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

#include <unistd.h> // access()

export module nihil.posix:find_in_path;

import nihil.std;
import nihil.core;
import :fd;
import :getenv;
import :paths;

namespace nihil {

// Find an executable by searching the given path string, which should be a colon-separated list of
// directories, and return the full path.  If the file can't be found or is not executable, returns
// an appropriate error.
export [[nodiscard]] auto find_in_path(std::filesystem::path const &file, std::string_view path)
	-> std::expected<std::filesystem::path, error>
{
	auto try_return =
		[](std::filesystem::path file) -> std::expected<std::filesystem::path, error> {
		auto ret = ::access(file.string().c_str(), X_OK);
		if (ret == 0)
			return {std::move(file)};
		return std::unexpected(error(sys_error()));
	};

	// Absolute pathname skips the search.
	if (file.is_absolute())
		return try_return(file);

	// Default to ENOENT as the error.
	auto err = error(std::errc::no_such_file_or_directory);

	for (auto &&dir : path | std::views::split(':')) {
		// An empty $PATH element means cwd.
		auto sdir = dir.empty() ? std::filesystem::path(".")
		                        : std::filesystem::path(std::string_view(dir));

		if (auto ret = try_return(sdir / file); ret)
			return ret;
		// If we get an error other than ENOENT, cache it to return to the caller.
		// This means we can propagate access() errors.
		else if (ret.error().root_cause() != std::errc::no_such_file_or_directory)
			err = std::move(ret.error());
	}

	return std::unexpected(std::move(err));
}

// Find an executable in $PATH and return the full path.  If $PATH is not set, uses _PATH_DEFPATH.
// If the file can't be found or is not executable, returns an appropriate error.
export [[nodiscard]] auto
find_in_path(std::filesystem::path const &file) -> std::expected<std::filesystem::path, error>
{
	auto const path = getenv("PATH").value_or(std::string(paths::defpath)); // NOLINT
	return find_in_path(file, path);
}

} // namespace nihil