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//                        Kokkos v. 2.0
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#ifndef KOKKOS_KOKKOS_EXTENTS_HPP
#define KOKKOS_KOKKOS_EXTENTS_HPP

#include <cstddef>

namespace Kokkos {
namespace Experimental {

constexpr ptrdiff_t dynamic_extent = -1;

template <ptrdiff_t... ExtentSpecs>
struct Extents {
  /* TODO @enhancement flesh this out more */
};

template <class Exts, ptrdiff_t NewExtent>
struct PrependExtent;

template <ptrdiff_t... Exts, ptrdiff_t NewExtent>
struct PrependExtent<
  Extents<Exts...>, NewExtent
> {
  using type = Extents<NewExtent, Exts...>;
};

template <class Exts, ptrdiff_t NewExtent>
struct AppendExtent;

template <ptrdiff_t... Exts, ptrdiff_t NewExtent>
struct AppendExtent<
  Extents<Exts...>, NewExtent
> {
  using type = Extents<Exts..., NewExtent>;
};

} // end namespace Experimental

namespace Impl {

namespace _parse_view_extents_impl {

template <class T>
struct _all_remaining_extents_dynamic : std::true_type { };

template <class T>
struct _all_remaining_extents_dynamic<T*>
  : _all_remaining_extents_dynamic<T>
{ };

template <class T, unsigned N>
struct _all_remaining_extents_dynamic<T[N]>
  : std::false_type
{ };

template <class T, class Result, class=void>
struct _parse_impl {
  using type = Result;
};

// We have to treat the case of int**[x] specially, since it *doesn't* go backwards
template <class T, ptrdiff_t... ExtentSpec>
struct _parse_impl<
  T*, Experimental::Extents<ExtentSpec...>,
  typename std::enable_if<_all_remaining_extents_dynamic<T>::value>::type
>
  : _parse_impl<
      T, Experimental::Extents<Experimental::dynamic_extent, ExtentSpec...>
    >
{ };

// int*(*[x])[y] should still work also (meaning int[][x][][y])
template <class T, ptrdiff_t... ExtentSpec>
struct _parse_impl<
  T*, Experimental::Extents<ExtentSpec...>,
  typename std::enable_if<not _all_remaining_extents_dynamic<T>::value>::type
>
{
  using _next = Kokkos::Experimental::AppendExtent<
    typename _parse_impl<T, Experimental::Extents<ExtentSpec...>, void>::type,
    Experimental::dynamic_extent
  >;
  using type = typename _next::type;
};

template <class T, ptrdiff_t... ExtentSpec, unsigned N>
struct _parse_impl<
  T[N], Experimental::Extents<ExtentSpec...>, void
>
  : _parse_impl<
      T, Experimental::Extents<ExtentSpec..., ptrdiff_t(N)> // TODO @pedantic this could be a narrowing cast
    >
{ };

} // end namespace _parse_view_extents_impl

template <class DataType>
struct ParseViewExtents {
  using type =
    typename _parse_view_extents_impl
      ::_parse_impl<DataType, Experimental::Extents<>>::type;
};

template <class ValueType, ptrdiff_t Ext>
struct ApplyExtent
{
  using type = ValueType[Ext];
};

template <class ValueType>
struct ApplyExtent<ValueType, Experimental::dynamic_extent>
{
  using type = ValueType*;
};

template <class ValueType, unsigned N, ptrdiff_t Ext>
struct ApplyExtent<ValueType[N], Ext>
{
  using type = typename ApplyExtent<ValueType, Ext>::type[N];
};

template <class ValueType, ptrdiff_t Ext>
struct ApplyExtent<ValueType*, Ext>
{
  using type = ValueType*[Ext];
};

template <class ValueType>
struct ApplyExtent<ValueType*, Experimental::dynamic_extent>
{
  using type = typename ApplyExtent<ValueType, Experimental::dynamic_extent>::type*;
};

template <class ValueType, unsigned N>
struct ApplyExtent<ValueType[N], Experimental::dynamic_extent>
{
  using type = typename ApplyExtent<ValueType, Experimental::dynamic_extent>::type[N];
};

} // end namespace Impl

} // end namespace Kokkos

#endif //KOKKOS_KOKKOS_EXTENTS_HPP
