// -*- 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_FILTER_VIEW_H
#define _LIBCPP___RANGES_FILTER_VIEW_H

#include <__algorithm/ranges_find_if.h>
#include <__concepts/constructible.h>
#include <__concepts/copyable.h>
#include <__concepts/derived_from.h>
#include <__concepts/equality_comparable.h>
#include <__config>
#include <__debug>
#include <__functional/bind_back.h>
#include <__functional/invoke.h>
#include <__functional/reference_wrapper.h>
#include <__iterator/concepts.h>
#include <__iterator/iter_move.h>
#include <__iterator/iter_swap.h>
#include <__iterator/iterator_traits.h>
#include <__memory/addressof.h>
#include <__ranges/access.h>
#include <__ranges/all.h>
#include <__ranges/concepts.h>
#include <__ranges/copyable_box.h>
#include <__ranges/non_propagating_cache.h>
#include <__ranges/range_adaptor.h>
#include <__ranges/view_interface.h>
#include <__utility/forward.h>
#include <__utility/in_place.h>
#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 _LIBCPP_STD_VER > 17

namespace ranges {

  template <input_range _View, indirect_unary_predicate<iterator_t<_View>> _Pred>
    requires view<_View> && is_object_v<_Pred>
  class __filter_view_iterator;

  template <input_range _View, indirect_unary_predicate<iterator_t<_View>> _Pred>
    requires view<_View> && is_object_v<_Pred>
  class __filter_view_sentinel;

  template<input_range _View, indirect_unary_predicate<iterator_t<_View>> _Pred>
    requires view<_View> && is_object_v<_Pred>
  class filter_view : public view_interface<filter_view<_View, _Pred>> {
    _LIBCPP_NO_UNIQUE_ADDRESS _View __base_ = _View();
    _LIBCPP_NO_UNIQUE_ADDRESS __copyable_box<_Pred> __pred_;

    // We cache the result of begin() to allow providing an amortized O(1) begin() whenever
    // the underlying range is at least a forward_range.
    static constexpr bool _UseCache = forward_range<_View>;
    using _Cache = _If<_UseCache, __non_propagating_cache<iterator_t<_View>>, __empty_cache>;
    _LIBCPP_NO_UNIQUE_ADDRESS _Cache __cached_begin_ = _Cache();

    using __iterator = __filter_view_iterator<_View, _Pred>;
    using __sentinel = __filter_view_sentinel<_View, _Pred>;

    friend __iterator;
    friend __sentinel;

  public:
    _LIBCPP_HIDE_FROM_ABI
    filter_view() requires default_initializable<_View> && default_initializable<_Pred> = default;

    _LIBCPP_HIDE_FROM_ABI
    constexpr filter_view(_View __base, _Pred __pred)
      : __base_(std::move(__base)), __pred_(in_place, std::move(__pred))
    { }

    template<class _Vp = _View>
    _LIBCPP_HIDE_FROM_ABI
    constexpr _View base() const& requires copy_constructible<_Vp> { return __base_; }
    _LIBCPP_HIDE_FROM_ABI
    constexpr _View base() && { return std::move(__base_); }

    _LIBCPP_HIDE_FROM_ABI
    constexpr _Pred const& pred() const { return *__pred_; }

    _LIBCPP_HIDE_FROM_ABI
    constexpr __iterator begin() {
      _LIBCPP_ASSERT(__pred_.__has_value(), "Trying to call begin() on a filter_view that does not have a valid predicate.");
      if constexpr (_UseCache) {
        if (!__cached_begin_.__has_value()) {
          __cached_begin_.__emplace(ranges::find_if(__base_, std::ref(*__pred_)));
        }
        return {*this, *__cached_begin_};
      } else {
        return {*this, ranges::find_if(__base_, std::ref(*__pred_))};
      }
    }

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

  template<class _Range, class _Pred>
  filter_view(_Range&&, _Pred) -> filter_view<views::all_t<_Range>, _Pred>;

  template<class _View>
  struct __filter_iterator_category { };

  template<forward_range _View>
  struct __filter_iterator_category<_View> {
    using _Cat = typename iterator_traits<iterator_t<_View>>::iterator_category;
    using iterator_category =
      _If<derived_from<_Cat, bidirectional_iterator_tag>, bidirectional_iterator_tag,
      _If<derived_from<_Cat, forward_iterator_tag>,       forward_iterator_tag,
      /* else */                                          _Cat
    >>;
  };

  template<input_range _View, indirect_unary_predicate<iterator_t<_View>> _Pred>
    requires view<_View> && is_object_v<_Pred>
  class __filter_view_iterator : public __filter_iterator_category<_View> {

    using __filter_view = filter_view<_View, _Pred>;

  public:
    _LIBCPP_NO_UNIQUE_ADDRESS iterator_t<_View> __current_ = iterator_t<_View>();
    _LIBCPP_NO_UNIQUE_ADDRESS __filter_view* __parent_ = nullptr;

    using iterator_concept =
      _If<bidirectional_range<_View>, bidirectional_iterator_tag,
      _If<forward_range<_View>,       forward_iterator_tag,
      /* else */                      input_iterator_tag
    >>;
    // using iterator_category = inherited;
    using value_type = range_value_t<_View>;
    using difference_type = range_difference_t<_View>;

