//===----------------------------------------------------------------------===//
//
// 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 SUPPORT_TEST_ITERATORS_H
#define SUPPORT_TEST_ITERATORS_H

#include <cassert>
#include <iterator>
#include <stdexcept>
#include <utility>

#include "test_macros.h"

template <class It>
class output_iterator
{
    It it_;

    template <class U> friend class output_iterator;
public:
    typedef          std::output_iterator_tag                  iterator_category;
    typedef void                                               value_type;
    typedef typename std::iterator_traits<It>::difference_type difference_type;
    typedef It                                                 pointer;
    typedef typename std::iterator_traits<It>::reference       reference;

    TEST_CONSTEXPR_CXX14 It base() const {return it_;}

    TEST_CONSTEXPR_CXX14 output_iterator() {}
    explicit TEST_CONSTEXPR_CXX14 output_iterator(It it) : it_(it) {}
    template <class U>
        TEST_CONSTEXPR_CXX14 output_iterator(const output_iterator<U>& u) :it_(u.it_) {}

    TEST_CONSTEXPR_CXX14 reference operator*() const {return *it_;}

    TEST_CONSTEXPR_CXX14 output_iterator& operator++() {++it_; return *this;}
    TEST_CONSTEXPR_CXX14 output_iterator operator++(int)
        {output_iterator tmp(*this); ++(*this); return tmp;}

    template <class T>
    void operator,(T const &) = delete;
};

// This is the Cpp17InputIterator requirement as described in Table 87 ([input.iterators]),
// formerly known as InputIterator prior to C++20.
template <class It, class ItTraits = It>
class cpp17_input_iterator
{
    typedef std::iterator_traits<ItTraits> Traits;
    It it_;

    template <class U, class T> friend class cpp17_input_iterator;
public:
    typedef          std::input_iterator_tag                   iterator_category;
    typedef typename Traits::value_type                        value_type;
    typedef typename Traits::difference_type                   difference_type;
    typedef It                                                 pointer;
    typedef typename Traits::reference                         reference;

    TEST_CONSTEXPR_CXX14 It base() const {return it_;}

    TEST_CONSTEXPR_CXX14 cpp17_input_iterator() : it_() {}
    explicit TEST_CONSTEXPR_CXX14 cpp17_input_iterator(It it) : it_(it) {}
    template <class U, class T>
        TEST_CONSTEXPR_CXX14 cpp17_input_iterator(const cpp17_input_iterator<U, T>& u) :it_(u.it_) {}

    TEST_CONSTEXPR_CXX14 reference operator*() const {return *it_;}
    TEST_CONSTEXPR_CXX14 pointer operator->() const {return it_;}

    TEST_CONSTEXPR_CXX14 cpp17_input_iterator& operator++() {++it_; return *this;}
    TEST_CONSTEXPR_CXX14 cpp17_input_iterator operator++(int)
        {cpp17_input_iterator tmp(*this); ++(*this); return tmp;}

    friend TEST_CONSTEXPR_CXX14 bool operator==(const cpp17_input_iterator& x, const cpp17_input_iterator& y)
        {return x.it_ == y.it_;}
    friend TEST_CONSTEXPR_CXX14 bool operator!=(const cpp17_input_iterator& x, const cpp17_input_iterator& y)
        {return !(x == y);}

    template <class T>
    void operator,(T const &) = delete;
};

template <class T, class TV, class U, class UV>
bool operator==(const cpp17_input_iterator<T, TV>& x, const cpp17_input_iterator<U, UV>& y)
{
    return x.base() == y.base();
}

template <class T, class TV, class U, class UV>
bool operator!=(const cpp17_input_iterator<T, TV>& x, const cpp17_input_iterator<U, UV>& y)
{
    return !(x == y);
}

template <class It>
class forward_iterator
{
    It it_;

    template <class U> friend class forward_iterator;
public:
    typedef          std::forward_iterator_tag                 iterator_category;
    typedef typename std::iterator_traits<It>::value_type      value_type;
    typedef typename std::iterator_traits<It>::difference_type difference_type;
    typedef It                                                 pointer;
    typedef typename std::iterator_traits<It>::reference       reference;

