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#ifndef _LIBCUDACXX___MDSPAN_MDSPAN_HPP
#define _LIBCUDACXX___MDSPAN_MDSPAN_HPP

#ifndef __cuda_std__
#include <__config>
#endif // __cuda_std__

#include "../__mdspan/default_accessor.h"
#include "../__mdspan/layout_right.h"
#include "../__mdspan/extents.h"
#include "../__mdspan/compressed_pair.h"
#include "../__type_traits/extent.h"
#include "../__type_traits/is_constructible.h"
#include "../__type_traits/is_convertible.h"
#include "../__type_traits/is_default_constructible.h"
#include "../__type_traits/is_nothrow_constructible.h"
#include "../__type_traits/rank.h"
#include "../__type_traits/remove_cv.h"
#include "../__type_traits/remove_pointer.h"
#include "../__type_traits/remove_reference.h"
#include "../__type_traits/remove_all_extents.h"
#include "../__utility/as_const.h"
#include "../__utility/integer_sequence.h"
#include "../__utility/move.h"
#include "../array"
#include "../span"

#if defined(_CCCL_IMPLICIT_SYSTEM_HEADER_GCC)
#  pragma GCC system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_CLANG)
#  pragma clang system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_MSVC)
#  pragma system_header
#endif // no system header

_LIBCUDACXX_BEGIN_NAMESPACE_STD

#if _LIBCUDACXX_STD_VER > 11

template <
  class _ElementType,
  class _Extents,
  class _LayoutPolicy = layout_right,
  class _AccessorPolicy = default_accessor<_ElementType>
>
class mdspan
{
private:
  static_assert(__detail::__is_extents_v<_Extents>, "mdspan's Extents template parameter must be a specialization of _CUDA_VSTD::extents.");

  // Workaround for non-deducibility of the index sequence template parameter if it's given at the top level
  template <class>
  struct __deduction_workaround;

  template <size_t... _Idxs>
  struct __deduction_workaround<_CUDA_VSTD::index_sequence<_Idxs...>>
  {
    __MDSPAN_FORCE_INLINE_FUNCTION static constexpr
    size_t __size(mdspan const& __self) noexcept {
      return __MDSPAN_FOLD_TIMES_RIGHT((__self.__mapping_ref().extents().template __extent<_Idxs>()), /* * ... * */ size_t(1));
    }
    __MDSPAN_FORCE_INLINE_FUNCTION static constexpr
    bool __empty(mdspan const& __self) noexcept {
      return (__self.rank()>0) && __MDSPAN_FOLD_OR((__self.__mapping_ref().extents().template __extent<_Idxs>()==index_type(0)));
    }
    template <class _ReferenceType, class _SizeType, size_t _Np>
    __MDSPAN_FORCE_INLINE_FUNCTION static constexpr
    _ReferenceType __callop(mdspan const& __self, const _CUDA_VSTD::array<_SizeType, _Np>& __indices) noexcept {
      return __self.__accessor_ref().access(__self.__ptr_ref(), __self.__mapping_ref()(__indices[_Idxs]...));
    }
    template <class _ReferenceType, class _SizeType, size_t _Np>
    __MDSPAN_FORCE_INLINE_FUNCTION static constexpr
    _ReferenceType __callop(mdspan const& __self, const _CUDA_VSTD::span<_SizeType, _Np>& __indices) noexcept {
      return __self.__accessor_ref().access(__self.__ptr_ref(), __self.__mapping_ref()(__indices[_Idxs]...));
    }
  };

public:

  //--------------------------------------------------------------------------------
  // Domain and codomain types

  using extents_type = _Extents;
  using layout_type = _LayoutPolicy;
  using accessor_type = _AccessorPolicy;
  using mapping_type = typename layout_type::template mapping<extents_type>;
  using element_type = _ElementType;
  using value_type = _CUDA_VSTD::remove_cv_t<element_type>;
  using index_type = typename extents_type::index_type;
  using size_type = typename extents_type::size_type;
  using rank_type = typename extents_type::rank_type;
  using data_handle_type = typename accessor_type::data_handle_type;
  using reference = typename accessor_type::reference;

  __MDSPAN_INLINE_FUNCTION static constexpr size_t rank() noexcept { return extents_type::rank(); }
  __MDSPAN_INLINE_FUNCTION static constexpr size_t rank_dynamic() noexcept { return extents_type::rank_dynamic(); }
  __MDSPAN_INLINE_FUNCTION static constexpr size_t static_extent(size_t __r) noexcept { return extents_type::static_extent(__r); }
  __MDSPAN_INLINE_FUNCTION constexpr index_type extent(size_t __r) const noexcept { return __mapping_ref().extents().extent(__r); };

private:

