// (C) Copyright Jeremy Siek 2001.

// Distributed under the Boost Software License, Version 1.0. (See

// accompanying file LICENSE_1_0.txt or copy at

// http://www.boost.org/LICENSE_1_0.txt)



#ifndef BOOST_SHADOW_ITERATOR_HPP

#define BOOST_SHADOW_ITERATOR_HPP



#include <boost/iterator_adaptors.hpp>

#include <boost/operators.hpp>



namespace boost {



  namespace detail {



    template <class A, class B, class D>

    class shadow_proxy

      : boost::operators< shadow_proxy<A,B,D> >

    {

      typedef shadow_proxy self;

    public:

      inline shadow_proxy(A aa, B bb) : a(aa), b(bb) { }

      inline shadow_proxy(const self& x) : a(x.a), b(x.b) { }

      template <class Self>

      inline shadow_proxy(Self x) : a(x.a), b(x.b) { }

      inline self& operator=(const self& x) { a = x.a; b = x.b; return *this; }

      inline self& operator++() { ++a; return *this; }

      inline self& operator--() { --a; return *this; }

      inline self& operator+=(const self& x) { a += x.a; return *this; }

      inline self& operator-=(const self& x) { a -= x.a; return *this; }

      inline self& operator*=(const self& x) { a *= x.a; return *this; }

      inline self& operator/=(const self& x) { a /= x.a; return *this; }

      inline self& operator%=(const self& x) { return *this; } // JGS

      inline self& operator&=(const self& x) { return *this; } // JGS

      inline self& operator|=(const self& x) { return *this; } // JGS

      inline self& operator^=(const self& x) { return *this; } // JGS

      inline friend D operator-(const self& x, const self& y) {

        return x.a - y.a;

      } 

      inline bool operator==(const self& x) const { return a == x.a;  }

      inline bool operator<(const self& x) const { return a < x.a;  }

      //  protected:

      A a;

      B b;

    };



    struct shadow_iterator_policies

    {

      template <typename iter_pair>

      void initialize(const iter_pair&) { }



      template <typename Iter>

      typename Iter::reference dereference(const Iter& i) const { 

        typedef typename Iter::reference R;

        return R(*i.base().first, *i.base().second); 

      }

      template <typename Iter>

      bool equal(const Iter& p1, const Iter& p2) const { 

        return p1.base().first == p2.base().first;  

      }

      template <typename Iter>

      void increment(Iter& i) { ++i.base().first; ++i.base().second; }



      template <typename Iter>

      void decrement(Iter& i) { --i.base().first; --i.base().second; }



      template <typename Iter>

      bool less(const Iter& x, const Iter& y) const { 

        return x.base().first < y.base().first;  

      }

      template <typename Iter>

      typename Iter::difference_type

      distance(const Iter& x, const Iter& y) const { 

        return y.base().first - x.base().first; 

      }

      template <typename D, typename Iter>

      void advance(Iter& p, D n) { p.base().first += n; p.base().second += n; }

    };



  } // namespace detail



  template <typename IterA, typename IterB>

  struct shadow_iterator_generator {

    

    // To use the iterator_adaptor we can't derive from

    // random_access_iterator because we don't have a real reference.

    // However, we want the STL algorithms to treat the shadow

    // iterator like a random access iterator.

    struct shadow_iterator_tag : public std::input_iterator_tag {

      operator std::random_access_iterator_tag() {

        return std::random_access_iterator_tag();

      };

    };

    typedef typename std::iterator_traits<IterA>::value_type Aval;

    typedef typename std::iterator_traits<IterB>::value_type Bval;

    typedef typename std::iterator_traits<IterA>::reference Aref;

    typedef typename std::iterator_traits<IterB>::reference Bref;

    typedef typename std::iterator_traits<IterA>::difference_type D;

    typedef detail::shadow_proxy<Aval,Bval,Aval> V;

    typedef detail::shadow_proxy<Aref,Bref,Aval> R;

    typedef iterator_adaptor< std::pair<IterA, IterB>,

                              detail::shadow_iterator_policies,

                              V, R, V*, shadow_iterator_tag,

                              D> type;

  };



  // short cut for creating a shadow iterator

  template <class IterA, class IterB>

  inline typename shadow_iterator_generator<IterA,IterB>::type

  make_shadow_iter(IterA a, IterB b) {

    typedef typename shadow_iterator_generator<IterA,IterB>::type Iter;

    return Iter(std::make_pair(a,b)); 

  }



  template <class Cmp>

  struct shadow_cmp {

    inline shadow_cmp(const Cmp& c) : cmp(c) { }

    template <class ShadowProxy1, class ShadowProxy2>

    inline bool operator()(const ShadowProxy1& x, const ShadowProxy2& y) const

    {

      return cmp(x.a, y.a);

    }

    Cmp cmp;

  };



} // namespace boost



namespace std {

  template <class A1, class B1, class D1,

            class A2, class B2, class D2>

  void swap(boost::detail::shadow_proxy<A1&,B1&,D1> x,

            boost::detail::shadow_proxy<A2&,B2&,D2> y)

  {

    std::swap(x.a, y.a);

    std::swap(x.b, y.b);

  }

}



#endif // BOOST_SHADOW_ITERATOR_HPP