    TEST_CONSTEXPR_CXX14 It base() const {return it_;}

    TEST_CONSTEXPR_CXX14 forward_iterator() : it_() {}
    explicit TEST_CONSTEXPR_CXX14 forward_iterator(It it) : it_(it) {}
    template <class U>
        TEST_CONSTEXPR_CXX14 forward_iterator(const forward_iterator<U>& u) :it_(u.it_) {}

    TEST_CONSTEXPR_CXX14 reference operator*() const {return *it_;}
    TEST_CONSTEXPR_CXX14 pointer operator->() const {return it_;}

    TEST_CONSTEXPR_CXX14 forward_iterator& operator++() {++it_; return *this;}
    TEST_CONSTEXPR_CXX14 forward_iterator operator++(int)
        {forward_iterator tmp(*this); ++(*this); return tmp;}

    friend TEST_CONSTEXPR_CXX14 bool operator==(const forward_iterator& x, const forward_iterator& y)
        {return x.it_ == y.it_;}
    friend TEST_CONSTEXPR_CXX14 bool operator!=(const forward_iterator& x, const forward_iterator& y)
        {return !(x == y);}

    template <class T>
    void operator,(T const &) = delete;
};

template <class T, class U>
TEST_CONSTEXPR_CXX14
bool operator==(const forward_iterator<T>& x, const forward_iterator<U>& y)
{
    return x.base() == y.base();
}

template <class T, class U>
TEST_CONSTEXPR_CXX14
bool operator!=(const forward_iterator<T>& x, const forward_iterator<U>& y)
{
    return !(x == y);
}

template <class It>
class non_default_constructible_iterator
{
    It it_;

    template <class U> friend class non_default_constructible_iterator;
public:
    typedef          std::input_iterator_tag                   iterator_category;
    typedef typename std::iterator_traits<It>::value_type      value_type;
    typedef typename std::iterator_traits<It>::difference_type difference_type;
    typedef It                                                 pointer;
    typedef typename std::iterator_traits<It>::reference       reference;

    TEST_CONSTEXPR_CXX14 It base() const {return it_;}

    non_default_constructible_iterator() = delete;

    explicit TEST_CONSTEXPR_CXX14 non_default_constructible_iterator(It it) : it_(it) {}
    template <class U>
        TEST_CONSTEXPR_CXX14 non_default_constructible_iterator(const non_default_constructible_iterator<U>& u) :it_(u.it_) {}

    TEST_CONSTEXPR_CXX14 reference operator*() const {return *it_;}
    TEST_CONSTEXPR_CXX14 pointer operator->() const {return it_;}

    TEST_CONSTEXPR_CXX14 non_default_constructible_iterator& operator++() {++it_; return *this;}
    TEST_CONSTEXPR_CXX14 non_default_constructible_iterator operator++(int)
        {non_default_constructible_iterator tmp(*this); ++(*this); return tmp;}

    friend TEST_CONSTEXPR_CXX14 bool operator==(const non_default_constructible_iterator& x, const non_default_constructible_iterator& y)
        {return x.it_ == y.it_;}
    friend TEST_CONSTEXPR_CXX14 bool operator!=(const non_default_constructible_iterator& x, const non_default_constructible_iterator& y)
        {return !(x == y);}

    template <class T>
    void operator,(T const &) = delete;
};

template <class T, class U>
TEST_CONSTEXPR_CXX14
bool operator==(const non_default_constructible_iterator<T>& x, const non_default_constructible_iterator<U>& y)
{
    return x.base() == y.base();
}

template <class T, class U>
TEST_CONSTEXPR_CXX14
bool operator!=(const non_default_constructible_iterator<T>& x, const non_default_constructible_iterator<U>& y)
{
    return !(x == y);
}

template <class It>
class bidirectional_iterator
{
    It it_;

    template <class U> friend class bidirectional_iterator;
public:
    typedef          std::bidirectional_iterator_tag           iterator_category;
    typedef typename std::iterator_traits<It>::value_type      value_type;
    typedef typename std::iterator_traits<It>::difference_type difference_type;
    typedef It                                                 pointer;
    typedef typename std::iterator_traits<It>::reference       reference;

    TEST_CONSTEXPR_CXX14 It base() const {return it_;}

    TEST_CONSTEXPR_CXX14 bidirectional_iterator() : it_() {}
    explicit TEST_CONSTEXPR_CXX14 bidirectional_iterator(It it) : it_(it) {}
    template <class U>
        TEST_CONSTEXPR_CXX14 bidirectional_iterator(const bidirectional_iterator<U>& u) :it_(u.it_) {}

