/* Copyright 2016-2017 Joaquin M Lopez Munoz.
 * 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)
 *
 * See http://www.boost.org/libs/poly_collection for library home page.
 */

#ifndef BOOST_POLY_COLLECTION_DETAIL_STRIDE_ITERATOR_HPP
#define BOOST_POLY_COLLECTION_DETAIL_STRIDE_ITERATOR_HPP

#if defined(_MSC_VER)
#pragma once
#endif

#include <boost/iterator/iterator_facade.hpp>
#include <type_traits>

namespace boost{

namespace poly_collection{

namespace detail{

/* random-access iterator to Value elements laid out stride *chars* apart */

template<typename Value>
class stride_iterator:
  public boost::iterator_facade<
    stride_iterator<Value>,
    Value,
    boost::random_access_traversal_tag
  >
{
public:
  stride_iterator()=default;
  stride_iterator(Value* p,std::size_t stride)noexcept:p{p},stride_{stride}{}
  stride_iterator(const stride_iterator&)=default;
  stride_iterator& operator=(const stride_iterator&)=default;

  template<
    typename NonConstValue,
    typename std::enable_if<
      std::is_same<Value,const NonConstValue>::value>::type* =nullptr
  >
  stride_iterator(const stride_iterator<NonConstValue>& x)noexcept:
    p{x.p},stride_{x.stride_}{}

  template<
    typename NonConstValue,
    typename std::enable_if<
      std::is_same<Value,const NonConstValue>::value>::type* =nullptr
  >
  stride_iterator& operator=(const stride_iterator<NonConstValue>& x)noexcept
  {
    p=x.p;stride_=x.stride_;
    return *this;
  }

  /* interoperability with [Derived]Value* */

  stride_iterator& operator=(Value* p_)noexcept{p=p_;return *this;}
  operator Value*()const noexcept{return p;}

  template<
    typename DerivedValue,
    typename std::enable_if<
      std::is_base_of<Value,DerivedValue>::value&&
      (std::is_const<Value>::value||!std::is_const<DerivedValue>::value)
    >::type* =nullptr
  >
  explicit stride_iterator(DerivedValue* x)noexcept:
    p{x},stride_{sizeof(DerivedValue)}{}

  template<
    typename DerivedValue,
    typename std::enable_if<
      std::is_base_of<Value,DerivedValue>::value&&
      (!std::is_const<Value>::value||std::is_const<DerivedValue>::value)
    >::type* =nullptr
  >
  explicit operator DerivedValue*()const noexcept
  {return static_cast<DerivedValue*>(p);}

  std::size_t stride()const noexcept{return stride_;}

private:
  template<typename>
  friend class stride_iterator;

  using char_pointer=typename std::conditional<
    std::is_const<Value>::value,
    const char*,
    char*
  >::type;

  static char_pointer char_ptr(Value* p)noexcept
    {return reinterpret_cast<char_pointer>(p);}
  static Value*       value_ptr(char_pointer p)noexcept
    {return reinterpret_cast<Value*>(p);}

  friend class boost::iterator_core_access;

  Value& dereference()const noexcept{return *p;}
  bool equal(const stride_iterator& x)const noexcept{return p==x.p;}
  void increment()noexcept{p=value_ptr(char_ptr(p)+stride_);}
  void decrement()noexcept{p=value_ptr(char_ptr(p)-stride_);}
  template<typename Integral>
  void advance(Integral n)noexcept
    {p=value_ptr(char_ptr(p)+n*(std::ptrdiff_t)stride_);}
  std::ptrdiff_t distance_to(const stride_iterator& x)const noexcept
    {return (char_ptr(x.p)-char_ptr(p))/(std::ptrdiff_t)stride_;}          

  Value*      p;
  std::size_t stride_;
};

} /* namespace poly_collection::detail */

} /* namespace poly_collection */

} /* namespace boost */

#endif
