#ifndef SPROUT_CHECKSUM_SUM_HPP
#define SPROUT_CHECKSUM_SUM_HPP

#include <cstddef>
#include <cstdint>
#include <climits>
#include <type_traits>
#include <limits>
#include <sprout/config.hpp>
#include <sprout/container/functions.hpp>
#include <sprout/iterator/operation.hpp>
#include <sprout/iterator/bytes_iterator.hpp>
#include <sprout/numeric/accumulate.hpp>
#include <sprout/detail/integer.hpp>

namespace sprout {
	static_assert(CHAR_BIT == 8, "CHAR_BIT == 8");

	//
	// sum_basic
	//
	template<std::size_t Bits = 8>
	class sum_basic {
		static_assert(Bits % 8 == 0, "Bits % 8 == 0");
	public:
		typedef typename sprout::detail::uint_t<Bits>::least value_type;
		typedef sum_basic const const_type;
		typedef typename std::conditional<
			sizeof(std::size_t) < sizeof(value_type),
			value_type,
			std::size_t
		>::type sum_type;
	private:
		sum_type sum_;
	private:
		template<typename Iterator>
		SPROUT_CONSTEXPR sum_type calc_sum(Iterator first, Iterator last) const {
			return sprout::accumulate(
				sprout::make_bytes_iterator(first),
				sprout::make_bytes_iterator(last),
				sum_
				);
		}
	public:
		SPROUT_CONSTEXPR sum_basic() = default;
		SPROUT_CONSTEXPR sum_basic(sum_basic const&) = default;
		explicit SPROUT_CONSTEXPR sum_basic(sum_type sum)
			: sum_(sum)
		{}
		void reset(sum_type new_sum = 0) {
			sum_ = new_sum;
		}

		SPROUT_CONSTEXPR sum_basic const process_byte(std::uint8_t byte) const {
			return sum_basic(sum_ + byte);
		}
		template<typename Iterator>
		SPROUT_CONSTEXPR sum_basic const process_block(Iterator bytes_begin, Iterator bytes_end) const {
			return sum_basic(calc_sum(bytes_begin, bytes_end));
		}
		template<typename Iterator>
		SPROUT_CONSTEXPR sum_basic const process_bytes(Iterator buffer, std::size_t byte_count) const {
			return process_block(buffer, sprout::next(buffer, byte_count));
		}
		template<typename Range>
		SPROUT_CONSTEXPR sum_basic const process_range(Range const& bytes_range) const {
			return process_block(sprout::begin(bytes_range), sprout::end(bytes_range));
		}

		void process_byte(std::uint8_t byte) {
			sum_ += byte;
		}
		template<typename Iterator>
		void process_block(Iterator bytes_begin, Iterator bytes_end) {
			sum_ = calc_sum(bytes_begin, bytes_end);
		}
		template<typename Iterator>
		void process_bytes(Iterator buffer, std::size_t byte_count) {
			process_block(buffer, sprout::next(buffer, byte_count));
		}
		template<typename Range>
		void process_range(Range const& bytes_range) {
			process_block(sprout::begin(bytes_range), sprout::end(bytes_range));
		}

		SPROUT_CONSTEXPR value_type checksum() const {
			return static_cast<value_type>(sum_ & std::numeric_limits<value_type>::max());
		}
		SPROUT_CONSTEXPR value_type operator()() const {
			return checksum();
		}
	};

	//
	// sum8
	// sum16
	// sum32
	//
	typedef sprout::sum_basic<8> sum8;
	typedef sprout::sum_basic<16> sum16;
	typedef sprout::sum_basic<32> sum32;
}	// namespace sprout

#endif	// #ifndef SPROUT_CHECKSUM_SUM_HPP