    _LIBCPP_HIDE_FROM_ABI
    __filter_view_iterator() requires default_initializable<iterator_t<_View>> = default;

    _LIBCPP_HIDE_FROM_ABI
    constexpr __filter_view_iterator(__filter_view& __parent, iterator_t<_View> __current)
      : __current_(std::move(__current)), __parent_(std::addressof(__parent))
    { }

    _LIBCPP_HIDE_FROM_ABI
    constexpr iterator_t<_View> const& base() const& noexcept { return __current_; }
    _LIBCPP_HIDE_FROM_ABI
    constexpr iterator_t<_View> base() && { return std::move(__current_); }

    _LIBCPP_HIDE_FROM_ABI
    constexpr range_reference_t<_View> operator*() const { return *__current_; }
    _LIBCPP_HIDE_FROM_ABI
    constexpr iterator_t<_View> operator->() const
      requires __has_arrow<iterator_t<_View>> && copyable<iterator_t<_View>>
    {
      return __current_;
    }

    _LIBCPP_HIDE_FROM_ABI
    constexpr __filter_view_iterator& operator++() {
      __current_ = ranges::find_if(std::move(++__current_), ranges::end(__parent_->__base_),
                                   std::ref(*__parent_->__pred_));
      return *this;
    }
    _LIBCPP_HIDE_FROM_ABI
    constexpr void operator++(int) { ++*this; }
    _LIBCPP_HIDE_FROM_ABI
    constexpr __filter_view_iterator operator++(int) requires forward_range<_View> {
      auto __tmp = *this;
      ++*this;
      return __tmp;
    }

    _LIBCPP_HIDE_FROM_ABI
    constexpr __filter_view_iterator& operator--() requires bidirectional_range<_View> {
      do {
        --__current_;
      } while (!std::invoke(*__parent_->__pred_, *__current_));
      return *this;
    }
    _LIBCPP_HIDE_FROM_ABI
    constexpr __filter_view_iterator operator--(int) requires bidirectional_range<_View> {
      auto tmp = *this;
      --*this;
      return tmp;
    }

    _LIBCPP_HIDE_FROM_ABI
    friend constexpr bool operator==(__filter_view_iterator const& __x, __filter_view_iterator const& __y)
      requires equality_comparable<iterator_t<_View>>
    {
      return __x.__current_ == __y.__current_;
    }

    _LIBCPP_HIDE_FROM_ABI
    friend constexpr range_rvalue_reference_t<_View> iter_move(__filter_view_iterator const& __it)
      noexcept(noexcept(ranges::iter_move(__it.__current_)))
    {
      return ranges::iter_move(__it.__current_);
    }

    _LIBCPP_HIDE_FROM_ABI
    friend constexpr void iter_swap(__filter_view_iterator const& __x, __filter_view_iterator const& __y)
      noexcept(noexcept(ranges::iter_swap(__x.__current_, __y.__current_)))
      requires indirectly_swappable<iterator_t<_View>>
    {
      return ranges::iter_swap(__x.__current_, __y.__current_);
    }
  };

  template<input_range _View, indirect_unary_predicate<iterator_t<_View>> _Pred>
    requires view<_View> && is_object_v<_Pred>
  class __filter_view_sentinel {
    using __filter_view = filter_view<_View, _Pred>;

  public:
    sentinel_t<_View> __end_ = sentinel_t<_View>();

    _LIBCPP_HIDE_FROM_ABI
    __filter_view_sentinel() = default;

    _LIBCPP_HIDE_FROM_ABI
    constexpr explicit __filter_view_sentinel(__filter_view& __parent)
      : __end_(ranges::end(__parent.__base_))
    { }

    _LIBCPP_HIDE_FROM_ABI
    constexpr sentinel_t<_View> base() const { return __end_; }

    _LIBCPP_HIDE_FROM_ABI friend constexpr bool
    operator==(__filter_view_iterator<_View, _Pred> const& __x, __filter_view_sentinel const& __y) {
      return __x.__current_ == __y.__end_;
    }
  };

namespace views {
namespace __filter {
  struct __fn {
    template<class _Range, class _Pred>
    [[nodiscard]] _LIBCPP_HIDE_FROM_ABI
    constexpr auto operator()(_Range&& __range, _Pred&& __pred) const
      noexcept(noexcept(filter_view(std::forward<_Range>(__range), std::forward<_Pred>(__pred))))
      -> decltype(      filter_view(std::forward<_Range>(__range), std::forward<_Pred>(__pred)))
      { return          filter_view(std::forward<_Range>(__range), std::forward<_Pred>(__pred)); }

    template<class _Pred>
      requires constructible_from<decay_t<_Pred>, _Pred>
    [[nodiscard]] _LIBCPP_HIDE_FROM_ABI
    constexpr auto operator()(_Pred&& __pred) const
      noexcept(is_nothrow_constructible_v<decay_t<_Pred>, _Pred>)
    { return __range_adaptor_closure_t(std::__bind_back(*this, std::forward<_Pred>(__pred))); }
  };
} // namespace __filter

inline namespace __cpo {
  inline constexpr auto filter = __filter::__fn{};
} // namespace __cpo
} // namespace views

} // namespace ranges

#endif // _LIBCPP_STD_VER > 17

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___RANGES_FILTER_VIEW_H