    TEST_CONSTEXPR_CXX14 reference operator*() const {return *it_;}
    TEST_CONSTEXPR_CXX14 pointer operator->() const {return it_;}

    TEST_CONSTEXPR_CXX14 bidirectional_iterator& operator++() {++it_; return *this;}
    TEST_CONSTEXPR_CXX14 bidirectional_iterator operator++(int)
        {bidirectional_iterator tmp(*this); ++(*this); return tmp;}

    TEST_CONSTEXPR_CXX14 bidirectional_iterator& operator--() {--it_; return *this;}
    TEST_CONSTEXPR_CXX14 bidirectional_iterator operator--(int)
        {bidirectional_iterator tmp(*this); --(*this); return tmp;}

    template <class T>
    void operator,(T const &) = delete;
};

template <class T, class U>
TEST_CONSTEXPR_CXX14
bool operator==(const bidirectional_iterator<T>& x, const bidirectional_iterator<U>& y)
{
    return x.base() == y.base();
}

template <class T, class U>
TEST_CONSTEXPR_CXX14
bool operator!=(const bidirectional_iterator<T>& x, const bidirectional_iterator<U>& y)
{
    return !(x == y);
}

template <class It>
class random_access_iterator
{
    It it_;

    template <class U> friend class random_access_iterator;
public:
    typedef          std::random_access_iterator_tag           iterator_category;
    typedef typename std::iterator_traits<It>::value_type      value_type;
    typedef typename std::iterator_traits<It>::difference_type difference_type;
    typedef It                                                 pointer;
    typedef typename std::iterator_traits<It>::reference       reference;

    TEST_CONSTEXPR_CXX14 It base() const {return it_;}

    TEST_CONSTEXPR_CXX14 random_access_iterator() : it_() {}
    explicit TEST_CONSTEXPR_CXX14 random_access_iterator(It it) : it_(it) {}
    template <class U>
        TEST_CONSTEXPR_CXX14 random_access_iterator(const random_access_iterator<U>& u) :it_(u.it_) {}

    TEST_CONSTEXPR_CXX14 reference operator*() const {return *it_;}
    TEST_CONSTEXPR_CXX14 pointer operator->() const {return it_;}

    TEST_CONSTEXPR_CXX14 random_access_iterator& operator++() {++it_; return *this;}
    TEST_CONSTEXPR_CXX14 random_access_iterator operator++(int)
        {random_access_iterator tmp(*this); ++(*this); return tmp;}

    TEST_CONSTEXPR_CXX14 random_access_iterator& operator--() {--it_; return *this;}
    TEST_CONSTEXPR_CXX14 random_access_iterator operator--(int)
        {random_access_iterator tmp(*this); --(*this); return tmp;}

    TEST_CONSTEXPR_CXX14 random_access_iterator& operator+=(difference_type n) {it_ += n; return *this;}
    TEST_CONSTEXPR_CXX14 random_access_iterator operator+(difference_type n) const
        {random_access_iterator tmp(*this); tmp += n; return tmp;}
    friend TEST_CONSTEXPR_CXX14 random_access_iterator operator+(difference_type n, random_access_iterator x)
        {x += n; return x;}
    TEST_CONSTEXPR_CXX14 random_access_iterator& operator-=(difference_type n) {return *this += -n;}
    TEST_CONSTEXPR_CXX14 random_access_iterator operator-(difference_type n) const
        {random_access_iterator tmp(*this); tmp -= n; return tmp;}

    TEST_CONSTEXPR_CXX14 reference operator[](difference_type n) const {return it_[n];}

    template <class T>
    void operator,(T const &) = delete;
};

template <class T, class U>
TEST_CONSTEXPR_CXX14
bool operator==(const random_access_iterator<T>& x, const random_access_iterator<U>& y)
{
    return x.base() == y.base();
}

template <class T, class U>
TEST_CONSTEXPR_CXX14
bool operator!=(const random_access_iterator<T>& x, const random_access_iterator<U>& y)
{
    return !(x == y);
}

template <class T, class U>
TEST_CONSTEXPR_CXX14
bool operator<(const random_access_iterator<T>& x, const random_access_iterator<U>& y)
{
    return x.base() < y.base();
}

