//
// Copyright (c) 2022 Slaven Falandys
//
// This software is provided 'as-is', without any express or implied
// warranty. In no event will the authors be held liable for any damages
// arising from the use of this software.
//
// Permission is granted to anyone to use this software for any purpose,
// including commercial applications, and to alter it and redistribute it
// freely, subject to the following restrictions:
//
// 1. The origin of this software must not be misrepresented; you must not
//    claim that you wrote the original software. If you use this software
//    in a product, an acknowledgment in the product documentation would be
//    appreciated but is not required.
// 2. Altered source versions must be plainly marked as such, and must not be
//    misrepresented as being the original software.
// 3. This notice may not be removed or altered from any source distribution.
//

#ifndef SFL_SMALL_VECTOR_HPP_INCLUDED
#define SFL_SMALL_VECTOR_HPP_INCLUDED

#include <sfl/detail/container_compatible_range.hpp>
#include <sfl/detail/cpp.hpp>
#include <sfl/detail/exceptions.hpp>
#include <sfl/detail/initialized_memory_algorithms.hpp>
#include <sfl/detail/normal_iterator.hpp>
#include <sfl/detail/tags.hpp>
#include <sfl/detail/to_address.hpp>
#include <sfl/detail/type_traits.hpp>
#include <sfl/detail/uninitialized_memory_algorithms.hpp>

#include <algorithm>        // copy, move, swap, swap_ranges
#include <cstddef>          // size_t
#include <initializer_list> // initializer_list
#include <iterator>         // distance, next, reverse_iterator
#include <limits>           // numeric_limits
#include <memory>           // allocator, allocator_traits, pointer_traits
#include <type_traits>      // is_same, is_nothrow_xxxxx
#include <utility>          // forward, move, pair

namespace sfl
{

template < typename T,
           std::size_t N,
           typename Allocator = std::allocator<T> >
class small_vector
{
public:

    using allocator_type         = Allocator;
    using allocator_traits       = std::allocator_traits<Allocator>;
    using value_type             = T;
    using size_type              = typename allocator_traits::size_type;
    using difference_type        = typename allocator_traits::difference_type;
    using reference              = T&;
    using const_reference        = const T&;
    using pointer                = typename allocator_traits::pointer;
    using const_pointer          = typename allocator_traits::const_pointer;
    using iterator               = sfl::dtl::normal_iterator<pointer, small_vector>;
    using const_iterator         = sfl::dtl::normal_iterator<const_pointer, small_vector>;
    using reverse_iterator       = std::reverse_iterator<iterator>;
    using const_reverse_iterator = std::reverse_iterator<const_iterator>;

    static_assert
    (
        std::is_same<typename Allocator::value_type, value_type>::value,
        "Allocator::value_type must be same as sfl::small_vector::value_type."
    );

public:

    static constexpr size_type static_capacity = N;

private:

    template <bool WithInternalStorage = true, typename = void>
    class data_base
    {
    private:

        union
        {
            value_type internal_storage_[N];
        };

    public:

        pointer first_;
        pointer last_;
        pointer eos_;

        data_base() noexcept
            : first_(std::pointer_traits<pointer>::pointer_to(*internal_storage_))
            , last_(first_)
            , eos_(first_ + N)
        {}

        ~data_base() noexcept
        {}

        pointer internal_storage() noexcept
        {
            return std::pointer_traits<pointer>::pointer_to(*internal_storage_);
        }
    };

    template <typename Dummy>
    class data_base<false, Dummy>
    {
    public:

        pointer first_;
        pointer last_;
        pointer eos_;

        data_base() noexcept
            : first_(nullptr)
            , last_(nullptr)
            , eos_(nullptr)
        {}

        pointer internal_storage() noexcept
        {
            return nullptr;
        }
    };

    class data : public data_base<(N > 0)> , public allocator_type
    {
    public:

        data() noexcept(std::is_nothrow_default_constructible<allocator_type>::value)
            : allocator_type()
        {}

        data(const allocator_type& alloc) noexcept(std::is_nothrow_copy_constructible<allocator_type>::value)
            : allocator_type(alloc)
        {}

        data(allocator_type&& other) noexcept(std::is_nothrow_move_constructible<allocator_type>::value)
            : allocator_type(std::move(other))
        {}

        allocator_type& ref_to_alloc() noexcept
        {
            return *this;
        }

        const allocator_type& ref_to_alloc() const noexcept
        {
            return *this;
        }
    };

    data data_;

public:

    //
    // ---- CONSTRUCTION AND DESTRUCTION --------------------------------------
    //

    small_vector() noexcept
    (
        std::is_nothrow_default_constructible<Allocator>::value
    )
        : data_()
    {}

    explicit small_vector(const Allocator& alloc) noexcept
    (
        std::is_nothrow_copy_constructible<Allocator>::value
    )
        : data_(alloc)
    {}

    small_vector(size_type n)
        : data_()
    {
        initialize_default_n(n);
    }

    explicit small_vector(size_type n, const Allocator& alloc)
        : data_(alloc)
    {
        initialize_default_n(n);
    }

    small_vector(size_type n, const T& value)
        : data_()
    {
        initialize_fill_n(n, value);
    }

    small_vector(size_type n, const T& value, const Allocator& alloc)
        : data_(alloc)
    {
        initialize_fill_n(n, value);
    }

    template <typename InputIt,
              sfl::dtl::enable_if_t<sfl::dtl::is_input_iterator<InputIt>::value>* = nullptr>
    small_vector(InputIt first, InputIt last)
        : data_()
    {
        initialize_range(first, last);
    }

    template <typename InputIt,
              sfl::dtl::enable_if_t<sfl::dtl::is_input_iterator<InputIt>::value>* = nullptr>
    small_vector(InputIt first, InputIt last, const Allocator& alloc)
        : data_(alloc)
    {
        initialize_range(first, last);
    }

    small_vector(std::initializer_list<T> ilist)
        : small_vector(ilist.begin(), ilist.end())
    {}

    small_vector(std::initializer_list<T> ilist, const Allocator& alloc)
        : small_vector(ilist.begin(), ilist.end(), alloc)
    {}

    small_vector(const small_vector& other)
        : data_
        (
            allocator_traits::select_on_container_copy_construction
            (
                other.data_.ref_to_alloc()
            )
        )
    {
        initialize_copy(other);
    }

    small_vector(const small_vector& other, const Allocator& alloc)
        : data_(alloc)
    {
        initialize_copy(other);
    }

    small_vector(small_vector&& other)
        : data_(std::move(other.data_.ref_to_alloc()))
    {
        initialize_move(other);
    }

    small_vector(small_vector&& other, const Allocator& alloc)
        : data_(alloc)
    {
        initialize_move(other);
    }

#if SFL_CPP_VERSION >= SFL_CPP_20

    template <sfl::dtl::container_compatible_range<value_type> Range>
    small_vector(sfl::from_range_t, Range&& range)
        : data_()
    {
        initialize_range(std::forward<Range>(range));
    }

    template <sfl::dtl::container_compatible_range<value_type> Range>
    small_vector(sfl::from_range_t, Range&& range, const Allocator& alloc)
        : data_(alloc)
    {
        initialize_range(std::forward<Range>(range));
    }

#else // before C++20

    template <typename Range>
    small_vector(sfl::from_range_t, Range&& range)
        : data_()
    {
        initialize_range(std::forward<Range>(range));
    }

    template <typename Range>
    small_vector(sfl::from_range_t, Range&& range, const Allocator& alloc)
        : data_(alloc)
    {
        initialize_range(std::forward<Range>(range));
    }

