#ifndef UCS4_ITERATOR_BASE_HPP_INCLUDED
#define UCS4_ITERATOR_BASE_HPP_INCLUDED

#include <iterator>  //input_iterator_tag
#include <utility>   //pair
#include <cstddef>   //ptrdiff_t
#include <cassert>   //assert

#include "unicode_types.hpp"

namespace ucs4
{
	template<typename string_type, typename update_implementation>
	class iterator_base
	{
	public:
		typedef std::input_iterator_tag iterator_category;
		typedef ucs4::char_t value_type;
		typedef ptrdiff_t difference_type;
		typedef ucs4::char_t* pointer;
		typedef ucs4::char_t& reference;

		iterator_base(const string_type& str)
			: current_char(0)
			, string_end(str.end())
			, current_substr(std::make_pair(str.begin(), str.begin()))
		{
			update();
		}

		iterator_base(typename string_type::const_iterator const &begin, typename string_type::const_iterator const &end)
			: current_char(0)
			, string_end(end)
			, current_substr(std::make_pair(begin, begin))
		{
			update();
		}

		static iterator_base begin(const string_type& str)
		{
			return iterator_base(str.begin(), str.end());
		}

		static iterator_base end(const string_type& str)
		{
			return iterator_base(str.end(), str.end());
		}

		bool operator==(const iterator_base& a) const
		{
			return current_substr.first == a.current_substr.first;
		}

		bool operator!=(const iterator_base& a) const
		{ 
			return ! (*this == a); 
		}

		iterator_base& operator++()
		{
			current_substr.first = current_substr.second;
			update();
			return *this;
		}

		ucs4::char_t operator*() const
		{
			return current_char;
		}

		bool next_is_end() const
		{
			if(current_substr.second == string_end)
				return true;
			return false;
		}

		const std::pair<typename string_type::const_iterator, typename string_type::const_iterator>& substr() const
		{
			return current_substr;
		}
	private:
		void update()
		{
			assert(current_substr.first == current_substr.second);
			if(current_substr.first == string_end)
				return;
			current_char = update_implementation::read(current_substr.second, string_end);
		}

		ucs4::char_t current_char;
		typename string_type::const_iterator string_end;
		std::pair<typename string_type::const_iterator, typename string_type::const_iterator> current_substr;
	};

}

#endif