// =====================================================================================================================
//  fennec, a free and open source game engine
//  Copyright © 2025 - 2026  Medusa Slockbower
//
//  This program is free software: you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
//
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with this program.  If not, see <https://www.gnu.org/licenses/>.
// =====================================================================================================================

///
/// \file fennec/lang/function.h
/// \brief
///
///
/// \details
/// \author Medusa Slockbower
///
/// \copyright Copyright © 2025 - 2026 Medusa Slockbower ([GPLv3](https://www.gnu.org/licenses/gpl-3.0.en.html))
///
///


#ifndef FENNEC_LANG_FUNCTION_H
#define FENNEC_LANG_FUNCTION_H

#include <fennec/lang/types.h>
#include <fennec/lang/assert.h>
#include <fennec/lang/utility.h>

#include <fennec/lang/detail/_function.h>

namespace fennec
{
///
/// \brief a class capable of holding a function or non-capturing lambda
template<typename> class function;

///
/// \brief a class capable of holding a function or non-capturing lambda
/// \tparam ReturnT The return type of the function
/// \tparam ArgsT The argument types of the function
template<typename ReturnT, typename...ArgsT>
class function<ReturnT(ArgsT...)> {
public:
	///
	/// \brief default constructor
	constexpr function() noexcept
		: call(nullptr) {
	}

	///
	/// \brief destructor
	constexpr ~function() = default;

	///
	/// \brief copy constructor
	/// \param func the function to copy
	constexpr function(const function& func) noexcept = default;

	///
	/// \brief move constructor
	/// \param func the function to take ownership of
	constexpr function(function&& func) noexcept = default;

	///
	/// \brief function constructor
	/// \param func the function to capture
	constexpr function(ReturnT (*func)(ArgsT...))
		: call(func) {
	}

	///
	/// \brief null constructor
	constexpr function(nullptr_t) noexcept : function() {}

	///
	/// \brief copy assignment
	/// \param func the function to copy
	/// \returns a reference to \emph{this}
	constexpr function& operator=(const function& func) = default;

	///
	/// \brief move assignment
	/// \param func the function to capture
	/// \returns a reference to \emph{this}
	constexpr function& operator=(function&& func) = default;

	///
	/// \brief null assignment
	/// \returns a reference to \emph{this}
	constexpr function& operator=(nullptr_t) {
		call = nullptr;
		return *this;
	}

	///
	/// \brief function assignment
	/// \param func the function to capture
	/// \returns a reference to \emph{this}
	constexpr function& operator=(ReturnT (*func)(ArgsT...)) {
		call = func;
		return *this;
	}

	///
	/// \brief implicit bool check
	/// \returns \emph{true} if a function is captured, \emph{false} otherwise
	constexpr operator bool() const noexcept {
		return call != nullptr;
	}

	///
	/// \brief function call operator
	/// \param args the arguments to call the function with
	/// \returns the result of the function call
	ReturnT operator()(ArgsT...args) const noexcept {
		assertf(call != nullptr, "Attempted to call a null function object!");
		return call(fennec::forward<ArgsT>(args)...);
	}

private:
	ReturnT (*call)(ArgsT&&...) { nullptr };
};

}

#endif // FENNEC_LANG_FUNCTION_H