// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef _LIBCPP___RANGES_SUBRANGE_H
#define _LIBCPP___RANGES_SUBRANGE_H

#include <__concepts/constructible.h>
#include <__concepts/convertible_to.h>
#include <__concepts/copyable.h>
#include <__concepts/derived_from.h>
#include <__concepts/different_from.h>
#include <__config>
#include <__debug>
#include <__iterator/advance.h>
#include <__iterator/concepts.h>
#include <__iterator/incrementable_traits.h>
#include <__iterator/iterator_traits.h>
#include <__ranges/access.h>
#include <__ranges/concepts.h>
#include <__ranges/dangling.h>
#include <__ranges/enable_borrowed_range.h>
#include <__ranges/size.h>
#include <__ranges/view_interface.h>
#include <__tuple>
#include <__utility/move.h>
#include <type_traits>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#pragma GCC system_header
#endif

_LIBCPP_BEGIN_NAMESPACE_STD

#if !defined(_LIBCPP_HAS_NO_RANGES)

namespace ranges {
  template<class _From, class _To>
  concept __convertible_to_non_slicing =
    convertible_to<_From, _To> &&
    // If they're both pointers, they must have the same element type.
    !(is_pointer_v<decay_t<_From>> &&
      is_pointer_v<decay_t<_To>> &&
      __different_from<remove_pointer_t<decay_t<_From>>, remove_pointer_t<decay_t<_To>>>);

  template<class _Tp>
  concept __pair_like =
    !is_reference_v<_Tp> && requires(_Tp __t) {
      typename tuple_size<_Tp>::type; // Ensures `tuple_size<T>` is complete.
      requires derived_from<tuple_size<_Tp>, integral_constant<size_t, 2>>;
      typename tuple_element_t<0, remove_const_t<_Tp>>;
      typename tuple_element_t<1, remove_const_t<_Tp>>;
      { _VSTD::get<0>(__t) } -> convertible_to<const tuple_element_t<0, _Tp>&>;
      { _VSTD::get<1>(__t) } -> convertible_to<const tuple_element_t<1, _Tp>&>;
    };

  template<class _Pair, class _Iter, class _Sent>
  concept __pair_like_convertible_from =
    !range<_Pair> && __pair_like<_Pair> &&
    constructible_from<_Pair, _Iter, _Sent> &&
    __convertible_to_non_slicing<_Iter, tuple_element_t<0, _Pair>> &&
    convertible_to<_Sent, tuple_element_t<1, _Pair>>;

  enum class _LIBCPP_ENUM_VIS subrange_kind : bool { unsized, sized };

  template<input_or_output_iterator _Iter, sentinel_for<_Iter> _Sent = _Iter,
           subrange_kind _Kind = sized_sentinel_for<_Sent, _Iter>
             ? subrange_kind::sized
             : subrange_kind::unsized>
    requires (_Kind == subrange_kind::sized || !sized_sentinel_for<_Sent, _Iter>)
  class _LIBCPP_TEMPLATE_VIS subrange
    : public view_interface<subrange<_Iter, _Sent, _Kind>>
  {
  private:
    static constexpr bool _StoreSize = (_Kind == subrange_kind::sized && !sized_sentinel_for<_Sent, _Iter>);
    static constexpr bool _MustProvideSizeAtConstruction = !_StoreSize; // just to improve compiler diagnostics
    struct _Empty { constexpr _Empty(auto) noexcept { } };
    using _Size = conditional_t<_StoreSize, make_unsigned_t<iter_difference_t<_Iter>>, _Empty>;
    [[no_unique_address]] _Iter __begin_ = _Iter();
    [[no_unique_address]] _Sent __end_ = _Sent();
    [[no_unique_address]] _Size __size_ = 0;

  public:
    _LIBCPP_HIDE_FROM_ABI
    subrange() requires default_initializable<_Iter> = default;