template <class T, class U>
TEST_CONSTEXPR_CXX14
bool operator<=(const random_access_iterator<T>& x, const random_access_iterator<U>& y)
{
    return !(y < x);
}

template <class T, class U>
TEST_CONSTEXPR_CXX14
bool operator>(const random_access_iterator<T>& x, const random_access_iterator<U>& y)
{
    return y < x;
}

template <class T, class U>
TEST_CONSTEXPR_CXX14
bool operator>=(const random_access_iterator<T>& x, const random_access_iterator<U>& y)
{
    return !(x < y);
}

template <class T, class U>
TEST_CONSTEXPR_CXX14
typename std::iterator_traits<T>::difference_type
operator-(const random_access_iterator<T>& x, const random_access_iterator<U>& y)
{
    return x.base() - y.base();
}

#if TEST_STD_VER > 17
template <class It>
class contiguous_iterator
{
    static_assert(std::is_pointer_v<It>, "Things probably break in this case");

    It it_;

    template <class U> friend class contiguous_iterator;
public:
    typedef          std::contiguous_iterator_tag              iterator_category;
    typedef typename std::iterator_traits<It>::value_type      value_type;
    typedef typename std::iterator_traits<It>::difference_type difference_type;
    typedef It                                                 pointer;
    typedef typename std::iterator_traits<It>::reference       reference;
    typedef typename std::remove_pointer<It>::type             element_type;

    TEST_CONSTEXPR_CXX14 It base() const {return it_;}

    TEST_CONSTEXPR_CXX14 contiguous_iterator() : it_() {}
    explicit TEST_CONSTEXPR_CXX14 contiguous_iterator(It it) : it_(it) {}
    template <class U>
        TEST_CONSTEXPR_CXX14 contiguous_iterator(const contiguous_iterator<U>& u) : it_(u.it_) {}

    TEST_CONSTEXPR_CXX14 reference operator*() const {return *it_;}
    TEST_CONSTEXPR_CXX14 pointer operator->() const {return it_;}

    TEST_CONSTEXPR_CXX14 contiguous_iterator& operator++() {++it_; return *this;}
    TEST_CONSTEXPR_CXX14 contiguous_iterator operator++(int)
        {contiguous_iterator tmp(*this); ++(*this); return tmp;}

    TEST_CONSTEXPR_CXX14 contiguous_iterator& operator--() {--it_; return *this;}
    TEST_CONSTEXPR_CXX14 contiguous_iterator operator--(int)
        {contiguous_iterator tmp(*this); --(*this); return tmp;}

    TEST_CONSTEXPR_CXX14 contiguous_iterator& operator+=(difference_type n) {it_ += n; return *this;}
    TEST_CONSTEXPR_CXX14 contiguous_iterator operator+(difference_type n) const
        {contiguous_iterator tmp(*this); tmp += n; return tmp;}
    friend TEST_CONSTEXPR_CXX14 contiguous_iterator operator+(difference_type n, contiguous_iterator x)
        {x += n; return x;}
    TEST_CONSTEXPR_CXX14 contiguous_iterator& operator-=(difference_type n) {return *this += -n;}
    TEST_CONSTEXPR_CXX14 contiguous_iterator operator-(difference_type n) const
        {contiguous_iterator tmp(*this); tmp -= n; return tmp;}

    TEST_CONSTEXPR_CXX14 reference operator[](difference_type n) const {return it_[n];}

    friend TEST_CONSTEXPR_CXX14
    difference_type operator-(const contiguous_iterator& x, const contiguous_iterator& y) {
        return x.base() - y.base();
    }

    friend TEST_CONSTEXPR_CXX14
    difference_type operator<(const contiguous_iterator& x, const contiguous_iterator& y) {
        return x.base() < y.base();
    }
    friend TEST_CONSTEXPR_CXX14
    difference_type operator>(const contiguous_iterator& x, const contiguous_iterator& y) {
        return x.base() > y.base();
    }
    friend TEST_CONSTEXPR_CXX14
    difference_type operator<=(const contiguous_iterator& x, const contiguous_iterator& y) {
        return x.base() <= y.base();
    }
    friend TEST_CONSTEXPR_CXX14
    difference_type operator>=(const contiguous_iterator& x, const contiguous_iterator& y) {
        return x.base() >= y.base();
    }
    friend TEST_CONSTEXPR_CXX14
    difference_type operator==(const contiguous_iterator& x, const contiguous_iterator& y) {
        return x.base() == y.base();
    }
    friend TEST_CONSTEXPR_CXX14
    difference_type operator!=(const contiguous_iterator& x, const contiguous_iterator& y) {
        return x.base() != y.base();
    }

