// -*- 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_JOIN_VIEW_H
#define _LIBCPP___RANGES_JOIN_VIEW_H

#include <__config>
#include <__iterator/concepts.h>
#include <__iterator/iterator_traits.h>
#include <__ranges/access.h>
#include <__ranges/all.h>
#include <__ranges/concepts.h>
#include <__ranges/non_propagating_cache.h>
#include <__ranges/ref_view.h>
#include <__ranges/subrange.h>
#include <__ranges/view_interface.h>
#include <__utility/declval.h>
#include <__utility/forward.h>
#include <optional>
#include <type_traits>

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

_LIBCPP_BEGIN_NAMESPACE_STD

#if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)

namespace ranges {
  template<class>
  struct __join_view_iterator_category {};

  template<class _View>
    requires is_reference_v<range_reference_t<_View>> &&
             forward_range<_View> &&
             forward_range<range_reference_t<_View>>
  struct __join_view_iterator_category<_View> {
    using _OuterC = typename iterator_traits<iterator_t<_View>>::iterator_category;
    using _InnerC = typename iterator_traits<iterator_t<range_reference_t<_View>>>::iterator_category;

    using iterator_category = _If<
      derived_from<_OuterC, bidirectional_iterator_tag> && derived_from<_InnerC, bidirectional_iterator_tag>,
      bidirectional_iterator_tag,
      _If<
        derived_from<_OuterC, forward_iterator_tag> && derived_from<_InnerC, forward_iterator_tag>,
        forward_iterator_tag,
        input_iterator_tag
      >
    >;
  };

  template<input_range _View>
    requires view<_View> && input_range<range_reference_t<_View>>
  class join_view
    : public view_interface<join_view<_View>> {
  private:
    using _InnerRange = range_reference_t<_View>;

    template<bool> struct __iterator;
    template<bool> struct __sentinel;

    static constexpr bool _UseCache = !is_reference_v<_InnerRange>;
    using _Cache = _If<_UseCache, __non_propagating_cache<remove_cvref_t<_InnerRange>>, __empty_cache>;
    _LIBCPP_NO_UNIQUE_ADDRESS _Cache __cache_;
    _LIBCPP_NO_UNIQUE_ADDRESS _View __base_ = _View();

  public:
    _LIBCPP_HIDE_FROM_ABI
    join_view() requires default_initializable<_View> = default;

    _LIBCPP_HIDE_FROM_ABI
    constexpr explicit join_view(_View __base)
      : __base_(std::move(__base)) {}

    _LIBCPP_HIDE_FROM_ABI
    constexpr _View base() const& requires copy_constructible<_View> { return __base_; }

    _LIBCPP_HIDE_FROM_ABI
    constexpr _View base() && { return std::move(__base_); }

    _LIBCPP_HIDE_FROM_ABI
    constexpr auto begin() {
      constexpr bool __use_const = __simple_view<_View> &&
                                   is_reference_v<range_reference_t<_View>>;
      return __iterator<__use_const>{*this, ranges::begin(__base_)};
    }

    template<class _V2 = _View>
    _LIBCPP_HIDE_FROM_ABI
    constexpr auto begin() const
      requires input_range<const _V2> &&
               is_reference_v<range_reference_t<const _V2>>
    {
      return __iterator<true>{*this, ranges::begin(__base_)};
    }

    _LIBCPP_HIDE_FROM_ABI
    constexpr auto end() {
      if constexpr (forward_range<_View> &&
                    is_reference_v<_InnerRange> &&
                    forward_range<_InnerRange> &&
                    common_range<_View> &&
                    common_range<_InnerRange>)
        return __iterator<__simple_view<_View>>{*this, ranges::end(__base_)};
      else
        return __sentinel<__simple_view<_View>>{*this};
    }