#endif // before C++20

    ~small_vector()
    {
        sfl::dtl::destroy_a
        (
            data_.ref_to_alloc(),
            data_.first_,
            data_.last_
        );

        if (data_.first_ != data_.internal_storage())
        {
            sfl::dtl::deallocate
            (
                data_.ref_to_alloc(),
                data_.first_,
                std::distance(data_.first_, data_.eos_)
            );
        }
    }

    //
    // ---- ASSIGNMENT --------------------------------------------------------
    //

    void assign(size_type n, const T& value)
    {
        assign_fill_n(n, value);
    }

    template <typename InputIt,
              sfl::dtl::enable_if_t<sfl::dtl::is_input_iterator<InputIt>::value>* = nullptr>
    void assign(InputIt first, InputIt last)
    {
        assign_range(first, last);
    }

    void assign(std::initializer_list<T> ilist)
    {
        assign_range(ilist.begin(), ilist.end());
    }

#if SFL_CPP_VERSION >= SFL_CPP_20

    template <sfl::dtl::container_compatible_range<value_type> Range>
    void assign_range(Range&& range)
    {
        if constexpr (std::ranges::forward_range<Range>)
        {
            assign_range(std::ranges::begin(range), std::ranges::end(range), std::forward_iterator_tag());
        }
        else
        {
            assign_range(std::ranges::begin(range), std::ranges::end(range), std::input_iterator_tag());
        }
    }

#else // before C++20

    template <typename Range>
    void assign_range(Range&& range)
    {
        using std::begin;
        using std::end;
        assign_range(begin(range), end(range));
    }

#endif // before C++20

    small_vector& operator=(const small_vector& other)
    {
        assign_copy(other);
        return *this;
    }

    small_vector& operator=(small_vector&& other)
    {
        assign_move(other);
        return *this;
    }

    small_vector& operator=(std::initializer_list<T> ilist)
    {
        assign_range(ilist.begin(), ilist.end());
        return *this;
    }

    //
    // ---- ALLOCATOR ---------------------------------------------------------
    //

    SFL_NODISCARD
    allocator_type get_allocator() const noexcept
    {
        return data_.ref_to_alloc();
    }

    //
    // ---- ITERATORS ---------------------------------------------------------
    //

    SFL_NODISCARD
    iterator begin() noexcept
    {
        return iterator(data_.first_);
    }

    SFL_NODISCARD
    const_iterator begin() const noexcept
    {
        return const_iterator(data_.first_);
    }

    SFL_NODISCARD
    const_iterator cbegin() const noexcept
    {
        return const_iterator(data_.first_);
    }

    SFL_NODISCARD
    iterator end() noexcept
    {
        return iterator(data_.last_);
    }

    SFL_NODISCARD
    const_iterator end() const noexcept
    {
        return const_iterator(data_.last_);
    }

    SFL_NODISCARD
    const_iterator cend() const noexcept
    {
        return const_iterator(data_.last_);
    }

    SFL_NODISCARD
    reverse_iterator rbegin() noexcept
    {
        return reverse_iterator(end());
    }

    SFL_NODISCARD
    const_reverse_iterator rbegin() const noexcept
    {
        return const_reverse_iterator(end());
    }

    SFL_NODISCARD
    const_reverse_iterator crbegin() const noexcept
    {
        return const_reverse_iterator(end());
    }

    SFL_NODISCARD
    reverse_iterator rend() noexcept
    {
        return reverse_iterator(begin());
    }

    SFL_NODISCARD
    const_reverse_iterator rend() const noexcept
    {
        return const_reverse_iterator(begin());
    }

    SFL_NODISCARD
    const_reverse_iterator crend() const noexcept
    {
        return const_reverse_iterator(begin());
    }

    SFL_NODISCARD
    iterator nth(size_type pos) noexcept
    {
        SFL_ASSERT(pos <= size());
        return iterator(data_.first_ + pos);
    }

    SFL_NODISCARD
    const_iterator nth(size_type pos) const noexcept
    {
        SFL_ASSERT(pos <= size());
        return const_iterator(data_.first_ + pos);
    }

    SFL_NODISCARD
    size_type index_of(const_iterator pos) const noexcept
    {
        SFL_ASSERT(cbegin() <= pos && pos <= cend());
        return std::distance(cbegin(), pos);
    }

    //
    // ---- SIZE AND CAPACITY -------------------------------------------------
    //

    SFL_NODISCARD
    bool empty() const noexcept
    {
        return data_.first_ == data_.last_;
    }

    SFL_NODISCARD
    size_type size() const noexcept
    {
        return std::distance(data_.first_, data_.last_);
    }

    SFL_NODISCARD
    size_type max_size() const noexcept
    {
        return std::min<size_type>
        (
            allocator_traits::max_size(data_.ref_to_alloc()),
            std::numeric_limits<difference_type>::max() / sizeof(value_type)
        );
    }

    SFL_NODISCARD
    size_type capacity() const noexcept
    {
        return std::distance(data_.first_, data_.eos_);
    }

    SFL_NODISCARD
    size_type available() const noexcept
    {
        return std::distance(data_.last_, data_.eos_);
    }

    void reserve(size_type new_cap)
    {
        check_size(new_cap, "sfl::small_vector::reserve");

        if (new_cap > capacity())
        {
            if (new_cap <= N)
            {
                if (data_.first_ == data_.internal_storage())
                {
                    // Do nothing. We are already using internal storage.
                }
                else
                {
                    // We are not using internal storage but new capacity
                    // can fit in internal storage.

                    pointer new_first = data_.internal_storage();
                    pointer new_last  = new_first;
                    pointer new_eos   = new_first + N;

                    new_last = sfl::dtl::uninitialized_move_if_noexcept_a
                    (
                        data_.ref_to_alloc(),
                        data_.first_,
                        data_.last_,
                        new_first
                    );

                    sfl::dtl::destroy_a
                    (
                        data_.ref_to_alloc(),
                        data_.first_,
                        data_.last_
                    );

                    sfl::dtl::deallocate
                    (
                        data_.ref_to_alloc(),
                        data_.first_,
                        std::distance(data_.first_, data_.eos_)
                    );

                    data_.first_ = new_first;
                    data_.last_  = new_last;
                    data_.eos_   = new_eos;
                }
            }
            else
            {
                pointer new_first = sfl::dtl::allocate(data_.ref_to_alloc(), new_cap);
                pointer new_last  = new_first;
                pointer new_eos   = new_first + new_cap;

                SFL_TRY
                {
                    new_last = sfl::dtl::uninitialized_move_if_noexcept_a
                    (
                        data_.ref_to_alloc(),
                        data_.first_,
                        data_.last_,
                        new_first
                    );
                }
                SFL_CATCH (...)
                {
                    sfl::dtl::deallocate
                    (
                        data_.ref_to_alloc(),
                        new_first,
                        new_cap
                    );

                    SFL_RETHROW;
                }

                sfl::dtl::destroy_a
                (
                    data_.ref_to_alloc(),
                    data_.first_,
                    data_.last_
                );

                if (data_.first_ != data_.internal_storage())
                {
                    sfl::dtl::deallocate
                    (
                        data_.ref_to_alloc(),
                        data_.first_,
                        std::distance(data_.first_, data_.eos_)
                    );
                }

                data_.first_ = new_first;
                data_.last_  = new_last;
                data_.eos_   = new_eos;
            }
        }
    }

    void shrink_to_fit()
    {
        const size_type new_cap = size();

        if (new_cap < capacity())
        {
            if (new_cap <= N)
            {
                if (data_.first_ == data_.internal_storage())
                {
                    // Do nothing. We are already using internal storage.
                }
                else
                {
                    // We are not using internal storage but new capacity
                    // can fit in internal storage.

