// This source code is released into the public domain.
module;

#include <cerrno>
#include <stdlib.h> // NOLINT: getenv_r

#include "nihil.hh"

export module nihil.posix:getenv;

import nihil.std;
import nihil.util;

namespace nihil {


// Find a variable by the given name in the environment by calling getenv_r() if available,
// or getenv() if not.  In either case the value is copied, so will not be affected by
// future calls to setenv().
export [[nodiscard]] auto getenv(std::string_view varname) -> std::expected<std::string, error>
{
	auto errno_guard = save_errno();
	auto cvarname = std::string(varname);

#if NIHIL_HAVE_GETENV_R == 1
	// Start with a buffer of this size, and double it every iteration.
	constexpr auto bufinc = std::size_t{1024};

	auto buf = std::vector<char>(bufinc);
	for (;;) {
		auto const ret = ::getenv_r(cvarname.c_str(), buf.data(), buf.size());

		if (ret == 0)
			return {std::string(buf.data())};

		if (ret == -1 && errno == ERANGE) {
			buf.resize(buf.size() * 2);
			continue;
		}

		return std::unexpected(error(std::errc(errno)));
	}
#else  // NIHIL_HAVE_GETENV_R
	// getenv() may not set errno on failure, so initialise it to a reasonable value.
	errno = ENOENT;
	auto const *v = ::getenv(cvarname.c_str()); // NOLINT

	if (v != nullptr)
		return {std::string(v)};

	return error(sys_error());
#endif // NIHIL_HAVE_GETENV_R
}

} // namespace nihil