file;
import :rename_file;

namespace nihil {

/*
 * Write the contents of a range to a file.  Returns the number of bytes
 * written.
 */
export [[nodiscard]]
auto write_file(std::filesystem::path const &filename,
		std::ranges::contiguous_range auto &&range,
		int mode = 0777)
	-> std::expected<std::size_t, error>
{
	auto file = co_await open_file(filename, O_CREAT|O_WRONLY, mode);
	auto nbytes = co_await write(file, range);
	co_return nbytes;
}

/*
 * Utility wrapper for non-contiguous ranges.
 */
export [[nodiscard]]
auto write_file(std::filesystem::path const &filename,
		std::ranges::range auto &&range)
	-> std::expected<std::size_t, error>
requires(!std::ranges::contiguous_range<decltype(range)>)
{
	return write_file(filename, std::vector(std::from_range, range));
}

/*
 * Write the contents of a range to a file safely.  The data will be written
 * to "<filename>.tmp", and if the write succeeds, the temporary file will be
 * renamed to the target filename.  If an error occurs, the target file will
 * not be modified.
 */
export [[nodiscard]]
auto safe_write_file(std::filesystem::path const &filename,
		     std::ranges::range auto &&range)
	-> std::expected<void, error>
{
	auto tmpfile = filename;
	tmpfile.remove_filename();
	tmpfile /= (filename.filename().native() + ".tmp");

	auto tmpfile_guard = guard([&tmpfile] {
		::unlink(tmpfile.c_str());
	});

	co_await write_file(tmpfile, range);
	co_await rename_file(tmpfile, filename);

	tmpfile_guard.release();
	co_return {};
}


} // namespace nihil