    _LIBCPP_HIDE_FROM_ABI
    constexpr subrange(__convertible_to_non_slicing<_Iter> auto __iter, _Sent __sent)
      requires _MustProvideSizeAtConstruction
      : __begin_(_VSTD::move(__iter)), __end_(std::move(__sent))
    { }

    _LIBCPP_HIDE_FROM_ABI
    constexpr subrange(__convertible_to_non_slicing<_Iter> auto __iter, _Sent __sent,
                       make_unsigned_t<iter_difference_t<_Iter>> __n)
      requires (_Kind == subrange_kind::sized)
      : __begin_(_VSTD::move(__iter)), __end_(std::move(__sent)), __size_(__n)
    {
      if constexpr (sized_sentinel_for<_Sent, _Iter>)
        _LIBCPP_ASSERT((__end_ - __begin_) == static_cast<iter_difference_t<_Iter>>(__n),
          "std::ranges::subrange was passed an invalid size hint");
    }

    template<__different_from<subrange> _Range>
      requires borrowed_range<_Range> &&
               __convertible_to_non_slicing<iterator_t<_Range>, _Iter> &&
               convertible_to<sentinel_t<_Range>, _Sent>
    _LIBCPP_HIDE_FROM_ABI
    constexpr subrange(_Range&& __range)
      requires (!_StoreSize)
      : subrange(ranges::begin(__range), ranges::end(__range))
    { }

    template<__different_from<subrange> _Range>
      requires borrowed_range<_Range> &&
               __convertible_to_non_slicing<iterator_t<_Range>, _Iter> &&
               convertible_to<sentinel_t<_Range>, _Sent>
    _LIBCPP_HIDE_FROM_ABI
    constexpr subrange(_Range&& __range)
      requires _StoreSize && sized_range<_Range>
      : subrange(__range, ranges::size(__range))
    { }

    template<borrowed_range _Range>
      requires __convertible_to_non_slicing<iterator_t<_Range>, _Iter> &&
               convertible_to<sentinel_t<_Range>, _Sent>
    _LIBCPP_HIDE_FROM_ABI
    constexpr subrange(_Range&& __range, make_unsigned_t<iter_difference_t<_Iter>> __n)
      requires (_Kind == subrange_kind::sized)
      : subrange(ranges::begin(__range), ranges::end(__range), __n)
    { }

    template<__different_from<subrange> _Pair>
      requires __pair_like_convertible_from<_Pair, const _Iter&, const _Sent&>
    _LIBCPP_HIDE_FROM_ABI
    constexpr operator _Pair() const {
      return _Pair(__begin_, __end_);
    }

    _LIBCPP_HIDE_FROM_ABI
    constexpr _Iter begin() const requires copyable<_Iter> {
      return __begin_;
    }

    [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Iter begin() requires (!copyable<_Iter>) {
      return _VSTD::move(__begin_);
    }

    _LIBCPP_HIDE_FROM_ABI
    constexpr _Sent end() const {
      return __end_;
    }

    [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr bool empty() const {
      return __begin_ == __end_;
    }

    _LIBCPP_HIDE_FROM_ABI
    constexpr make_unsigned_t<iter_difference_t<_Iter>> size() const
      requires (_Kind == subrange_kind::sized)
    {
      if constexpr (_StoreSize)
        return __size_;
      else
        return _VSTD::__to_unsigned_like(__end_ - __begin_);
    }

    [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr subrange next(iter_difference_t<_Iter> __n = 1) const&
      requires forward_iterator<_Iter>
    {
      auto __tmp = *this;
      __tmp.advance(__n);
      return __tmp;
    }

    [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr subrange next(iter_difference_t<_Iter> __n = 1) && {
      advance(__n);
      return _VSTD::move(*this);
    }

    [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr subrange prev(iter_difference_t<_Iter> __n = 1) const
      requires bidirectional_iterator<_Iter>
    {
      auto __tmp = *this;
      __tmp.advance(-__n);
      return __tmp;
    }