  // Can't use defaulted parameter in the __deduction_workaround template because of a bug in MSVC warning C4348.
  using __impl = __deduction_workaround<_CUDA_VSTD::make_index_sequence<extents_type::rank()>>;

  using __map_acc_pair_t = __detail::__compressed_pair<mapping_type, accessor_type>;

public:

  //--------------------------------------------------------------------------------
  // [mdspan.basic.cons], mdspan constructors, assignment, and destructor

#if !__MDSPAN_HAS_CXX_20
  __MDSPAN_INLINE_FUNCTION_DEFAULTED constexpr mdspan() = default;
#else
  __MDSPAN_INLINE_FUNCTION_DEFAULTED constexpr mdspan()
    requires(
       // Directly using rank_dynamic()>0 here doesn't work for nvcc
       (extents_type::rank_dynamic() >0) &&
       _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_default_constructible, data_handle_type) &&
       _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_default_constructible, mapping_type) &&
       _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_default_constructible, accessor_type)
     ) = default;
#endif
  __MDSPAN_INLINE_FUNCTION_DEFAULTED constexpr mdspan(const mdspan&) = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED constexpr mdspan(mdspan&&) = default;

  __MDSPAN_TEMPLATE_REQUIRES(
    class... _SizeTypes,
    /* requires */ (
      __MDSPAN_FOLD_AND(_LIBCUDACXX_TRAIT(_CUDA_VSTD::is_convertible, _SizeTypes, index_type) /* && ... */) &&
      __MDSPAN_FOLD_AND(_LIBCUDACXX_TRAIT(_CUDA_VSTD::is_nothrow_constructible, index_type, _SizeTypes) /* && ... */) &&
      ((sizeof...(_SizeTypes) == rank()) || (sizeof...(_SizeTypes) == rank_dynamic())) &&
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_constructible, mapping_type, extents_type) &&
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_default_constructible, accessor_type)
    )
  )
  __MDSPAN_INLINE_FUNCTION
  explicit constexpr mdspan(data_handle_type __p, _SizeTypes... __dynamic_extents)
    // TODO @proposal-bug shouldn't I be allowed to do `move(__p)` here?
    : __members(_CUDA_VSTD::move(__p), __map_acc_pair_t(mapping_type(extents_type(static_cast<index_type>(_CUDA_VSTD::move(__dynamic_extents))...)), accessor_type()))
  { }

  __MDSPAN_TEMPLATE_REQUIRES(
    class _SizeType, size_t _Np,
    /* requires */ (
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_convertible, _SizeType, index_type) &&
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_nothrow_constructible, index_type, _SizeType) &&
      ((_Np == rank()) || (_Np == rank_dynamic())) &&
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_constructible, mapping_type, extents_type) &&
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_default_constructible, accessor_type)
    )
  )
  __MDSPAN_CONDITIONAL_EXPLICIT(_Np != rank_dynamic())
  __MDSPAN_INLINE_FUNCTION
  constexpr mdspan(data_handle_type __p, const _CUDA_VSTD::array<_SizeType, _Np>& __dynamic_extents)
    : __members(_CUDA_VSTD::move(__p), __map_acc_pair_t(mapping_type(extents_type(__dynamic_extents)), accessor_type()))
  { }

  __MDSPAN_TEMPLATE_REQUIRES(
    class _SizeType, size_t _Np,
    /* requires */ (
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_convertible, _SizeType, index_type) &&
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_nothrow_constructible, index_type, _SizeType) &&
      ((_Np == rank()) || (_Np == rank_dynamic())) &&
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_constructible, mapping_type, extents_type) &&
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_default_constructible, accessor_type)
    )
  )
  __MDSPAN_CONDITIONAL_EXPLICIT(_Np != rank_dynamic())
  __MDSPAN_INLINE_FUNCTION
  constexpr mdspan(data_handle_type __p, _CUDA_VSTD::span<_SizeType, _Np> __dynamic_extents)
    : __members(_CUDA_VSTD::move(__p), __map_acc_pair_t(mapping_type(extents_type(_CUDA_VSTD::as_const(__dynamic_extents))), accessor_type()))
  { }

  __MDSPAN_FUNCTION_REQUIRES(
    (__MDSPAN_INLINE_FUNCTION constexpr),
    mdspan, (data_handle_type __p, const extents_type& __exts), ,
    /* requires */ (_LIBCUDACXX_TRAIT(_CUDA_VSTD::is_default_constructible, accessor_type) &&
                    _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_constructible, mapping_type, extents_type))
  ) : __members(_CUDA_VSTD::move(__p), __map_acc_pair_t(mapping_type(__exts), accessor_type()))
  { }