    template <class T>
    void operator,(T const &) = delete;
};
#endif

template <class Iter>
TEST_CONSTEXPR_CXX14 Iter base(output_iterator<Iter> i) { return i.base(); }

template <class Iter>
TEST_CONSTEXPR_CXX14 Iter base(cpp17_input_iterator<Iter> i) { return i.base(); }

template <class Iter>
TEST_CONSTEXPR_CXX14 Iter base(forward_iterator<Iter> i) { return i.base(); }

template <class Iter>
TEST_CONSTEXPR_CXX14 Iter base(bidirectional_iterator<Iter> i) { return i.base(); }

template <class Iter>
TEST_CONSTEXPR_CXX14 Iter base(random_access_iterator<Iter> i) { return i.base(); }

#if TEST_STD_VER > 17
template <class Iter>
TEST_CONSTEXPR_CXX14 Iter base(contiguous_iterator<Iter> i) { return i.base(); }
#endif

template <class Iter>    // everything else
TEST_CONSTEXPR_CXX14 Iter base(Iter i) { return i; }

template <typename T>
struct ThrowingIterator {
    typedef std::bidirectional_iterator_tag iterator_category;
    typedef ptrdiff_t                       difference_type;
    typedef const T                         value_type;
    typedef const T *                       pointer;
    typedef const T &                       reference;

    enum ThrowingAction { TAIncrement, TADecrement, TADereference, TAAssignment, TAComparison };

    ThrowingIterator()
        : begin_(nullptr), end_(nullptr), current_(nullptr), action_(TADereference), index_(0) {}
    explicit ThrowingIterator(const T *first, const T *last, int index = 0, ThrowingAction action = TADereference)
        : begin_(first), end_(last), current_(first), action_(action), index_(index) {}
    ThrowingIterator(const ThrowingIterator &rhs)
        : begin_(rhs.begin_), end_(rhs.end_), current_(rhs.current_), action_(rhs.action_), index_(rhs.index_) {}

    ThrowingIterator& operator=(const ThrowingIterator& rhs) {
        if (action_ == TAAssignment && --index_ < 0) {
#ifndef TEST_HAS_NO_EXCEPTIONS
            throw std::runtime_error("throw from iterator assignment");
#else
            assert(false);
#endif
        }
        begin_ = rhs.begin_;
        end_ = rhs.end_;
        current_ = rhs.current_;
        action_ = rhs.action_;
        index_ = rhs.index_;
        return *this;
    }

    reference operator*() const {
        if (action_ == TADereference && --index_ < 0) {
#ifndef TEST_HAS_NO_EXCEPTIONS
            throw std::runtime_error("throw from iterator dereference");
#else
            assert(false);
#endif
        }
        return *current_;
    }

    ThrowingIterator& operator++() {
        if (action_ == TAIncrement && --index_ < 0) {
#ifndef TEST_HAS_NO_EXCEPTIONS
            throw std::runtime_error("throw from iterator increment");
#else
            assert(false);
#endif
        }
        ++current_;
        return *this;
    }

    ThrowingIterator operator++(int) {
        ThrowingIterator temp = *this;
        ++(*this);
        return temp;
    }

    ThrowingIterator& operator--() {
        if (action_ == TADecrement && --index_ < 0) {
#ifndef TEST_HAS_NO_EXCEPTIONS
            throw std::runtime_error("throw from iterator decrement");
#else
            assert(false);
#endif
        }
        --current_;
        return *this;
    }

    ThrowingIterator operator--(int) {
        ThrowingIterator temp = *this;
        --(*this);
        return temp;
    }

    friend bool operator==(const ThrowingIterator& a, const ThrowingIterator& b) {
        if (a.action_ == TAComparison && --a.index_ < 0) {
#ifndef TEST_HAS_NO_EXCEPTIONS
            throw std::runtime_error("throw from iterator comparison");
#else
            assert(false);
#endif
        }
        bool atEndL = a.current_ == a.end_;
        bool atEndR = b.current_ == b.end_;
        if (atEndL != atEndR) return false;  // one is at the end (or empty), the other is not.
        if (atEndL) return true;             // both are at the end (or empty)
        return a.current_ == b.current_;
    }

    friend bool operator!=(const ThrowingIterator& a, const ThrowingIterator& b) {
        return !(a == b);
    }

    template <class T2>
    void operator,(T2 const &) = delete;

private:
    const T* begin_;
    const T* end_;
    const T* current_;
    ThrowingAction action_;
    mutable int index_;
};

template <typename T>
struct NonThrowingIterator {
    typedef std::bidirectional_iterator_tag iterator_category;
    typedef ptrdiff_t                       difference_type;
    typedef const T                         value_type;
    typedef const T *                       pointer;
    typedef const T &                       reference;

