YYCCommonplace/src/yycc/patch/libcxx/enumerate.hpp

#pragma once
#include "../../macro/stl_detector.hpp"

#if defined(YYCC_STL_CLANGSTL)

/**
 * @private
 * @file This is the polyfill for LLVM libcxx std::enumerate.
 * This should be removed once libcxx provide it.
 * This polyfill is generated by AI.
 */

#include <ranges>
#include <utility>
#include <tuple>
#include <cstddef>
#include <iterator>

namespace std::ranges::views {

        // 简化的enumerate实现
        namespace detail {

            template<typename R>
            class enumerate_view {
            private:
                R _range;
                size_t _start;

                template<bool Const>
                class iterator {
                    using Base = conditional_t<Const, const R, R>;
                    using Iter = decltype(std::ranges::begin(std::declval<Base&>()));

                    Iter _iter;
                    size_t _index;

                public:
                    using iterator_category = typename std::iterator_traits<Iter>::iterator_category;
                    using value_type = std::tuple<size_t, decltype(*_iter)>;
                    using difference_type = typename std::iterator_traits<Iter>::difference_type;

                    iterator(Iter iter, size_t index) : _iter(iter), _index(index) {}

                    auto operator*() const { return std::tuple<size_t, decltype(*_iter)>(_index, *_iter); }

                    iterator& operator++() {
                        ++_iter;
                        ++_index;
                        return *this;
                    }

                    iterator operator++(int) {
                        auto tmp = *this;
                        ++*this;
                        return tmp;
                    }

                    bool operator==(const iterator& other) const { return _iter == other._iter; }

                    bool operator!=(const iterator& other) const { return _iter != other._iter; }

                    // 支持双向迭代
                    iterator& operator--()
                        requires std::bidirectional_iterator<Iter>
                    {
                        --_iter;
                        --_index;
                        return *this;
                    }

                    iterator operator--(int)
                        requires std::bidirectional_iterator<Iter>
                    {
                        auto tmp = *this;
                        --*this;
                        return tmp;
                    }
                };

            public:
                enumerate_view(R range, size_t start = 0) : _range(std::move(range)), _start(start) {}

                auto begin() { return iterator<false>(std::ranges::begin(_range), _start); }
                auto end() { return iterator<false>(std::ranges::end(_range), _start + std::ranges::distance(_range)); }

                auto begin() const { return iterator<true>(std::ranges::begin(_range), _start); }
                auto end() const { return iterator<true>(std::ranges::end(_range), _start + std::ranges::distance(_range)); }
            };

            // 适配器函数对象
            struct enumerate_fn {
                template<std::ranges::range R>
                auto operator()(R&& r, size_t start = 0) const {
                    return enumerate_view<std::ranges::views::all_t<R>>(std::forward<R>(r), start);
                }

                // 用于管道操作符的版本
                auto operator()(size_t start = 0) const {
                    return [start](auto&& r) {
                        return enumerate_view<std::ranges::views::all_t<decltype(r)>>(std::forward<decltype(r)>(r), start);
                    };
                }
            };

        } // namespace detail

        inline constexpr detail::enumerate_fn enumerate;

} // namespace std::ranges::views

#endif