#ifndef MORE_ADAPTORS_FIRST_N_HPP_
#define MORE_ADAPTORS_FIRST_N_HPP_

#include <boost/iterator/iterator_adaptor.hpp>
#include <boost/range/iterator_range.hpp>

namespace more {

namespace range_detail {

template <class Iterator>
class first_n_iterator : public boost::iterator_adaptor<first_n_iterator<Iterator>,	Iterator>
{
public:

	explicit first_n_iterator(const Iterator& it)
			: first_n_iterator::iterator_adaptor_(it), initial(it), count(0) {}
	first_n_iterator(const Iterator& it, std::size_t n)
			: first_n_iterator::iterator_adaptor_(it), initial(it), count(n) {}

	// using compiler provided copy constructor and copy assignment

private:

	friend class boost::iterator_core_access;

	void increment() { ++(this->base_reference()); ++count; }
	bool equal(first_n_iterator const& other) const
	{
		return this->initial == other.initial && this->count == other.count;
	}

	Iterator initial; // used to be able to differentiate ranges
	std::size_t count;
};

struct first_nd {
	first_nd(std::size_t n) : n(n) {}
	std::size_t n;
};

template<class SinglePassRange>
class first_nd_range
	: public boost::iterator_range< first_n_iterator <
		  typename boost::range_iterator<SinglePassRange>::type> >
{
	typedef boost::iterator_range< first_n_iterator <
		  typename boost::range_iterator<SinglePassRange>::type> > base_t;
public:
	first_nd_range(SinglePassRange& r, std::size_t n)
		: base_t(boost::make_iterator_range(
				first_n_iterator< typename boost::range_iterator<SinglePassRange>::type >
					(r.begin()),
				first_n_iterator< typename boost::range_iterator<SinglePassRange>::type >
					(r.begin(),n)
				))
	{
	}
};

template< class SinglePassRange >
inline first_nd_range<SinglePassRange>
operator|(SinglePassRange& r, const first_nd& f)
{
	return first_nd_range<SinglePassRange>(r, f.n);
}

template< class SinglePassRange >
inline first_nd_range<const SinglePassRange>
operator|(const SinglePassRange& r, const first_nd& f)
{
	return first_nd_range<const SinglePassRange>(r, f.n);
}

}  // namespace range_detail

using range_detail::first_nd_range;

namespace adaptors {

	using range_detail::first_nd;

	template <class SinglePassRange>
	inline first_nd_range<SinglePassRange>
	first_n(SinglePassRange& r, std::size_t n)
	{
		return first_nd_range<SinglePassRange>(r,n);
	}

	template <class SinglePassRange>
	inline first_nd_range<const SinglePassRange>
	first_n(const SinglePassRange& r, std::size_t n)
	{
		return first_nd_range<const SinglePassRange>(r,n);
	}

} // namespace adaptors

} // namespace more


#endif /* MORE_ADAPTORS_FIRST_N_HPP_ */