    NonThrowingIterator()
        : begin_(nullptr), end_(nullptr), current_(nullptr) {}
    explicit NonThrowingIterator(const T *first, const T *last)
        : begin_(first), end_(last), current_(first) {}
    NonThrowingIterator(const NonThrowingIterator& rhs)
        : begin_(rhs.begin_), end_(rhs.end_), current_(rhs.current_) {}

    NonThrowingIterator& operator=(const NonThrowingIterator& rhs) TEST_NOEXCEPT {
        begin_ = rhs.begin_;
        end_ = rhs.end_;
        current_ = rhs.current_;
        return *this;
    }

    reference operator*() const TEST_NOEXCEPT {
        return *current_;
    }

    NonThrowingIterator& operator++() TEST_NOEXCEPT {
        ++current_;
        return *this;
    }

    NonThrowingIterator operator++(int) TEST_NOEXCEPT {
        NonThrowingIterator temp = *this;
        ++(*this);
        return temp;
    }

    NonThrowingIterator & operator--() TEST_NOEXCEPT {
        --current_;
        return *this;
    }

    NonThrowingIterator operator--(int) TEST_NOEXCEPT {
        NonThrowingIterator temp = *this;
        --(*this);
        return temp;
    }

    friend bool operator==(const NonThrowingIterator& a, const NonThrowingIterator& b) TEST_NOEXCEPT {
        bool atEndL = a.current_ == a.end_;
        bool atEndR = b.current_ == b.end_;
        if (atEndL != atEndR) return false;  // one is at the end (or empty), the other is not.
        if (atEndL) return true;             // both are at the end (or empty)
        return a.current_ == b.current_;
    }

    friend bool operator!=(const NonThrowingIterator& a, const NonThrowingIterator& b) TEST_NOEXCEPT {
        return !(a == b);
    }

    template <class T2>
    void operator,(T2 const &) = delete;

private:
    const T *begin_;
    const T *end_;
    const T *current_;
};

#ifdef TEST_SUPPORTS_RANGES

template <class I>
struct cpp20_input_iterator {
    using value_type = std::iter_value_t<I>;
    using difference_type = std::iter_difference_t<I>;
    using iterator_concept = std::input_iterator_tag;

    cpp20_input_iterator() = delete;

    cpp20_input_iterator(cpp20_input_iterator&&) = default;
    cpp20_input_iterator& operator=(cpp20_input_iterator&&) = default;

    cpp20_input_iterator(cpp20_input_iterator const&) = delete;
    cpp20_input_iterator& operator=(cpp20_input_iterator const&) = delete;

    explicit constexpr cpp20_input_iterator(I base) : base_(std::move(base)) {}

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

    constexpr cpp20_input_iterator& operator++() {
        ++base_;
        return *this;
    }

    constexpr void operator++(int) { ++base_; }

    constexpr const I& base() const& { return base_; }

    constexpr I base() && { return std::move(base_); }

    template <class T>
    void operator,(T const &) = delete;

private:
    I base_ = I();
};

template <std::input_or_output_iterator I>
struct iterator_concept {
    using type = std::output_iterator_tag;
};

template <std::input_iterator I>
struct iterator_concept<I> {
    using type = std::input_iterator_tag;
};

template <std::forward_iterator I>
struct iterator_concept<I> {
    using type = std::forward_iterator_tag;
};

template <std::bidirectional_iterator I>
struct iterator_concept<I> {
    using type = std::bidirectional_iterator_tag;
};

template <std::random_access_iterator I>
struct iterator_concept<I> {
    using type = std::random_access_iterator_tag;
};

template<std::contiguous_iterator I>
struct iterator_concept<I> {
    using type = std::contiguous_iterator_tag;
};

template <std::input_or_output_iterator I>
using iterator_concept_t = typename iterator_concept<I>::type;

template<std::input_or_output_iterator>
struct iter_value_or_void { using type = void; };

template<std::input_iterator I>
struct iter_value_or_void<I> {
    using type = std::iter_value_t<I>;
};