    _LIBCPP_HIDE_FROM_ABI
    constexpr subrange& advance(iter_difference_t<_Iter> __n) {
      if constexpr (bidirectional_iterator<_Iter>) {
        if (__n < 0) {
          ranges::advance(__begin_, __n);
          if constexpr (_StoreSize)
            __size_ += _VSTD::__to_unsigned_like(-__n);
          return *this;
        }
      }

      auto __d = __n - ranges::advance(__begin_, __n, __end_);
      if constexpr (_StoreSize)
        __size_ -= _VSTD::__to_unsigned_like(__d);
      return *this;
    }
  };

  template<input_or_output_iterator _Iter, sentinel_for<_Iter> _Sent>
  subrange(_Iter, _Sent) -> subrange<_Iter, _Sent>;

  template<input_or_output_iterator _Iter, sentinel_for<_Iter> _Sent>
  subrange(_Iter, _Sent, make_unsigned_t<iter_difference_t<_Iter>>)
    -> subrange<_Iter, _Sent, subrange_kind::sized>;

  template<borrowed_range _Range>
  subrange(_Range&&) -> subrange<iterator_t<_Range>, sentinel_t<_Range>,
                                 (sized_range<_Range> || sized_sentinel_for<sentinel_t<_Range>, iterator_t<_Range>>)
                                   ? subrange_kind::sized : subrange_kind::unsized>;

  template<borrowed_range _Range>
  subrange(_Range&&, make_unsigned_t<range_difference_t<_Range>>)
    -> subrange<iterator_t<_Range>, sentinel_t<_Range>, subrange_kind::sized>;

  template<size_t _Index, class _Iter, class _Sent, subrange_kind _Kind>
    requires (_Index < 2)
  _LIBCPP_HIDE_FROM_ABI
  constexpr auto get(const subrange<_Iter, _Sent, _Kind>& __subrange) {
    if constexpr (_Index == 0)
      return __subrange.begin();
    else
      return __subrange.end();
  }

  template<size_t _Index, class _Iter, class _Sent, subrange_kind _Kind>
    requires (_Index < 2)
  _LIBCPP_HIDE_FROM_ABI
  constexpr auto get(subrange<_Iter, _Sent, _Kind>&& __subrange) {
    if constexpr (_Index == 0)
      return __subrange.begin();
    else
      return __subrange.end();
  }

  template<class _Ip, class _Sp, subrange_kind _Kp>
  inline constexpr bool enable_borrowed_range<subrange<_Ip, _Sp, _Kp>> = true;

  template<range _Rp>
  using borrowed_subrange_t = _If<borrowed_range<_Rp>, subrange<iterator_t<_Rp>>, dangling>;
} // namespace ranges

// [range.subrange.general]

using ranges::get;

// [ranges.syn]

template<class _Ip, class _Sp, ranges::subrange_kind _Kp>
struct tuple_size<ranges::subrange<_Ip, _Sp, _Kp>> : integral_constant<size_t, 2> {};

template<class _Ip, class _Sp, ranges::subrange_kind _Kp>
struct tuple_element<0, ranges::subrange<_Ip, _Sp, _Kp>> {
  using type = _Ip;
};

template<class _Ip, class _Sp, ranges::subrange_kind _Kp>
struct tuple_element<1, ranges::subrange<_Ip, _Sp, _Kp>> {
  using type = _Sp;
};

template<class _Ip, class _Sp, ranges::subrange_kind _Kp>
struct tuple_element<0, const ranges::subrange<_Ip, _Sp, _Kp>> {
  using type = _Ip;
};

template<class _Ip, class _Sp, ranges::subrange_kind _Kp>
struct tuple_element<1, const ranges::subrange<_Ip, _Sp, _Kp>> {
  using type = _Sp;
};

#endif // !defined(_LIBCPP_HAS_NO_RANGES)

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___RANGES_SUBRANGE_H