                    pointer new_first = data_.internal_storage();
                    pointer new_last  = new_first;
                    pointer new_eos   = new_first + N;

                    new_last = sfl::dtl::uninitialized_move_if_noexcept_a
                    (
                        data_.ref_to_alloc(),
                        data_.first_,
                        data_.last_,
                        new_first
                    );

                    sfl::dtl::destroy_a
                    (
                        data_.ref_to_alloc(),
                        data_.first_,
                        data_.last_
                    );

                    sfl::dtl::deallocate
                    (
                        data_.ref_to_alloc(),
                        data_.first_,
                        std::distance(data_.first_, data_.eos_)
                    );

                    data_.first_ = new_first;
                    data_.last_  = new_last;
                    data_.eos_   = new_eos;
                }
            }
            else
            {
                pointer new_first = sfl::dtl::allocate(data_.ref_to_alloc(), new_cap);
                pointer new_last  = new_first;
                pointer new_eos   = new_first + new_cap;

                SFL_TRY
                {
                    new_last = sfl::dtl::uninitialized_move_if_noexcept_a
                    (
                        data_.ref_to_alloc(),
                        data_.first_,
                        data_.last_,
                        new_first
                    );
                }
                SFL_CATCH (...)
                {
                    sfl::dtl::deallocate
                    (
                        data_.ref_to_alloc(),
                        new_first,
                        new_cap
                    );

                    SFL_RETHROW;
                }

                sfl::dtl::destroy_a
                (
                    data_.ref_to_alloc(),
                    data_.first_,
                    data_.last_
                );

                if (data_.first_ != data_.internal_storage())
                {
                    sfl::dtl::deallocate
                    (
                        data_.ref_to_alloc(),
                        data_.first_,
                        std::distance(data_.first_, data_.eos_)
                    );
                }

                data_.first_ = new_first;
                data_.last_  = new_last;
                data_.eos_   = new_eos;
            }
        }
    }

    //
    // ---- ELEMENT ACCESS ----------------------------------------------------
    //

    SFL_NODISCARD
    reference at(size_type pos)
    {
        if (pos >= size())
        {
            sfl::dtl::throw_out_of_range("sfl::small_vector::at");
        }

        return *(data_.first_ + pos);
    }

    SFL_NODISCARD
    const_reference at(size_type pos) const
    {
        if (pos >= size())
        {
            sfl::dtl::throw_out_of_range("sfl::small_vector::at");
        }

        return *(data_.first_ + pos);
    }

    SFL_NODISCARD
    reference operator[](size_type pos) noexcept
    {
        SFL_ASSERT(pos < size());
        return *(data_.first_ + pos);
    }

    SFL_NODISCARD
    const_reference operator[](size_type pos) const noexcept
    {
        SFL_ASSERT(pos < size());
        return *(data_.first_ + pos);
    }

    SFL_NODISCARD
    reference front() noexcept
    {
        SFL_ASSERT(!empty());
        return *data_.first_;
    }

    SFL_NODISCARD
    const_reference front() const noexcept
    {
        SFL_ASSERT(!empty());
        return *data_.first_;
    }

    SFL_NODISCARD
    reference back() noexcept
    {
        SFL_ASSERT(!empty());
        return *(data_.last_ - 1);
    }

    SFL_NODISCARD
    const_reference back() const noexcept
    {
        SFL_ASSERT(!empty());
        return *(data_.last_ - 1);
    }

    SFL_NODISCARD
    T* data() noexcept
    {
        return sfl::dtl::to_address(data_.first_);
    }

    SFL_NODISCARD
    const T* data() const noexcept
    {
        return sfl::dtl::to_address(data_.first_);
    }

    //
    // ---- MODIFIERS ---------------------------------------------------------
    //

    void clear() noexcept
    {
        sfl::dtl::destroy_a
        (
            data_.ref_to_alloc(),
            data_.first_,
            data_.last_
        );

        data_.last_ = data_.first_;
    }

    template <typename... Args>
    iterator emplace(const_iterator pos, Args&&... args)
    {
        SFL_ASSERT(cbegin() <= pos && pos <= cend());

        if (data_.last_ != data_.eos_)
        {
            const pointer p1 = data_.first_ + std::distance(cbegin(), pos);

            if (p1 == data_.last_)
            {
                sfl::dtl::construct_at_a
                (
                    data_.ref_to_alloc(),
                    p1,
                    std::forward<Args>(args)...
                );

                ++data_.last_;
            }
            else
            {
                // This container can contain duplicates so we must
                // create new element now as a temporary value.
                value_type tmp(std::forward<Args>(args)...);

                const pointer p2 = data_.last_ - 1;

                const pointer old_last = data_.last_;

                sfl::dtl::construct_at_a
                (
                    data_.ref_to_alloc(),
                    data_.last_,
                    std::move(*p2)
                );

                ++data_.last_;

                sfl::dtl::move_backward
                (
                    p1,
                    p2,
                    old_last
                );

                *p1 = std::move(tmp);
            }

            return iterator(p1);
        }
        else
        {
            const difference_type offset = std::distance(cbegin(), pos);

            const size_type new_cap =
                calculate_new_capacity(1, "sfl::small_vector::emplace");

            pointer new_first;
            pointer new_last;
            pointer new_eos;

            if (new_cap <= N && data_.first_ != data_.internal_storage())
            {
                new_first = data_.internal_storage();
                new_last  = new_first;
                new_eos   = new_first + N;
            }
            else
            {
                new_first = sfl::dtl::allocate(data_.ref_to_alloc(), new_cap);
                new_last  = new_first;
                new_eos   = new_first + new_cap;
            }

            const pointer p = new_first + offset;

            SFL_TRY
            {
                sfl::dtl::construct_at_a
                (
                    data_.ref_to_alloc(),
                    p,
                    std::forward<Args>(args)...
                );

                new_last = nullptr;

                const pointer mid = data_.first_ + offset;

                new_last = sfl::dtl::uninitialized_move_if_noexcept_a
                (
                    data_.ref_to_alloc(),
                    data_.first_,
                    mid,
                    new_first
                );

                ++new_last;

                new_last = sfl::dtl::uninitialized_move_if_noexcept_a
                (
                    data_.ref_to_alloc(),
                    mid,
                    data_.last_,
                    new_last
                );
            }
            SFL_CATCH (...)
            {
                if (new_last == nullptr)
                {
                    sfl::dtl::destroy_at_a
                    (
                        data_.ref_to_alloc(),
                        p
                    );
                }
                else
                {
                    sfl::dtl::destroy_a
                    (
                        data_.ref_to_alloc(),
                        new_first,
                        new_last
                    );
                }

                if (new_first != data_.internal_storage())
                {
                    sfl::dtl::deallocate
                    (
                        data_.ref_to_alloc(),
                        new_first,
                        new_cap
                    );
                }