// Iterator adaptor that counts the number of times the iterator has had a successor/predecessor
// operation called. Has two recorders:
// * `stride_count`, which records the total number of calls to an op++, op--, op+=, or op-=.
// * `stride_displacement`, which records the displacement of the calls. This means that both
//   op++/op+= will increase the displacement counter by 1, and op--/op-= will decrease the
//   displacement counter by 1.
template <std::input_or_output_iterator I>
class stride_counting_iterator {
public:
    using value_type = typename iter_value_or_void<I>::type;
    using difference_type = std::iter_difference_t<I>;
    using iterator_concept = iterator_concept_t<I>;

    stride_counting_iterator() = default;

    constexpr explicit stride_counting_iterator(I current) : base_(std::move(current)) {}

    constexpr const I& base() const& { return base_; }

    constexpr I base() && { return std::move(base_); }

    constexpr difference_type stride_count() const { return stride_count_; }

    constexpr difference_type stride_displacement() const { return stride_displacement_; }

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

    constexpr decltype(auto) operator[](difference_type const n) const { return base_[n]; }

    constexpr stride_counting_iterator& operator++() {
        ++base_;
        ++stride_count_;
        ++stride_displacement_;
        return *this;
    }

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

    constexpr stride_counting_iterator operator++(int)
        requires std::forward_iterator<I>
    {
        auto temp = *this;
        ++*this;
        return temp;
    }

    constexpr stride_counting_iterator& operator--()
        requires std::bidirectional_iterator<I>
    {
        --base_;
        ++stride_count_;
        --stride_displacement_;
        return *this;
    }

    constexpr stride_counting_iterator operator--(int)
        requires std::bidirectional_iterator<I>
    {
        auto temp = *this;
        --*this;
        return temp;
    }

    constexpr stride_counting_iterator& operator+=(difference_type const n)
        requires std::random_access_iterator<I>
    {
        base_ += n;
        ++stride_count_;
        ++stride_displacement_;
        return *this;
    }

    constexpr stride_counting_iterator& operator-=(difference_type const n)
        requires std::random_access_iterator<I>
    {
        base_ -= n;
        ++stride_count_;
        --stride_displacement_;
        return *this;
    }

    friend constexpr stride_counting_iterator operator+(stride_counting_iterator i, difference_type const n)
        requires std::random_access_iterator<I>
    {
        return i += n;
    }

    friend constexpr stride_counting_iterator operator+(difference_type const n, stride_counting_iterator i)
        requires std::random_access_iterator<I>
    {
        return i += n;
    }

    friend constexpr stride_counting_iterator operator-(stride_counting_iterator i, difference_type const n)
        requires std::random_access_iterator<I>
    {
        return i -= n;
    }

    friend constexpr difference_type operator-(stride_counting_iterator const& x, stride_counting_iterator const& y)
        requires std::sized_sentinel_for<I, I>
    {
        return x.base() - y.base();
    }

    constexpr bool operator==(stride_counting_iterator const& other) const
        requires std::sentinel_for<I, I>
    {
        return base_ == other.base_;
    }

    template <std::sentinel_for<I> S>
    constexpr bool operator==(S const last) const
    {
        return base_ == last;
    }

    friend constexpr bool operator<(stride_counting_iterator const& x, stride_counting_iterator const& y)
        requires std::random_access_iterator<I>
    {
        return x.base_ < y.base_;
    }

    friend constexpr bool operator>(stride_counting_iterator const& x, stride_counting_iterator const& y)
        requires std::random_access_iterator<I>
    {
        return y < x;
    }

    friend constexpr bool operator<=(stride_counting_iterator const& x, stride_counting_iterator const& y)
        requires std::random_access_iterator<I>
    {
        return !(y < x);
    }

    friend constexpr bool operator>=(stride_counting_iterator const& x, stride_counting_iterator const& y)
        requires std::random_access_iterator<I>
    {
        return !(x < y);
    }

    template <class T>
    void operator,(T const &) = delete;

private:
    I base_;
    difference_type stride_count_ = 0;
    difference_type stride_displacement_ = 0;
};