  __MDSPAN_FUNCTION_REQUIRES(
    (__MDSPAN_INLINE_FUNCTION constexpr),
    mdspan, (data_handle_type __p, const mapping_type& __m), ,
    /* requires */ (_LIBCUDACXX_TRAIT(_CUDA_VSTD::is_default_constructible, accessor_type))
  ) : __members(_CUDA_VSTD::move(__p), __map_acc_pair_t(__m, accessor_type()))
  { }

  __MDSPAN_INLINE_FUNCTION
  constexpr mdspan(data_handle_type __p, const mapping_type& __m, const accessor_type& __a)
    : __members(_CUDA_VSTD::move(__p), __map_acc_pair_t(__m, __a))
  { }

  __MDSPAN_TEMPLATE_REQUIRES(
    class _OtherElementType, class _OtherExtents, class _OtherLayoutPolicy, class _OtherAccessor,
    /* requires */ (
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_constructible, mapping_type, typename _OtherLayoutPolicy::template mapping<_OtherExtents>) &&
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_constructible, accessor_type, _OtherAccessor)
    )
  )
  __MDSPAN_INLINE_FUNCTION
  constexpr mdspan(const mdspan<_OtherElementType, _OtherExtents, _OtherLayoutPolicy, _OtherAccessor>& __other)
    : __members(__other.__ptr_ref(), __map_acc_pair_t(__other.__mapping_ref(), __other.__accessor_ref()))
  {
      static_assert(_LIBCUDACXX_TRAIT(_CUDA_VSTD::is_constructible, data_handle_type, typename _OtherAccessor::data_handle_type),"Incompatible data_handle_type for mdspan construction");
      static_assert(_LIBCUDACXX_TRAIT(_CUDA_VSTD::is_constructible, extents_type, _OtherExtents),"Incompatible extents for mdspan construction");
      /*
       * TODO: Check precondition
       * For each rank index __r of extents_type, static_extent(__r) == dynamic_extent || static_extent(__r) == __other.extent(__r) is true.
       */
  }

  /* Might need this on NVIDIA?
  __MDSPAN_INLINE_FUNCTION_DEFAULTED
  ~mdspan() = default;
  */

  __MDSPAN_INLINE_FUNCTION_DEFAULTED __MDSPAN_CONSTEXPR_14_DEFAULTED mdspan& operator=(const mdspan&) = default;
  __MDSPAN_INLINE_FUNCTION_DEFAULTED __MDSPAN_CONSTEXPR_14_DEFAULTED mdspan& operator=(mdspan&&) = default;


  //--------------------------------------------------------------------------------
  // [mdspan.basic.mapping], mdspan mapping domain multidimensional index to access codomain element

  #if __MDSPAN_USE_BRACKET_OPERATOR
  __MDSPAN_TEMPLATE_REQUIRES(
    class... _SizeTypes,
    /* requires */ (
      __MDSPAN_FOLD_AND(_LIBCUDACXX_TRAIT(_CUDA_VSTD::is_convertible, _SizeTypes, index_type) /* && ... */) &&
      __MDSPAN_FOLD_AND(_LIBCUDACXX_TRAIT(_CUDA_VSTD::is_nothrow_constructible, index_type, _SizeTypes) /* && ... */) &&
      (rank() == sizeof...(_SizeTypes))
    )
  )
  __MDSPAN_FORCE_INLINE_FUNCTION
  constexpr reference operator[](_SizeTypes... __indices) const
  {
    return __accessor_ref().access(__ptr_ref(), __mapping_ref()(index_type(__indices)...));
  }
  #endif

  __MDSPAN_TEMPLATE_REQUIRES(
    class _SizeType,
    /* requires */ (
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_convertible, _SizeType, index_type) &&
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_nothrow_constructible, index_type, _SizeType)
    )
  )
  __MDSPAN_FORCE_INLINE_FUNCTION
  constexpr reference operator[](const _CUDA_VSTD::array<_SizeType, rank()>& __indices) const
  {
    return __impl::template __callop<reference>(*this, __indices);
  }

  __MDSPAN_TEMPLATE_REQUIRES(
    class _SizeType,
    /* requires */ (
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_convertible, _SizeType, index_type) &&
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_nothrow_constructible, index_type, _SizeType)
    )
  )
  __MDSPAN_FORCE_INLINE_FUNCTION
  constexpr reference operator[](_CUDA_VSTD::span<_SizeType, rank()> __indices) const
  {
    return __impl::template __callop<reference>(*this, __indices);
  }

