/**
	This file is a part of rexy's general purpose library
	Copyright (C) 2020 rexy712

	This program is free software: you can redistribute it and/or modify
	it under the terms of the GNU Affero 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 Affero General Public License for more details.

	You should have received a copy of the GNU Affero General Public License
	along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#ifndef REXY_CX_ALGORITHM_HPP
#define REXY_CX_ALGORITHM_HPP

#include "utility.hpp" //swap

#include <type_traits>

namespace rexy::cx{

	template<class Iter, class Compare>
	constexpr Iter qs_partition(Iter left, Iter right, const Compare& cmp)
		noexcept(std::is_nothrow_invocable<Compare,decltype(*left),decltype(*right)>::value &&
		         noexcept(cx::swap(*left,*right)))
	{
		auto range = right - left;
		auto pivot = left + (range / 2);
		auto value = *pivot;

		//move pivot value all the way to the right side to preserve it
		cx::swap(*pivot, *right);
		for(auto it = left;it != right;++it){
			if(cmp(*it, value)){
				cx::swap(*left, *it);
				++left;
			}
		}
		//move pivot value back to proper position
		cx::swap(*left, *right);
		return left;
	}
	template<class Iter, class Compare>
	constexpr void quicksort(Iter left, Iter right, const Compare& cmp)
		noexcept(noexcept(cx::qs_partition(left, right, cmp)))
	{
		while(left < right){
			auto real_right = right-1;
			auto pivot = qs_partition(left, real_right, cmp);
			quicksort(left, pivot, cmp);
			left = ++pivot;
		}
	}

}

#endif