                SFL_RETHROW;
            }

            sfl::dtl::destroy_a
            (
                data_.ref_to_alloc(),
                data_.first_,
                data_.last_
            );

            if (data_.first_ != data_.internal_storage())
            {
                sfl::dtl::deallocate
                (
                    data_.ref_to_alloc(),
                    data_.first_,
                    std::distance(data_.first_, data_.eos_)
                );
            }

            data_.first_ = new_first;
            data_.last_  = new_last;
            data_.eos_   = new_eos;

            return iterator(p);
        }
    }

    iterator insert(const_iterator pos, const T& value)
    {
        SFL_ASSERT(cbegin() <= pos && pos <= cend());
        return emplace(pos, value);
    }

    iterator insert(const_iterator pos, T&& value)
    {
        SFL_ASSERT(cbegin() <= pos && pos <= cend());
        return emplace(pos, std::move(value));
    }

    iterator insert(const_iterator pos, size_type n, const T& value)
    {
        SFL_ASSERT(cbegin() <= pos && pos <= cend());
        return insert_fill_n(pos, n, value);
    }

    template <typename InputIt,
              sfl::dtl::enable_if_t<sfl::dtl::is_input_iterator<InputIt>::value>* = nullptr>
    iterator insert(const_iterator pos, InputIt first, InputIt last)
    {
        SFL_ASSERT(cbegin() <= pos && pos <= cend());
        return insert_range(pos, first, last);
    }

    iterator insert(const_iterator pos, std::initializer_list<T> ilist)
    {
        SFL_ASSERT(cbegin() <= pos && pos <= cend());
        return insert_range(pos, ilist.begin(), ilist.end());
    }

#if SFL_CPP_VERSION >= SFL_CPP_20

    template <sfl::dtl::container_compatible_range<value_type> Range>
    iterator insert_range(const_iterator pos, Range&& range)
    {
        SFL_ASSERT(cbegin() <= pos && pos <= cend());
        if constexpr (std::ranges::forward_range<Range>)
        {
            return insert_range(pos, std::ranges::begin(range), std::ranges::end(range), std::forward_iterator_tag());
        }
        else
        {
            return insert_range(pos, std::ranges::begin(range), std::ranges::end(range), std::input_iterator_tag());
        }
    }

#else // before C++20

    template <typename Range>
    iterator insert_range(const_iterator pos, Range&& range)
    {
        SFL_ASSERT(cbegin() <= pos && pos <= cend());
        using std::begin;
        using std::end;
        return insert_range(pos, begin(range), end(range));
    }

#endif // before C++20

    template <typename... Args>
    reference emplace_back(Args&&... args)
    {
        if (data_.last_ != data_.eos_)
        {
            const pointer old_last = data_.last_;

            sfl::dtl::construct_at_a
            (
                data_.ref_to_alloc(),
                data_.last_,
                std::forward<Args>(args)...
            );

            ++data_.last_;

            return *old_last;
        }
        else
        {
            const size_type new_cap =
                calculate_new_capacity(1, "sfl::small_vector::emplace_back");

            pointer new_first;
            pointer new_last;
            pointer new_eos;

            if (new_cap <= N && data_.first_ != data_.internal_storage())
            {
                new_first = data_.internal_storage();
                new_last  = new_first;
                new_eos   = new_first + N;
            }
            else
            {
                new_first = sfl::dtl::allocate(data_.ref_to_alloc(), new_cap);
                new_last  = new_first;
                new_eos   = new_first + new_cap;
            }

            const pointer p = new_first + size();

            SFL_TRY
            {
                sfl::dtl::construct_at_a
                (
                    data_.ref_to_alloc(),
                    p,
                    std::forward<Args>(args)...
                );

                new_last = nullptr;

                new_last = sfl::dtl::uninitialized_move_if_noexcept_a
                (
                    data_.ref_to_alloc(),
                    data_.first_,
                    data_.last_,
                    new_first
                );

                ++new_last;
            }
            SFL_CATCH (...)
            {
                if (new_last == nullptr)
                {
                    sfl::dtl::destroy_at_a
                    (
                        data_.ref_to_alloc(),
                        p
                    );
                }
                else
                {
                    // Nothing to do
                }

                if (new_first != data_.internal_storage())
                {
                    sfl::dtl::deallocate
                    (
                        data_.ref_to_alloc(),
                        new_first,
                        new_cap
                    );
                }

                SFL_RETHROW;
            }

            sfl::dtl::destroy_a
            (
                data_.ref_to_alloc(),
                data_.first_,
                data_.last_
            );

            if (data_.first_ != data_.internal_storage())
            {
                sfl::dtl::deallocate
                (
                    data_.ref_to_alloc(),
                    data_.first_,
                    std::distance(data_.first_, data_.eos_)
                );
            }

            data_.first_ = new_first;
            data_.last_  = new_last;
            data_.eos_   = new_eos;

            return *p;
        }
    }

    void push_back(const T& value)
    {
        emplace_back(value);
    }

    void push_back(T&& value)
    {
        emplace_back(std::move(value));
    }

#if SFL_CPP_VERSION >= SFL_CPP_20

    template <sfl::dtl::container_compatible_range<value_type> Range>
    void append_range(Range&& range)
    {
        insert_range(end(), std::forward<Range>(range));
    }

#else // before C++20

    template <typename Range>
    void append_range(Range&& range)
    {
        insert_range(end(), std::forward<Range>(range));
    }

#endif // before C++20

    void pop_back()
    {
        SFL_ASSERT(!empty());

        --data_.last_;

        sfl::dtl::destroy_at_a(data_.ref_to_alloc(), data_.last_);
    }

    iterator erase(const_iterator pos)
    {
        SFL_ASSERT(cbegin() <= pos && pos < cend());

        const pointer p = data_.first_ + std::distance(cbegin(), pos);

        data_.last_ = sfl::dtl::move(p + 1, data_.last_, p);

        sfl::dtl::destroy_at_a(data_.ref_to_alloc(), data_.last_);

        return iterator(p);
    }

    iterator erase(const_iterator first, const_iterator last)
    {
        SFL_ASSERT(cbegin() <= first && first <= last && last <= cend());

        if (first == last)
        {
            return begin() + std::distance(cbegin(), first);
        }

        const pointer p1 = data_.first_ + std::distance(cbegin(), first);
        const pointer p2 = data_.first_ + std::distance(cbegin(), last);

        const pointer new_last = sfl::dtl::move(p2, data_.last_, p1);

        sfl::dtl::destroy_a(data_.ref_to_alloc(), new_last, data_.last_);

        data_.last_ = new_last;

        return iterator(p1);
    }

    void resize(size_type n)
    {
        check_size(n, "sfl::small_vector::resize");

        const size_type size = this->size();

        if (n < size)
        {
            const pointer new_last = data_.first_ + n;

            sfl::dtl::destroy_a
            (
                data_.ref_to_alloc(),
                new_last,
                data_.last_
            );

            data_.last_ = new_last;
        }
        else if (n > size)
        {
            const size_type delta = n - size;

            if (n > capacity())
            {
                pointer new_first;
                pointer new_last;
                pointer new_eos;

                if (n <= N && data_.first_ != data_.internal_storage())
                {
                    new_first = data_.internal_storage();
                    new_last  = new_first;
                    new_eos   = new_first + N;
                }
                else
                {
                    new_first = sfl::dtl::allocate(data_.ref_to_alloc(), n);
                    new_last  = new_first;
                    new_eos   = new_first + n;
                }

                SFL_TRY
                {
                    sfl::dtl::uninitialized_default_construct_n_a
                    (
                        data_.ref_to_alloc(),
                        new_first + size,
                        delta
                    );

                    new_last = nullptr;

                    new_last = sfl::dtl::uninitialized_move_if_noexcept_a
                    (
                        data_.ref_to_alloc(),
                        data_.first_,
                        data_.last_,
                        new_first
                    );

                    new_last += delta;
                }
                SFL_CATCH (...)
                {
                    if (new_last == nullptr)
                    {
                        sfl::dtl::destroy_n_a
                        (
                            data_.ref_to_alloc(),
                            new_first + size,
                            delta
                        );
                    }
                    else
                    {
                        sfl::dtl::destroy_a
                        (
                            data_.ref_to_alloc(),
                            new_first,
                            new_last
                        );
                    }

                    if (new_first != data_.internal_storage())
                    {
                        sfl::dtl::deallocate
                        (
                            data_.ref_to_alloc(),
                            new_first,
                            n
                        );
                    }