template<class T, class U>
concept sentinel_for_base = requires(U const& u) {
    u.base();
    requires std::input_or_output_iterator<std::remove_cvref_t<decltype(u.base())>>;
    requires std::equality_comparable_with<T, decltype(u.base())>;
};

template <std::input_or_output_iterator I>
class sentinel_wrapper {
public:
    sentinel_wrapper() = default;
    constexpr explicit sentinel_wrapper(I base) : base_(std::move(base)) {}

    constexpr bool operator==(const I& other) const requires std::equality_comparable<I> {
        return base_ == other;
    }

    constexpr const I& base() const& { return base_; }
    constexpr I base() && { return std::move(base_); }

    template<std::input_or_output_iterator I2>
        requires sentinel_for_base<I, I2>
    constexpr bool operator==(const I2& other) const {
        return base_ == other.base();
    }

private:
    I base_ = I();
};

template <std::input_or_output_iterator I>
class sized_sentinel {
public:
    sized_sentinel() = default;
    constexpr explicit sized_sentinel(I base) : base_(std::move(base)) {}

    constexpr bool operator==(const I& other) const requires std::equality_comparable<I> {
        return base_ == other;
    }

    constexpr const I& base() const& { return base_; }
    constexpr I base() && { return std::move(base_); }

    template<std::input_or_output_iterator I2>
        requires sentinel_for_base<I, I2>
    constexpr bool operator==(const I2& other) const {
        return base_ == other.base();
    }

private:
    I base_ = I();
};

template <std::input_or_output_iterator I>
constexpr auto operator-(sized_sentinel<I> sent, std::input_or_output_iterator auto iter) {
  return sent.base() - iter;
}

template <std::input_or_output_iterator I>
constexpr auto operator-(std::input_or_output_iterator auto iter, sized_sentinel<I> sent) {
  return iter - sent.base();
}

template <class It>
class three_way_contiguous_iterator
{
    static_assert(std::is_pointer_v<It>, "Things probably break in this case");

    It it_;

    template <class U> friend class three_way_contiguous_iterator;
public:
    typedef          std::contiguous_iterator_tag              iterator_category;
    typedef typename std::iterator_traits<It>::value_type      value_type;
    typedef typename std::iterator_traits<It>::difference_type difference_type;
    typedef It                                                 pointer;
    typedef typename std::iterator_traits<It>::reference       reference;
    typedef typename std::remove_pointer<It>::type             element_type;

    constexpr It base() const {return it_;}

    constexpr three_way_contiguous_iterator() : it_() {}
    constexpr explicit three_way_contiguous_iterator(It it) : it_(it) {}
    template <class U>
    constexpr three_way_contiguous_iterator(const three_way_contiguous_iterator<U>& u) : it_(u.it_) {}

    constexpr reference operator*() const {return *it_;}
    constexpr pointer operator->() const {return it_;}

    constexpr three_way_contiguous_iterator& operator++() {++it_; return *this;}
    constexpr three_way_contiguous_iterator operator++(int) {auto tmp = *this; ++(*this); return tmp;}

    constexpr three_way_contiguous_iterator& operator--() {--it_; return *this;}
    constexpr three_way_contiguous_iterator operator--(int) {auto tmp = *this; --(*this); return tmp;}

    constexpr three_way_contiguous_iterator& operator+=(difference_type n) {it_ += n; return *this;}
    constexpr auto operator+(difference_type n) const {auto tmp = *this; tmp += n; return tmp;}
    friend constexpr auto operator+(difference_type n, three_way_contiguous_iterator x) {x += n; return x;}
    constexpr three_way_contiguous_iterator& operator-=(difference_type n) {return *this += -n;}
    constexpr auto operator-(difference_type n) const {auto tmp = *this; tmp -= n; return tmp;}

    constexpr reference operator[](difference_type n) const {return it_[n];}

    template <class T>
    void operator,(T const &) = delete;

    friend constexpr
    difference_type operator-(const three_way_contiguous_iterator& x, const three_way_contiguous_iterator& y) {
        return x.base() - y.base();
    }

    friend auto operator<=>(const three_way_contiguous_iterator&, const three_way_contiguous_iterator&) = default;
};

#endif // TEST_STD_VER > 17 && defined(__cpp_lib_concepts)

#endif // SUPPORT_TEST_ITERATORS_H