  #if !__MDSPAN_USE_BRACKET_OPERATOR
  __MDSPAN_TEMPLATE_REQUIRES(
    class _Index,
    /* requires */ (
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_convertible, _Index, index_type) &&
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_nothrow_constructible, index_type, _Index) &&
      extents_type::rank() == 1
    )
  )
  __MDSPAN_FORCE_INLINE_FUNCTION
  constexpr reference operator[](_Index __idx) const
  {
    return __accessor_ref().access(__ptr_ref(), __mapping_ref()(index_type(__idx)));
  }
  #endif

  #if __MDSPAN_USE_PAREN_OPERATOR
  __MDSPAN_TEMPLATE_REQUIRES(
    class... _SizeTypes,
    /* requires */ (
      __MDSPAN_FOLD_AND(_LIBCUDACXX_TRAIT(_CUDA_VSTD::is_convertible, _SizeTypes, index_type) /* && ... */) &&
      __MDSPAN_FOLD_AND(_LIBCUDACXX_TRAIT(_CUDA_VSTD::is_nothrow_constructible, index_type, _SizeTypes) /* && ... */) &&
      extents_type::rank() == sizeof...(_SizeTypes)
    )
  )
  __MDSPAN_FORCE_INLINE_FUNCTION
  constexpr reference operator()(_SizeTypes... __indices) const
  {
    return __accessor_ref().access(__ptr_ref(), __mapping_ref()(__indices...));
  }

  __MDSPAN_TEMPLATE_REQUIRES(
    class _SizeType,
    /* requires */ (
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_convertible, _SizeType, index_type) &&
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_nothrow_constructible, index_type, _SizeType)
    )
  )
  __MDSPAN_FORCE_INLINE_FUNCTION
  constexpr reference operator()(const _CUDA_VSTD::array<_SizeType, rank()>& __indices) const
  {
    return __impl::template __callop<reference>(*this, __indices);
  }

  __MDSPAN_TEMPLATE_REQUIRES(
    class _SizeType,
    /* requires */ (
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_convertible, _SizeType, index_type) &&
      _LIBCUDACXX_TRAIT(_CUDA_VSTD::is_nothrow_constructible, index_type, _SizeType)
    )
  )
  __MDSPAN_FORCE_INLINE_FUNCTION
  constexpr reference operator()(_CUDA_VSTD::span<_SizeType, rank()> __indices) const
  {
    return __impl::template __callop<reference>(*this, __indices);
  }
  #endif // __MDSPAN_USE_PAREN_OPERATOR

  __MDSPAN_INLINE_FUNCTION constexpr size_t size() const noexcept {
    return __impl::__size(*this);
  };

  __MDSPAN_INLINE_FUNCTION constexpr bool empty() const noexcept {
    return __impl::__empty(*this);
  };

  __MDSPAN_INLINE_FUNCTION
  friend constexpr void swap(mdspan& __x, mdspan& __y) noexcept {
    swap(__x.__ptr_ref(), __y.__ptr_ref());
    swap(__x.__mapping_ref(), __y.__mapping_ref());
    swap(__x.__accessor_ref(), __y.__accessor_ref());
  }

  //--------------------------------------------------------------------------------
  // [mdspan.basic.domobs], mdspan observers of the domain multidimensional index space


  __MDSPAN_INLINE_FUNCTION constexpr const extents_type& extents() const noexcept { return __mapping_ref().extents(); };
  __MDSPAN_INLINE_FUNCTION constexpr const data_handle_type& data_handle() const noexcept { return __ptr_ref(); };
  __MDSPAN_INLINE_FUNCTION constexpr const mapping_type& mapping() const noexcept { return __mapping_ref(); };
  __MDSPAN_INLINE_FUNCTION constexpr const accessor_type& accessor() const noexcept { return __accessor_ref(); };

  //--------------------------------------------------------------------------------
  // [mdspan.basic.obs], mdspan observers of the mapping

  __MDSPAN_INLINE_FUNCTION static constexpr bool is_always_unique() noexcept { return mapping_type::is_always_unique(); };
  __MDSPAN_INLINE_FUNCTION static constexpr bool is_always_exhaustive() noexcept { return mapping_type::is_always_exhaustive(); };
  __MDSPAN_INLINE_FUNCTION static constexpr bool is_always_strided() noexcept { return mapping_type::is_always_strided(); };