                    SFL_RETHROW;
                }

                sfl::dtl::destroy_a
                (
                    data_.ref_to_alloc(),
                    data_.first_,
                    data_.last_
                );

                if (data_.first_ != data_.internal_storage())
                {
                    sfl::dtl::deallocate
                    (
                        data_.ref_to_alloc(),
                        data_.first_,
                        std::distance(data_.first_, data_.eos_)
                    );
                }

                data_.first_ = new_first;
                data_.last_  = new_last;
                data_.eos_   = new_eos;
            }
            else
            {
                data_.last_ = sfl::dtl::uninitialized_default_construct_n_a
                (
                    data_.ref_to_alloc(),
                    data_.last_,
                    delta
                );
            }
        }
    }

    void resize(size_type n, const T& value)
    {
        check_size(n, "sfl::small_vector::resize");

        const size_type size = this->size();

        if (n < size)
        {
            const pointer new_last = data_.first_ + n;

            sfl::dtl::destroy_a
            (
                data_.ref_to_alloc(),
                new_last,
                data_.last_
            );

            data_.last_ = new_last;
        }
        else if (n > size)
        {
            const size_type delta = n - size;

            if (n > capacity())
            {
                pointer new_first;
                pointer new_last;
                pointer new_eos;

                if (n <= N && data_.first_ != data_.internal_storage())
                {
                    new_first = data_.internal_storage();
                    new_last  = new_first;
                    new_eos   = new_first + N;
                }
                else
                {
                    new_first = sfl::dtl::allocate(data_.ref_to_alloc(), n);
                    new_last  = new_first;
                    new_eos   = new_first + n;
                }

                SFL_TRY
                {
                    sfl::dtl::uninitialized_fill_n_a
                    (
                        data_.ref_to_alloc(),
                        new_first + size,
                        delta,
                        value
                    );

                    new_last = nullptr;

                    new_last = sfl::dtl::uninitialized_move_if_noexcept_a
                    (
                        data_.ref_to_alloc(),
                        data_.first_,
                        data_.last_,
                        new_first
                    );

                    new_last += delta;
                }
                SFL_CATCH (...)
                {
                    if (new_last == nullptr)
                    {
                        sfl::dtl::destroy_n_a
                        (
                            data_.ref_to_alloc(),
                            new_first + size,
                            delta
                        );
                    }
                    else
                    {
                        sfl::dtl::destroy_a
                        (
                            data_.ref_to_alloc(),
                            new_first,
                            new_last
                        );
                    }

                    if (new_first != data_.internal_storage())
                    {
                        sfl::dtl::deallocate
                        (
                            data_.ref_to_alloc(),
                            new_first,
                            n
                        );
                    }

                    SFL_RETHROW;
                }

                sfl::dtl::destroy_a
                (
                    data_.ref_to_alloc(),
                    data_.first_,
                    data_.last_
                );

                if (data_.first_ != data_.internal_storage())
                {
                    sfl::dtl::deallocate
                    (
                        data_.ref_to_alloc(),
                        data_.first_,
                        std::distance(data_.first_, data_.eos_)
                    );
                }

                data_.first_ = new_first;
                data_.last_  = new_last;
                data_.eos_   = new_eos;
            }
            else
            {
                data_.last_ = sfl::dtl::uninitialized_fill_n_a
                (
                    data_.ref_to_alloc(),
                    data_.last_,
                    delta,
                    value
                );
            }
        }
    }

    void swap(small_vector& other)
    {
        if (this == &other)
        {
            return;
        }

        using std::swap;

        SFL_ASSERT
        (
            allocator_traits::propagate_on_container_swap::value ||
            this->data_.ref_to_alloc() == other.data_.ref_to_alloc()
        );

        // If this and other allocator compares equal then one allocator
        // can deallocate memory allocated by another allocator.
        // One allocator can safely destroy_a elements constructed by other
        // allocator regardless the two allocators compare equal or not.

        if (allocator_traits::propagate_on_container_swap::value)
        {
            swap(this->data_.ref_to_alloc(), other.data_.ref_to_alloc());
        }

        if
        (
            this->data_.first_ == this->data_.internal_storage() &&
            other.data_.first_ == other.data_.internal_storage()
        )
        {
            const size_type this_size  = this->size();
            const size_type other_size = other.size();

            if (this_size <= other_size)
            {
                std::swap_ranges
                (
                    this->data_.first_,
                    this->data_.first_ + this_size,
                    other.data_.first_
                );

                sfl::dtl::uninitialized_move_a
                (
                    this->data_.ref_to_alloc(),
                    other.data_.first_ + this_size,
                    other.data_.first_ + other_size,
                    this->data_.first_ + this_size
                );

                sfl::dtl::destroy_a
                (
                    other.data_.ref_to_alloc(),
                    other.data_.first_ + this_size,
                    other.data_.first_ + other_size
                );
            }
            else
            {
                std::swap_ranges
                (
                    other.data_.first_,
                    other.data_.first_ + other_size,
                    this->data_.first_
                );

                sfl::dtl::uninitialized_move_a
                (
                    other.data_.ref_to_alloc(),
                    this->data_.first_ + other_size,
                    this->data_.first_ + this_size,
                    other.data_.first_ + other_size
                );

                sfl::dtl::destroy_a
                (
                    this->data_.ref_to_alloc(),
                    this->data_.first_ + other_size,
                    this->data_.first_ + this_size
                );
            }

            this->data_.last_ = this->data_.first_ + other_size;
            other.data_.last_ = other.data_.first_ + this_size;
        }
        else if
        (
            this->data_.first_ == this->data_.internal_storage() &&
            other.data_.first_ != other.data_.internal_storage()
        )
        {
            pointer new_other_first = other.data_.internal_storage();
            pointer new_other_last  = new_other_first;
            pointer new_other_eos   = new_other_first + N;

            new_other_last = sfl::dtl::uninitialized_move_a
            (
                other.data_.ref_to_alloc(),
                this->data_.first_,
                this->data_.last_,
                new_other_first
            );

            sfl::dtl::destroy_a
            (
                this->data_.ref_to_alloc(),
                this->data_.first_,
                this->data_.last_
            );

            this->data_.first_ = other.data_.first_;
            this->data_.last_  = other.data_.last_;
            this->data_.eos_   = other.data_.eos_;

            other.data_.first_ = new_other_first;
            other.data_.last_  = new_other_last;
            other.data_.eos_   = new_other_eos;
        }
        else if
        (
            this->data_.first_ != this->data_.internal_storage() &&
            other.data_.first_ == other.data_.internal_storage()
        )
        {
            pointer new_this_first = this->data_.internal_storage();
            pointer new_this_last  = new_this_first;
            pointer new_this_eos   = new_this_first + N;

            new_this_last = sfl::dtl::uninitialized_move_a
            (
                this->data_.ref_to_alloc(),
                other.data_.first_,
                other.data_.last_,
                new_this_first
            );

            sfl::dtl::destroy_a
            (
                other.data_.ref_to_alloc(),
                other.data_.first_,
                other.data_.last_
            );

            other.data_.first_ = this->data_.first_;
            other.data_.last_  = this->data_.last_;
            other.data_.eos_   = this->data_.eos_;

            this->data_.first_ = new_this_first;
            this->data_.last_  = new_this_last;
            this->data_.eos_   = new_this_eos;
        }
        else
        {
            swap(this->data_.first_, other.data_.first_);
            swap(this->data_.last_,  other.data_.last_);
            swap(this->data_.eos_,   other.data_.eos_);
        }
    }

