#pragma once

#if !defined(BAD_APPLE_OS_STRING_VIEW_INCLUDED)
#define BAD_APPLE_OS_STRING_VIEW_INCLUDED

#include <limits>
#include <stdexcept>
#include <string>

namespace std
{
template<typename CharT, typename Traits = char_traits<CharT>>
class basic_string_view
{
public:
    using traits_type = Traits;
    using value_type = CharT;
    using pointer = CharT*;
    using const_pointer = const CharT*;
    using reference = CharT&;
    using const_reference = const CharT&;
    using iterator = const CharT*;
    using const_iterator = const CharT*;
    // TODO: reverse iterators
    using size_type = size_t;
    using difference_type = ptrdiff_t;
private:
    const_pointer _begin = nullptr;
    const_pointer _end = nullptr;
public:
    constexpr basic_string_view() noexcept = default;
    constexpr basic_string_view(const basic_string_view&) noexcept = default;
    constexpr basic_string_view(const_pointer s, size_type count) noexcept : _begin(s), _end(s + count) {}
    constexpr basic_string_view(const_pointer s) noexcept : _begin(s), _end(s)
    {
        while (*_end) { ++_end; }
    }
    template<typename It, typename End>
    constexpr basic_string_view(It first, End last) noexcept : _begin(first), _end(last) {}
    constexpr basic_string_view(nullptr_t) = delete;

    constexpr basic_string_view& operator=(const basic_string_view&) noexcept = default;

    [[nodiscard]] constexpr iterator begin() const noexcept { return _begin; }
    [[nodiscard]] constexpr const_iterator cbegin() const noexcept { return _begin; }
    [[nodiscard]] constexpr iterator end() const noexcept { return _end; }
    [[nodiscard]] constexpr const_iterator cend() const noexcept { return _end; }
    // TODO: reverse iterators

    [[nodiscard]] constexpr const_reference operator[](size_type pos) const noexcept { return _begin[pos]; }
    [[nodiscard]] constexpr const_reference at(size_type pos) const
    {
        if (pos >= size()) {
            __ba_throw out_of_range();
        }
        return _begin[pos];
    }
    [[nodiscard]] constexpr const_reference front() const noexcept { return *_begin; }
    [[nodiscard]] constexpr const_reference back() const noexcept { return _end[-1]; }
    [[nodiscard]] constexpr const_pointer data() const noexcept { return _begin; }

    [[nodiscard]] constexpr size_type size() const noexcept { return _end - _begin; }
    [[nodiscard]] constexpr size_type length() const noexcept { return _end - _begin; }
    [[nodiscard]] constexpr size_type max_size() const noexcept { return numeric_limits<size_type>::max(); }
    [[nodiscard]] constexpr bool empty() const noexcept { return size() == 0; }

    constexpr void remove_prefix(size_type n) noexcept { _begin += n; }
    constexpr void remove_suffix(size_type n) noexcept { _end -= n; }

    constexpr void swap(basic_string_view& v) noexcept
    {
        swap(_begin, v._begin);
        swap(_end, v._end);
    }
};

using string_view = basic_string_view<char>;
using wstring_view = basic_string_view<wchar_t>;
}

#endif // !defined(BAD_APPLE_OS_STRING_VIEW_INCLUDED)