    template<class _V2 = _View>
    _LIBCPP_HIDE_FROM_ABI
    constexpr auto end() const
      requires input_range<const _V2> &&
               is_reference_v<range_reference_t<const _V2>>
    {
      using _ConstInnerRange = range_reference_t<const _View>;
      if constexpr (forward_range<const _View> &&
                    is_reference_v<_ConstInnerRange> &&
                    forward_range<_ConstInnerRange> &&
                    common_range<const _View> &&
                    common_range<_ConstInnerRange>) {
        return __iterator<true>{*this, ranges::end(__base_)};
      } else {
        return __sentinel<true>{*this};
      }
    }
  };

  template<input_range _View>
    requires view<_View> && input_range<range_reference_t<_View>>
  template<bool _Const> struct join_view<_View>::__sentinel {
    template<bool> friend struct __sentinel;

  private:
    using _Parent = __maybe_const<_Const, join_view>;
    using _Base = __maybe_const<_Const, _View>;
    sentinel_t<_Base> __end_ = sentinel_t<_Base>();

  public:
    _LIBCPP_HIDE_FROM_ABI
    __sentinel() = default;

    _LIBCPP_HIDE_FROM_ABI
    constexpr explicit __sentinel(_Parent& __parent)
      : __end_(ranges::end(__parent.__base_)) {}

    _LIBCPP_HIDE_FROM_ABI
    constexpr __sentinel(__sentinel<!_Const> __s)
      requires _Const && convertible_to<sentinel_t<_View>, sentinel_t<_Base>>
      : __end_(std::move(__s.__end_)) {}

    template<bool _OtherConst>
      requires sentinel_for<sentinel_t<_Base>, iterator_t<__maybe_const<_OtherConst, _View>>>
    _LIBCPP_HIDE_FROM_ABI
    friend constexpr bool operator==(const __iterator<_OtherConst>& __x, const __sentinel& __y) {
      return __x.__outer_ == __y.__end_;
    }
  };

  template<input_range _View>
    requires view<_View> && input_range<range_reference_t<_View>>
  template<bool _Const> struct join_view<_View>::__iterator
    : public __join_view_iterator_category<__maybe_const<_Const, _View>> {

    template<bool> friend struct __iterator;

  private:
    using _Parent = __maybe_const<_Const, join_view>;
    using _Base = __maybe_const<_Const, _View>;
    using _Outer = iterator_t<_Base>;
    using _Inner = iterator_t<range_reference_t<_Base>>;

    static constexpr bool __ref_is_glvalue = is_reference_v<range_reference_t<_Base>>;

  public:
    _Outer __outer_ = _Outer();

  private:
    optional<_Inner> __inner_;
    _Parent *__parent_ = nullptr;

    _LIBCPP_HIDE_FROM_ABI
    constexpr void __satisfy() {
      for (; __outer_ != ranges::end(__parent_->__base_); ++__outer_) {
        auto&& __inner = [&]() -> auto&& {
          if constexpr (__ref_is_glvalue)
            return *__outer_;
          else
            return __parent_->__cache_.__emplace_from([&]() -> decltype(auto) { return *__outer_; });
        }();
        __inner_ = ranges::begin(__inner);
        if (*__inner_ != ranges::end(__inner))
          return;
      }

      if constexpr (__ref_is_glvalue)
        __inner_.reset();
    }

  public:
    using iterator_concept = _If<
      __ref_is_glvalue && bidirectional_range<_Base> && bidirectional_range<range_reference_t<_Base>>,
      bidirectional_iterator_tag,
      _If<
        __ref_is_glvalue && forward_range<_Base> && forward_range<range_reference_t<_Base>>,
        forward_iterator_tag,
        input_iterator_tag
      >
    >;

    using value_type = range_value_t<range_reference_t<_Base>>;

    using difference_type = common_type_t<
      range_difference_t<_Base>, range_difference_t<range_reference_t<_Base>>>;

    _LIBCPP_HIDE_FROM_ABI
    __iterator() requires default_initializable<_Outer> = default;