private:

    void check_size(size_type n, const char* msg)
    {
        if (n > max_size())
        {
            sfl::dtl::throw_length_error(msg);
        }
    }

    size_type calculate_new_capacity(size_type num_additional_elements, const char* msg)
    {
        const size_type size = this->size();
        const size_type capacity = this->capacity();
        const size_type max_size = this->max_size();

        if (max_size - size < num_additional_elements)
        {
            sfl::dtl::throw_length_error(msg);
        }
        else if (max_size - capacity < capacity / 2)
        {
            return max_size;
        }
        else if (size + num_additional_elements < capacity + capacity / 2)
        {
            return std::max(N, capacity + capacity / 2);
        }
        else
        {
            return std::max(N, size + num_additional_elements);
        }
    }

    void reset(size_type new_cap = N)
    {
        sfl::dtl::destroy_a
        (
            data_.ref_to_alloc(),
            data_.first_,
            data_.last_
        );

        if (data_.first_ != data_.internal_storage())
        {
            sfl::dtl::deallocate
            (
                data_.ref_to_alloc(),
                data_.first_,
                std::distance(data_.first_, data_.eos_)
            );
        }

        data_.first_ = data_.internal_storage();
        data_.last_  = data_.first_;
        data_.eos_   = data_.first_ + N;

        if (new_cap > N)
        {
            data_.first_ = sfl::dtl::allocate(data_.ref_to_alloc(), new_cap);
            data_.last_  = data_.first_;
            data_.eos_   = data_.first_ + new_cap;

            // If allocation throws, first_, last_ and eos_ will be valid
            // (they will be pointing to internal_storage).
        }
    }

    void initialize_default_n(size_type n)
    {
        check_size(n, "sfl::small_vector::initialize_default_n");

        if (n > N)
        {
            data_.first_ = sfl::dtl::allocate(data_.ref_to_alloc(), n);
            data_.last_  = data_.first_;
            data_.eos_   = data_.first_ + n;
        }

        SFL_TRY
        {
            data_.last_ = sfl::dtl::uninitialized_default_construct_n_a
            (
                data_.ref_to_alloc(),
                data_.first_,
                n
            );
        }
        SFL_CATCH (...)
        {
            if (n > N)
            {
                sfl::dtl::deallocate(data_.ref_to_alloc(), data_.first_, n);
            }

            SFL_RETHROW;
        }
    }

    void initialize_fill_n(size_type n, const T& value)
    {
        check_size(n, "sfl::small_vector::initialize_fill_n");

        if (n > N)
        {
            data_.first_ = sfl::dtl::allocate(data_.ref_to_alloc(), n);
            data_.last_  = data_.first_;
            data_.eos_   = data_.first_ + n;
        }

        SFL_TRY
        {
            data_.last_ = sfl::dtl::uninitialized_fill_n_a
            (
                data_.ref_to_alloc(),
                data_.first_,
                n,
                value
            );
        }
        SFL_CATCH (...)
        {
            if (n > N)
            {
                sfl::dtl::deallocate(data_.ref_to_alloc(), data_.first_, n);
            }

            SFL_RETHROW;
        }
    }

    template <typename InputIt>
    void initialize_range(InputIt first, InputIt last)
    {
        initialize_range(first, last, typename std::iterator_traits<InputIt>::iterator_category());
    }

    template <typename InputIt, typename Sentinel>
    void initialize_range(InputIt first, Sentinel last, std::input_iterator_tag)
    {
        SFL_TRY
        {
            while (first != last)
            {
                emplace_back(*first);
                ++first;
            }
        }
        SFL_CATCH (...)
        {
            sfl::dtl::destroy_a
            (
                data_.ref_to_alloc(),
                data_.first_,
                data_.last_
            );

            if (data_.first_ != data_.internal_storage())
            {
                sfl::dtl::deallocate
                (
                    data_.ref_to_alloc(),
                    data_.first_,
                    std::distance(data_.first_, data_.eos_)
                );
            }

            SFL_RETHROW;
        }
    }

    template <typename ForwardIt, typename Sentinel>
    void initialize_range(ForwardIt first, Sentinel last, std::forward_iterator_tag)
    {
        const size_type n = std::distance(first, last);

        check_size(n, "sfl::small_vector::initialize_range");

        if (n > N)
        {
            data_.first_ = sfl::dtl::allocate(data_.ref_to_alloc(), n);
            data_.last_  = data_.first_;
            data_.eos_   = data_.first_ + n;
        }

        SFL_TRY
        {
            data_.last_ = sfl::dtl::uninitialized_copy_a
            (
                data_.ref_to_alloc(),
                first,
                last,
                data_.first_
            );
        }
        SFL_CATCH (...)
        {
            if (n > N)
            {
                sfl::dtl::deallocate(data_.ref_to_alloc(), data_.first_, n);
            }

            SFL_RETHROW;
        }
    }

#if SFL_CPP_VERSION >= SFL_CPP_20

    template <sfl::dtl::container_compatible_range<value_type> Range>
    void initialize_range(Range&& range)
    {
        if constexpr (std::ranges::forward_range<Range>)
        {
            initialize_range(std::ranges::begin(range), std::ranges::end(range), std::forward_iterator_tag());
        }
        else
        {
            initialize_range(std::ranges::begin(range), std::ranges::end(range), std::input_iterator_tag());
        }
    }

#else // before C++20

    template <typename Range>
    void initialize_range(Range&& range)
    {
        using std::begin;
        using std::end;
        initialize_range(begin(range), end(range));
    }

#endif // before C++20

    void initialize_copy(const small_vector& other)
    {
        const size_type n = other.size();

        check_size(n, "sfl::small_vector::initialize_copy");

        if (n > N)
        {
            data_.first_ = sfl::dtl::allocate(data_.ref_to_alloc(), n);
            data_.last_  = data_.first_;
            data_.eos_   = data_.first_ + n;
        }

        SFL_TRY
        {
            data_.last_ = sfl::dtl::uninitialized_copy_a
            (
                data_.ref_to_alloc(),
                other.data_.first_,
                other.data_.last_,
                data_.first_
            );
        }
        SFL_CATCH (...)
        {
            if (n > N)
            {
                sfl::dtl::deallocate(data_.ref_to_alloc(), data_.first_, n);
            }

            SFL_RETHROW;
        }
    }

    void initialize_move(small_vector& other)
    {
        if (other.data_.first_ == other.data_.internal_storage())
        {
            data_.last_ = sfl::dtl::uninitialized_move_a
            (
                data_.ref_to_alloc(),
                other.data_.first_,
                other.data_.last_,
                data_.first_
            );
        }
        else if (data_.ref_to_alloc() == other.data_.ref_to_alloc())
        {
            data_.first_ = other.data_.first_;
            data_.last_  = other.data_.last_;
            data_.eos_   = other.data_.eos_;

            other.data_.first_ = nullptr;
            other.data_.last_  = nullptr;
            other.data_.eos_   = nullptr;
        }
        else
        {
            const size_type n = other.size();

            check_size(n, "sfl::small_vector::initialize_move");

            if (n > N)
            {
                data_.first_ = sfl::dtl::allocate(data_.ref_to_alloc(), n);
                data_.last_  = data_.first_;
                data_.eos_   = data_.first_ + n;
            }

            SFL_TRY
            {
                data_.last_ = sfl::dtl::uninitialized_move_a
                (
                    data_.ref_to_alloc(),
                    other.data_.first_,
                    other.data_.last_,
                    data_.first_
                );
            }
            SFL_CATCH (...)
            {
                if (n > N)
                {
                    sfl::dtl::deallocate(data_.ref_to_alloc(), data_.first_, n);
                }

