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

module;

/*
 * Exec providers, mostly used for spawn().
 */

#include <expected>
#include <string>

export module nihil.posix:exec;

import nihil.error;
import :argv;
import :fd;

namespace nihil {

/*
 * A concept to mark spawn executors.
 */

export struct exec_tag{};

export template<typename T>
concept executor =
	requires (T e) {
		std::same_as<exec_tag, typename std::remove_cvref_t<T>::tag>;
		{ e.exec() };
	};

/*
 * fexecv: use a file descriptor and an argument vector to call ::fexecve().
 * This is the lowest-level executor which all others are implemented
 * in terms of.
 *
 * TODO: Should have a way to pass the environment (envp).
 */
export struct fexecv final {
	using tag = exec_tag;

	fexecv(fd &&execfd, argv &&args) noexcept;

	[[nodiscard]] auto exec(this fexecv &self) 
		-> std::expected<void, error>;

	// Movable
	fexecv(fexecv &&) noexcept;
	auto operator=(this fexecv &, fexecv &&) noexcept -> fexecv&;
	
	// Not copyable (because we hold the open fd object)
	fexecv(fexecv const &) = delete;
	auto operator=(this fexecv &, fexecv const &) -> fexecv& = delete;

private:
	fd	m_execfd;
	argv	m_args;
};

/*
 * execv: equivalent to fexecv(), except the command is passed as
 * a pathname instead of a file descriptor.  Does not search $PATH.
 */
export [[nodiscard]] auto execv(std::string_view path, argv &&argv)
	-> std::expected<fexecv, error>;

/*
 * execvp: equivalent to fexecv(), except the command is passed as
 * a filename instead of a file descriptor.  If the filename is not
 * an absolute path, it will be searched for in $PATH.
 */
export [[nodiscard]] auto execvp(std::string_view file, argv &&argv)
	-> std::expected<fexecv, error>;

/*
 * execl: equivalent to execv, except the arguments are passed as a
 * variadic pack of string-like objects.
 */
export [[nodiscard]] auto execl(std::string_view path, auto &&...args)
	-> std::expected<fexecv, error>
{
	return execv(path, argv({std::string_view(args)...}));
}

/*
 * execlp: equivalent to execvp, except the arguments are passed as a
 * variadic pack of string-like objects.
 */
export [[nodiscard]] auto execlp(std::string_view file, auto &&...args)
	-> std::expected<fexecv, error>
{
	return execvp(file, argv({std::string_view(args)...}));
}

/*
 * shell: run the process by invoking /bin/sh -c with the single argument,
 * equivalent to system(3).
 */
export [[nodiscard]] auto shell(std::string_view const &command)
	-> std::expected<fexecv, error>;

} // namespace nihil