/**
	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 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 <http://www.gnu.org/licenses/>.
*/

#ifndef REXY_DETAIL_ALGORITHM_HPP
#define REXY_DETAIL_ALGORITHM_HPP

#include "../utility.hpp" //swap

#include <type_traits> //nothrow_invocable
#include <utility> //pair, forward
#include <iterator> //iterator_traits
#include <cstddef> //size_t

namespace rexy::detail{

	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(::rexy::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
		::rexy::swap(*pivot, *right);
		for(auto it = left;it != right;++it){
			if(cmp(*it, value)){
				::rexy::swap(*left, *it);
				++left;
			}
		}
		//move pivot value back to proper position
		::rexy::swap(*left, *right);
		return left;
	}
	template<class Iter, class Op>
	constexpr std::pair<std::size_t,size_t> max_suffix(const Iter& needle, std::size_t nlen, const Op& op = Op()){
		using value_type = typename std::iterator_traits<Iter>::value_type;
		std::size_t max_suffix = -1;
		std::size_t j = 0;
		std::size_t k = 1;
		std::size_t period = 1;
		value_type a;
		value_type b;

		while(j + k < nlen){
			a = needle[j + k];
			b = needle[max_suffix + k];
			if(op(a, b)){
				j += k;
				k = 1;
				period = j - max_suffix;
			}else if(a == b){
				if(k != period){
					++k;
				}else{
					j += period;
					k = 1;
				}
			}else{
				max_suffix = j++;
				k = period = 1;
			}
		}
		return {max_suffix, period};
	}

	template<class Iter>
	constexpr std::pair<std::size_t,size_t> critical_factorization(const Iter& nstart, const Iter& nend){
		auto msuffix = max_suffix(nstart, nend - nstart, []<class T, class U>(T&& left, U&& right) constexpr{
			return std::forward<T>(left) < std::forward<U>(right);
		});
		auto msuffix_rev = max_suffix(nstart, nend - nstart, []<class T, class U>(T&& left, U&& right) constexpr{
			return std::forward<T>(left) > std::forward<U>(right);
		});
		if(msuffix.first < msuffix_rev.first){
			return msuffix_rev;
		}
		return msuffix;
	}
	template<class Iter>
	constexpr bool iter_compare(const Iter& left, const Iter& right, std::size_t length){
		for(std::size_t i = 0;i < length;++i){
			if(left[i] != right[i])
				return false;
		}
		return true;
	}

}

#endif