                SFL_RETHROW;
            }
        }
    }

    void assign_fill_n(size_type n, const T& value)
    {
        check_size(n, "sfl::small_vector::assign_fill_n");

        if (n <= capacity())
        {
            const size_type size = this->size();

            const pointer new_last = data_.first_ + n;

            if (n <= size)
            {
                sfl::dtl::fill
                (
                    data_.first_,
                    new_last,
                    value
                );

                sfl::dtl::destroy_a
                (
                    data_.ref_to_alloc(),
                    new_last,
                    data_.last_
                );
            }
            else
            {
                sfl::dtl::fill
                (
                    data_.first_,
                    data_.last_,
                    value
                );

                sfl::dtl::uninitialized_fill_a
                (
                    data_.ref_to_alloc(),
                    data_.last_,
                    new_last,
                    value
                );
            }

            data_.last_ = new_last;
        }
        else
        {
            reset(n);

            data_.last_ = sfl::dtl::uninitialized_fill_n_a
            (
                data_.ref_to_alloc(),
                data_.first_,
                n,
                value
            );
        }
    }

    template <typename InputIt>
    void assign_range(InputIt first, InputIt last)
    {
        assign_range(first, last, typename std::iterator_traits<InputIt>::iterator_category());
    }

    template <typename InputIt, typename Sentinel>
    void assign_range(InputIt first, Sentinel last, std::input_iterator_tag)
    {
        pointer curr = data_.first_;

        while (first != last && curr != data_.last_)
        {
            *curr = *first;
            ++curr;
            ++first;
        }

        if (first != last)
        {
            do
            {
                emplace_back(*first);
                ++first;
            }
            while (first != last);
        }
        else if (curr < data_.last_)
        {
            sfl::dtl::destroy_a(data_.ref_to_alloc(), curr, data_.last_);
            data_.last_ = curr;
        }
    }

    template <typename ForwardIt, typename Sentinel>
    void assign_range(ForwardIt first, Sentinel last, std::forward_iterator_tag)
    {
        const size_type n = std::distance(first, last);

        check_size(n, "sfl::small_vector::assign_range");

        if (n <= capacity())
        {
            const size_type size = this->size();

            if (n <= size)
            {
                const pointer new_last = sfl::dtl::copy
                (
                    first,
                    last,
                    data_.first_
                );

                sfl::dtl::destroy_a
                (
                    data_.ref_to_alloc(),
                    new_last,
                    data_.last_
                );

                data_.last_ = new_last;
            }
            else
            {
                const ForwardIt mid = std::next(first, size);

                sfl::dtl::copy
                (
                    first,
                    mid,
                    data_.first_
                );

                data_.last_ = sfl::dtl::uninitialized_copy_a
                (
                    data_.ref_to_alloc(),
                    mid,
                    last,
                    data_.last_
                );
            }
        }
        else
        {
            reset(n);

            data_.last_ = sfl::dtl::uninitialized_copy_a
            (
                data_.ref_to_alloc(),
                first,
                last,
                data_.first_
            );
        }
    }

    void assign_copy(const small_vector& other)
    {
        if (this != &other)
        {
            if (allocator_traits::propagate_on_container_copy_assignment::value)
            {
                if (data_.ref_to_alloc() != other.data_.ref_to_alloc())
                {
                    reset();
                }

                data_.ref_to_alloc() = other.data_.ref_to_alloc();
            }

            assign_range
            (
                other.data_.first_,
                other.data_.last_
            );
        }
    }

    void assign_move(small_vector& other)
    {
        if (allocator_traits::propagate_on_container_move_assignment::value)
        {
            if (data_.ref_to_alloc() != other.data_.ref_to_alloc())
            {
                reset();
            }

            data_.ref_to_alloc() = std::move(other.data_.ref_to_alloc());
        }

        if (other.data_.first_ == other.data_.internal_storage())
        {
            assign_range
            (
                std::make_move_iterator(other.data_.first_),
                std::make_move_iterator(other.data_.last_)
            );
        }
        else if (data_.ref_to_alloc() == other.data_.ref_to_alloc())
        {
            reset();

            data_.first_ = other.data_.first_;
            data_.last_  = other.data_.last_;
            data_.eos_   = other.data_.eos_;

            other.data_.first_ = nullptr;
            other.data_.last_  = nullptr;
            other.data_.eos_   = nullptr;
        }
        else
        {
            assign_range
            (
                std::make_move_iterator(other.data_.first_),
                std::make_move_iterator(other.data_.last_)
            );
        }
    }

    iterator insert_fill_n(const_iterator pos, size_type n, const T& value)
    {
        if (n == 0)
        {
            return begin() + std::distance(cbegin(), pos);
        }

        if (available() >= n)
        {
            const value_type tmp(value);

            const pointer p1 = data_.first_ + std::distance(cbegin(), pos);
            const pointer p2 = p1 + n;

            if (p2 <= data_.last_)
            {
                const pointer p3 = data_.last_ - n;

                const pointer old_last = data_.last_;

                data_.last_ = sfl::dtl::uninitialized_move_a
                (
                    data_.ref_to_alloc(),
                    p3,
                    data_.last_,
                    data_.last_
                );

                sfl::dtl::move_backward
                (
                    p1,
                    p3,
                    old_last
                );

                sfl::dtl::fill
                (
                    p1,
                    p2,
                    tmp
                );
            }
            else
            {
                const pointer old_last = data_.last_;

                sfl::dtl::uninitialized_fill_a
                (
                    data_.ref_to_alloc(),
                    data_.last_,
                    p2,
                    tmp
                );

                data_.last_ = p2;

                data_.last_ = sfl::dtl::uninitialized_move_a
                (
                    data_.ref_to_alloc(),
                    p1,
                    old_last,
                    data_.last_
                );

                sfl::dtl::fill
                (
                    p1,
                    old_last,
                    tmp
                );
            }

            return iterator(p1);
        }
        else
        {
            const difference_type offset = std::distance(cbegin(), pos);

            const size_type new_cap =
                calculate_new_capacity(n, "sfl::small_vector::insert_fill_n");

            pointer new_first;
            pointer new_last;
            pointer new_eos;

            if (new_cap <= N && data_.first_ != data_.internal_storage())
            {
                new_first = data_.internal_storage();
                new_last  = new_first;
                new_eos   = new_first + N;
            }
            else
            {
                new_first = sfl::dtl::allocate(data_.ref_to_alloc(), new_cap);
                new_last  = new_first;
                new_eos   = new_first + new_cap;
            }

            const pointer p = new_first + offset;

            SFL_TRY
            {
                // `value` can be a reference to an element in this
                // container. First we will create `n` copies of `value`
                // and ffter that we can move elements.

                sfl::dtl::uninitialized_fill_n_a
                (
                    data_.ref_to_alloc(),
                    p,
                    n,
                    value
                );

                new_last = nullptr;

                const pointer mid = data_.first_ + offset;

                new_last = sfl::dtl::uninitialized_move_if_noexcept_a
                (
                    data_.ref_to_alloc(),
                    data_.first_,
                    mid,
                    new_first
                );

                new_last += n;

                new_last = sfl::dtl::uninitialized_move_if_noexcept_a
                (
                    data_.ref_to_alloc(),
                    mid,
                    data_.last_,
                    new_last
                );
            }
            SFL_CATCH (...)
            {
                if (new_last == nullptr)
                {
                    sfl::dtl::destroy_n_a
                    (
                        data_.ref_to_alloc(),
                        p,
                        n
                    );
                }
                else
                {
                    sfl::dtl::destroy_a
                    (
                        data_.ref_to_alloc(),
                        new_first,
                        new_last
                    );
                }

                if (new_first != data_.internal_storage())
                {
                    sfl::dtl::deallocate
                    (
                        data_.ref_to_alloc(),
                        new_first,
                        new_cap
                    );
                }