    _LIBCPP_HIDE_FROM_ABI
    constexpr __iterator(_Parent& __parent, _Outer __outer)
      : __outer_(std::move(__outer))
      , __parent_(std::addressof(__parent)) {
      __satisfy();
    }

    _LIBCPP_HIDE_FROM_ABI
    constexpr __iterator(__iterator<!_Const> __i)
      requires _Const &&
               convertible_to<iterator_t<_View>, _Outer> &&
               convertible_to<iterator_t<_InnerRange>, _Inner>
      : __outer_(std::move(__i.__outer_))
      , __inner_(std::move(__i.__inner_))
      , __parent_(__i.__parent_) {}

    _LIBCPP_HIDE_FROM_ABI
    constexpr decltype(auto) operator*() const {
      return **__inner_;
    }

    _LIBCPP_HIDE_FROM_ABI
    constexpr _Inner operator->() const
      requires __has_arrow<_Inner> && copyable<_Inner>
    {
      return *__inner_;
    }

    _LIBCPP_HIDE_FROM_ABI
    constexpr __iterator& operator++() {
      auto&& __inner = [&]() -> auto&& {
        if constexpr (__ref_is_glvalue)
          return *__outer_;
        else
          return *__parent_->__cache_;
      }();
      if (++*__inner_ == ranges::end(__inner)) {
        ++__outer_;
        __satisfy();
      }
      return *this;
    }

    _LIBCPP_HIDE_FROM_ABI
    constexpr void operator++(int) {
      ++*this;
    }

    _LIBCPP_HIDE_FROM_ABI
    constexpr __iterator operator++(int)
      requires __ref_is_glvalue &&
               forward_range<_Base> &&
               forward_range<range_reference_t<_Base>>
    {
      auto __tmp = *this;
      ++*this;
      return __tmp;
    }

    _LIBCPP_HIDE_FROM_ABI
    constexpr __iterator& operator--()
      requires __ref_is_glvalue &&
               bidirectional_range<_Base> &&
               bidirectional_range<range_reference_t<_Base>> &&
               common_range<range_reference_t<_Base>>
    {
      if (__outer_ == ranges::end(__parent_->__base_))
        __inner_ = ranges::end(*--__outer_);

      // Skip empty inner ranges when going backwards.
      while (*__inner_ == ranges::begin(*__outer_)) {
        __inner_ = ranges::end(*--__outer_);
      }

      --*__inner_;
      return *this;
    }

    _LIBCPP_HIDE_FROM_ABI
    constexpr __iterator operator--(int)
      requires __ref_is_glvalue &&
               bidirectional_range<_Base> &&
               bidirectional_range<range_reference_t<_Base>> &&
               common_range<range_reference_t<_Base>>
    {
      auto __tmp = *this;
      --*this;
      return __tmp;
    }

    _LIBCPP_HIDE_FROM_ABI
    friend constexpr bool operator==(const __iterator& __x, const __iterator& __y)
      requires __ref_is_glvalue &&
               equality_comparable<iterator_t<_Base>> &&
               equality_comparable<iterator_t<range_reference_t<_Base>>>
    {
      return __x.__outer_ == __y.__outer_ && __x.__inner_ == __y.__inner_;
    }

    _LIBCPP_HIDE_FROM_ABI
    friend constexpr decltype(auto) iter_move(const __iterator& __i)
      noexcept(noexcept(ranges::iter_move(*__i.__inner_)))
    {
      return ranges::iter_move(*__i.__inner_);
    }

    _LIBCPP_HIDE_FROM_ABI
    friend constexpr void iter_swap(const __iterator& __x, const __iterator& __y)
      noexcept(noexcept(ranges::iter_swap(*__x.__inner_, *__y.__inner_)))
      requires indirectly_swappable<_Inner>
    {
      return ranges::iter_swap(*__x.__inner_, *__y.__inner_);
    }
  };

  template<class _Range>
  explicit join_view(_Range&&) -> join_view<views::all_t<_Range>>;

} // namespace ranges

#endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___RANGES_JOIN_VIEW_H