  __MDSPAN_INLINE_FUNCTION constexpr bool is_unique() const noexcept { return __mapping_ref().is_unique(); };
  __MDSPAN_INLINE_FUNCTION constexpr bool is_exhaustive() const noexcept { return __mapping_ref().is_exhaustive(); };
  __MDSPAN_INLINE_FUNCTION constexpr bool is_strided() const noexcept { return __mapping_ref().is_strided(); };
  __MDSPAN_INLINE_FUNCTION constexpr index_type stride(size_t __r) const { return __mapping_ref().stride(__r); };

private:

  __detail::__compressed_pair<data_handle_type, __map_acc_pair_t> __members{};

  __MDSPAN_FORCE_INLINE_FUNCTION constexpr data_handle_type& __ptr_ref() noexcept { return __members.__first(); }
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr data_handle_type const& __ptr_ref() const noexcept { return __members.__first(); }
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr mapping_type& __mapping_ref() noexcept { return __members.__second().__first(); }
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr mapping_type const& __mapping_ref() const noexcept { return __members.__second().__first(); }
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr accessor_type& __accessor_ref() noexcept { return __members.__second().__second(); }
  __MDSPAN_FORCE_INLINE_FUNCTION constexpr accessor_type const& __accessor_ref() const noexcept { return __members.__second().__second(); }

  template <class, class, class, class>
  friend class mdspan;

};

#if defined(__MDSPAN_USE_CLASS_TEMPLATE_ARGUMENT_DEDUCTION)
__MDSPAN_TEMPLATE_REQUIRES(
  class _ElementType, class... _SizeTypes,
  /* requires */ __MDSPAN_FOLD_AND(_LIBCUDACXX_TRAIT(is_integral, _SizeTypes) /* && ... */) &&
  (sizeof...(_SizeTypes) > 0)
)
_LIBCUDACXX_HOST_DEVICE explicit mdspan(_ElementType*, _SizeTypes...)
  -> mdspan<_ElementType, dextents<size_t, sizeof...(_SizeTypes)>>;

__MDSPAN_TEMPLATE_REQUIRES(
  class _Pointer,
  (_LIBCUDACXX_TRAIT(is_pointer, _CUDA_VSTD::remove_reference_t<_Pointer>))
)
_LIBCUDACXX_HOST_DEVICE  mdspan(_Pointer&&) -> mdspan<_CUDA_VSTD::remove_pointer_t<_CUDA_VSTD::remove_reference_t<_Pointer>>, extents<size_t>>;
__MDSPAN_TEMPLATE_REQUIRES(
  class _CArray,
  (_LIBCUDACXX_TRAIT(is_array, _CArray) && (rank_v<_CArray> == 1))
)
_LIBCUDACXX_HOST_DEVICE mdspan(_CArray&) -> mdspan<_CUDA_VSTD::remove_all_extents_t<_CArray>, extents<size_t, _CUDA_VSTD::extent_v<_CArray,0>>>;

template <class _ElementType, class _SizeType, size_t _Np>
_LIBCUDACXX_HOST_DEVICE mdspan(_ElementType*, const _CUDA_VSTD::array<_SizeType, _Np>&)
  -> mdspan<_ElementType, dextents<size_t, _Np>>;

template <class _ElementType, class _SizeType, size_t _Np>
_LIBCUDACXX_HOST_DEVICE mdspan(_ElementType*, _CUDA_VSTD::span<_SizeType, _Np>)
  -> mdspan<_ElementType, dextents<size_t, _Np>>;

// This one is necessary because all the constructors take `data_handle_type`s, not
// `_ElementType*`s, and `data_handle_type` is taken from `accessor_type::data_handle_type`, which
// seems to throw off automatic deduction guides.
template <class _ElementType, class _SizeType, size_t... _ExtentsPack>
_LIBCUDACXX_HOST_DEVICE mdspan(_ElementType*, const extents<_SizeType, _ExtentsPack...>&)
  -> mdspan<_ElementType, extents<_SizeType, _ExtentsPack...>>;

template <class _ElementType, class _MappingType>
_LIBCUDACXX_HOST_DEVICE mdspan(_ElementType*, const _MappingType&)
  -> mdspan<_ElementType, typename _MappingType::extents_type, typename _MappingType::layout_type>;

template <class _MappingType, class _AccessorType>
_LIBCUDACXX_HOST_DEVICE mdspan(const typename _AccessorType::data_handle_type, const _MappingType&, const _AccessorType&)
  -> mdspan<typename _AccessorType::element_type, typename _MappingType::extents_type, typename _MappingType::layout_type, _AccessorType>;
#endif

#endif // _LIBCUDACXX_STD_VER > 11

_LIBCUDACXX_END_NAMESPACE_STD

#endif // _LIBCUDACXX___MDSPAN_MDSPAN_HPP