                SFL_RETHROW;
            }

            sfl::dtl::destroy_a
            (
                data_.ref_to_alloc(),
                data_.first_,
                data_.last_
            );

            if (data_.first_ != data_.internal_storage())
            {
                sfl::dtl::deallocate
                (
                    data_.ref_to_alloc(),
                    data_.first_,
                    std::distance(data_.first_, data_.eos_)
                );
            }

            data_.first_ = new_first;
            data_.last_  = new_last;
            data_.eos_   = new_eos;

            return iterator(p);
        }
    }

    template <typename InputIt>
    iterator insert_range(const_iterator pos, InputIt first, InputIt last)
    {
        return insert_range(pos, first, last, typename std::iterator_traits<InputIt>::iterator_category());
    }

    template <typename InputIt, typename Sentinel>
    iterator insert_range(const_iterator pos, InputIt first, Sentinel last, std::input_iterator_tag)
    {
        const difference_type offset = std::distance(cbegin(), pos);

        while (first != last)
        {
            pos = insert(pos, *first);
            ++pos;
            ++first;
        }

        return begin() + offset;
    }

    template <typename ForwardIt, typename Sentinel>
    iterator insert_range(const_iterator pos, ForwardIt first, Sentinel last, std::forward_iterator_tag)
    {
        if (first == last)
        {
            return begin() + std::distance(cbegin(), pos);
        }

        const size_type n = std::distance(first, last);

        if (available() >= n)
        {
            const pointer p1 = data_.first_ + std::distance(cbegin(), pos);
            const pointer p2 = p1 + n;

            if (p2 <= data_.last_)
            {
                const pointer p3 = data_.last_ - n;

                const pointer old_last = data_.last_;

                data_.last_ = sfl::dtl::uninitialized_move_a
                (
                    data_.ref_to_alloc(),
                    p3,
                    data_.last_,
                    data_.last_
                );

                sfl::dtl::move_backward
                (
                    p1,
                    p3,
                    old_last
                );

                sfl::dtl::copy
                (
                    first,
                    last,
                    p1
                );
            }
            else
            {
                const pointer old_last = data_.last_;

                const ForwardIt mid = std::next(first, std::distance(pos, cend()));

                data_.last_ = sfl::dtl::uninitialized_copy_a
                (
                    data_.ref_to_alloc(),
                    mid,
                    last,
                    data_.last_
                );

                data_.last_ = sfl::dtl::uninitialized_move_a
                (
                    data_.ref_to_alloc(),
                    p1,
                    old_last,
                    data_.last_
                );

                sfl::dtl::copy
                (
                    first,
                    mid,
                    p1
                );
            }

            return iterator(p1);
        }
        else
        {
            const difference_type offset = std::distance(cbegin(), pos);

            const size_type new_cap =
                calculate_new_capacity(n, "sfl::small_vector::insert_range");

            pointer new_first;
            pointer new_last;
            pointer new_eos;

            if (new_cap <= N && data_.first_ != data_.internal_storage())
            {
                new_first = data_.internal_storage();
                new_last  = new_first;
                new_eos   = new_first + N;
            }
            else
            {
                new_first = sfl::dtl::allocate(data_.ref_to_alloc(), new_cap);
                new_last  = new_first;
                new_eos   = new_first + new_cap;
            }

            const pointer p = new_first + offset;

            SFL_TRY
            {
                const pointer mid = data_.first_ + offset;

                new_last = sfl::dtl::uninitialized_move_if_noexcept_a
                (
                    data_.ref_to_alloc(),
                    data_.first_,
                    mid,
                    new_first
                );

                new_last = sfl::dtl::uninitialized_copy_a
                (
                    data_.ref_to_alloc(),
                    first,
                    last,
                    new_last
                );

                new_last = sfl::dtl::uninitialized_move_if_noexcept_a
                (
                    data_.ref_to_alloc(),
                    mid,
                    data_.last_,
                    new_last
                );
            }
            SFL_CATCH (...)
            {
                sfl::dtl::destroy_a
                (
                    data_.ref_to_alloc(),
                    new_first,
                    new_last
                );

                if (new_first != data_.internal_storage())
                {
                    sfl::dtl::deallocate
                    (
                        data_.ref_to_alloc(),
                        new_first,
                        new_cap
                    );
                }

                SFL_RETHROW;
            }

            sfl::dtl::destroy_a
            (
                data_.ref_to_alloc(),
                data_.first_,
                data_.last_
            );

            if (data_.first_ != data_.internal_storage())
            {
                sfl::dtl::deallocate
                (
                    data_.ref_to_alloc(),
                    data_.first_,
                    std::distance(data_.first_, data_.eos_)
                );
            }

            data_.first_ = new_first;
            data_.last_  = new_last;
            data_.eos_   = new_eos;

            return iterator(p);
        }
    }
};

//
// ---- NON-MEMBER FUNCTIONS --------------------------------------------------
//

template <typename T, std::size_t N, typename A>
SFL_NODISCARD
bool operator==
(
    const small_vector<T, N, A>& x,
    const small_vector<T, N, A>& y
)
{
    return x.size() == y.size() && std::equal(x.begin(), x.end(), y.begin());
}

template <typename T, std::size_t N, typename A>
SFL_NODISCARD
bool operator!=
(
    const small_vector<T, N, A>& x,
    const small_vector<T, N, A>& y
)
{
    return !(x == y);
}

template <typename T, std::size_t N, typename A>
SFL_NODISCARD
bool operator<
(
    const small_vector<T, N, A>& x,
    const small_vector<T, N, A>& y
)
{
    return std::lexicographical_compare(x.begin(), x.end(), y.begin(), y.end());
}

template <typename T, std::size_t N, typename A>
SFL_NODISCARD
bool operator>
(
    const small_vector<T, N, A>& x,
    const small_vector<T, N, A>& y
)
{
    return y < x;
}

template <typename T, std::size_t N, typename A>
SFL_NODISCARD
bool operator<=
(
    const small_vector<T, N, A>& x,
    const small_vector<T, N, A>& y
)
{
    return !(y < x);
}

template <typename T, std::size_t N, typename A>
SFL_NODISCARD
bool operator>=
(
    const small_vector<T, N, A>& x,
    const small_vector<T, N, A>& y
)
{
    return !(x < y);
}

template <typename T, std::size_t N, typename A>
void swap
(
    small_vector<T, N, A>& x,
    small_vector<T, N, A>& y
)
{
    x.swap(y);
}

template <typename T, std::size_t N, typename A, typename U>
typename small_vector<T, N, A>::size_type
    erase(small_vector<T, N, A>& c, const U& value)
{
    auto it = std::remove(c.begin(), c.end(), value);
    auto r = std::distance(it, c.end());
    c.erase(it, c.end());
    return r;
}

template <typename T, std::size_t N, typename A, typename Predicate>
typename small_vector<T, N, A>::size_type
    erase_if(small_vector<T, N, A>& c, Predicate pred)
{
    auto it = std::remove_if(c.begin(), c.end(), pred);
    auto r = std::distance(it, c.end());
    c.erase(it, c.end());
    return r;
}

} // namespace sfl

#endif // SFL_SMALL_VECTOR_HPP_INCLUDED
