FilterMap.h

#pragma once
 
#include "../Common.h"
#include "../util/TraitImpl.h"
 
namespace CXXIter {
 
    // ################################################################################################
    // FILTERMAP
    // ################################################################################################
    namespace op {
        template<typename TChainInput, typename TFilterMapFn, typename TItem>
        class [[nodiscard(CXXITER_CHAINER_NODISCARD_WARNING)]] FilterMap : public IterApi<FilterMap<TChainInput, TFilterMapFn, TItem>> {
            friend struct trait::Iterator<FilterMap<TChainInput, TFilterMapFn, TItem>>;
            friend struct trait::DoubleEndedIterator<FilterMap<TChainInput, TFilterMapFn, TItem>>;
        private:
            TChainInput input;
            TFilterMapFn filterMapFn;
        public:
            constexpr FilterMap(TChainInput&& input, TFilterMapFn filterMapFn) : input(std::move(input)), filterMapFn(filterMapFn) {}
        };
    }
    // ------------------------------------------------------------------------------------------------
    template<typename TChainInput, typename TFilterMapFn, typename TItem>
    struct trait::Iterator<op::FilterMap<TChainInput, TFilterMapFn, TItem>> {
        using ChainInputIterator = trait::Iterator<TChainInput>;
        using InputItem = typename TChainInput::Item;
        // CXXIter Interface
        using Self = op::FilterMap<TChainInput, TFilterMapFn, TItem>;
        using Item = TItem;
 
        static constexpr inline IterValue<Item> next(Self& self) {
            while(true) {
                auto item = ChainInputIterator::next(self.input);
                if(!item.has_value()) [[unlikely]] { return {}; }
                std::optional<Item> value(self.filterMapFn(std::forward<InputItem>( item.value() )));
                if(!value) { continue; }
                return *value;
            }
        }
        static constexpr inline SizeHint sizeHint(const Self& self) {
            SizeHint input = ChainInputIterator::sizeHint(self.input);
            return SizeHint(0, input.upperBound);
        }
        static constexpr inline size_t advanceBy(Self& self, size_t n) { return util::advanceByPull(self, n); }
    };
    template<CXXIterDoubleEndedIterator TChainInput, typename TFilterMapFn, typename TItem>
    struct trait::DoubleEndedIterator<op::FilterMap<TChainInput, TFilterMapFn, TItem>> {
        using ChainInputIterator = trait::DoubleEndedIterator<TChainInput>;
        using InputItem = typename TChainInput::Item;
        // CXXIter Interface
        using Self = op::FilterMap<TChainInput, TFilterMapFn, TItem>;
        using Item = TItem;
 
        static constexpr inline IterValue<Item> nextBack(Self& self) {
            while(true) {
                auto item = ChainInputIterator::nextBack(self.input);
                if(!item.has_value()) [[unlikely]] { return {}; }
                std::optional<Item> value(self.filterMapFn(std::forward<InputItem>( item.value() )));
                if(!value) { continue; }
                return *value;
            }
        }
    };
 
}