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

module;

#include <expected>
#include <iosfwd>
#include <string>

export module nihil.config:option;

import nihil.error;
import nihil.ucl;

namespace nihil::config {

/*
 * Base class for options; this is what config_store interacts with.
 *
 * Base classes should override the four protected functions:
 *
 * 	get_string()
 * 	set_string()
 * 	get_ucl()
 * 	set_ucl()
 *
 * Overriding any other members is not permitted.
 */

export struct option
{
	virtual ~option();

	// Short name of this option.
	[[nodiscard]] auto name(this option const &) noexcept
		-> std::string_view;

	// Human-readable description of this option.
	[[nodiscard]] auto description(this option const &) noexcept
		-> std::string_view;

	// If true, this option is set to its default value.
	[[nodiscard]] auto is_default(this option const &) noexcept
		-> bool;

	/*
	 * Get or set this option as a string.  The specific conversion
	 * method depends on the derived option type.
	 */
	[[nodiscard]] auto string(this option const &) -> std::string;
	[[nodiscard]] auto string(this option &, std::string_view value)
		-> std::expected<void, error>;

	/*
	 * Return this object as a UCL object.  This is used when writing the
	 * configuration file.
	 */
	[[nodiscard]] auto ucl(this option const &)
		-> std::expected<ucl::object, error>;

	/*
	 * Set this object from a UCL object.  This is used when reading the
	 * configuration file.
	 */
	[[nodiscard]] auto ucl(this option &, ucl::object const &)
		-> std::expected<void, error>;

	// Not copyable or movable.
	option(option const &) = delete;
	auto operator=(option const &) -> option& = delete;

protected:
	option(std::string_view name, std::string_view description);

	auto is_default(this option &, bool) -> void;

	/*
	 * Get or set this option as a string.
	 */
	[[nodiscard]] virtual auto get_string() const
		-> std::string = 0;
	[[nodiscard]] virtual auto set_string(std::string_view)
		-> std::expected<void, error> = 0;

	/*
	 * Get or set this option as a UCL object.
	 */
	[[nodiscard]] virtual auto get_ucl() const
		-> std::expected<ucl::object, error> = 0;
	[[nodiscard]] virtual auto set_ucl(ucl::object const &)
		-> std::expected<void, error> = 0;

private:
	std::string	m_name;
	std::string	m_description;
	bool		m_is_default = true;
};

/*
 * Make options printable.  This is mostly useful for testing.
 */
export auto operator<<(std::ostream &strm, option const &opt) -> std::ostream &;

} // namespace nihil