SimpleRingBuffer.h

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#pragma once
 
#include <cassert>
#include <concepts>
#include <cstddef>
#include <iterator>
#include <ostream>
 
namespace ArcdpsExtension {
    template<typename T, typename Allocator = std::allocator<T>>
    class RingBuffer {
    public:
        explicit RingBuffer(size_t pInitialCapacity) {
            mCapacityBegin = mAlloc.allocate(pInitialCapacity);
            // mCapacityBegin = static_cast<T*>(calloc(pInitialCapacity, sizeof(T)));
            mCapacityEnd = mCapacityBegin + pInitialCapacity;
            mCurrent = mCapacityBegin;
            mSizeEnd = mCapacityBegin;
        }
 
        virtual ~RingBuffer() {
            if (mCapacityBegin) {
                Clear();
                mAlloc.deallocate(mCapacityBegin, mCapacityEnd - mCapacityBegin);
            }
        }
 
        RingBuffer(const RingBuffer& pOther) {
            size_t size = pOther.Size();
            mCapacityBegin = mAlloc.allocate(size);
            mCapacityEnd = mCapacityBegin + size;
            mCurrent = mCapacityBegin;
            mSizeEnd = mCapacityBegin;
 
            for (const auto& other : pOther) {
                PushBack(other);
            }
        }
 
        RingBuffer(RingBuffer&& pOther) noexcept
            : mCurrent(pOther.mCurrent),
              mSizeEnd(pOther.mSizeEnd),
              mCapacityBegin(pOther.mCapacityBegin),
              mCapacityEnd(pOther.mCapacityEnd),
              mAlloc(std::move(pOther.mAlloc)) {
            pOther.mCapacityBegin = nullptr;
        }
 
        RingBuffer& operator=(const RingBuffer& pOther) {
            if (this == &pOther)
                return *this;
            size_t size = pOther.Size();
            mCapacityBegin = mAlloc.allocate(size);
            mCapacityEnd = mCapacityBegin + size;
            mCurrent = mCapacityBegin;
            mSizeEnd = mCapacityBegin;
 
            for (const auto& other : pOther) {
                PushBack(other);
            }
            return *this;
        }
 
        RingBuffer& operator=(RingBuffer&& pOther) noexcept {
            if (this == &pOther)
                return *this;
            mCurrent = pOther.mCurrent;
            mSizeEnd = pOther.mSizeEnd;
            mCapacityBegin = pOther.mCapacityBegin;
            mCapacityEnd = pOther.mCapacityEnd;
            mAlloc = std::move(pOther.mAlloc);
            pOther.mCapacityBegin = nullptr;
            return *this;
        }
 
        void PushBack(T&& pElement);
        void PushBack(const T& pElement);
 
        template<typename... Args>
        void EmplaceBack(const Args&... args);
 
        T& Back();
        const T& Back() const;
 
        void Clear();
        size_t Size() const;
        void Resize(size_t pNewCapacity);
 
        const T& operator[](size_t pNum) const;
        T& operator[](size_t pNum);
 
        class RingBufferIterator {
        public:
            using difference_type = std::ptrdiff_t;
            using value_type = T;
            using pointer = T*;
            using reference = T&;
            using iterator_category = std::random_access_iterator_tag;
            using iterator_concept = std::random_access_iterator_tag;
 
            RingBufferIterator() = default;
 
            RingBufferIterator(pointer pPtr, bool pBegin, bool pEnd, const RingBuffer<T, Allocator>* pParent)
                : mPtr(pPtr),
                  mBegin(pBegin),
                  mEnd(pEnd),
                  mParent(pParent) {}
 
            // COPY & MOVE
            RingBufferIterator(const RingBufferIterator& pOther) = default;
            RingBufferIterator(RingBufferIterator&& pOther) noexcept = default;
            RingBufferIterator& operator=(const RingBufferIterator& pOther) = default;
            RingBufferIterator& operator=(RingBufferIterator&& pOther) noexcept = default;
 
            // comparators
            bool operator==(const RingBufferIterator&) const = default;
 
            // Relation comparison relys on uintptr_t "underflow". It basically means, that the comparison breaks, when the size is bigger than `size_t / 2`.
            std::strong_ordering operator<=>(const RingBufferIterator& pOther) const {
                uintptr_t thisDiff = (uintptr_t) mPtr - (uintptr_t) (mParent->mCurrent);
                uintptr_t otherDiff = (uintptr_t) pOther.mPtr - (uintptr_t) (mParent->mCurrent);
                if ((mEnd && !pOther.mEnd) || (pOther.mBegin && !mBegin)) {
                    return std::strong_ordering::greater;
                }
                if ((mBegin && pOther.mBegin) || (pOther.mEnd && !mEnd)) {
                    return std::strong_ordering::less;
                }
                return thisDiff <=> otherDiff;
            }
 
            // dereferencable
            reference operator*() const { return *mPtr; }
 
            // helper
            pointer operator->() const { return mPtr; }
 
            // Prefix increment
            RingBufferIterator& operator++() {
                assert(mEnd == false && "Called ++ on an end iterator");
                mBegin = false;
                mPtr = mParent->advance(mPtr);
                if (mParent->mCurrent == mPtr) mEnd = true;
                return *this;
            }
 
            RingBufferIterator& operator--() {
                assert(mBegin == false && "Called -- on an begin iterator");
                mEnd = false;
                mPtr = mParent->retreat(mPtr);
                if (mParent->mCurrent == mPtr) mBegin = true;
                return *this;
            }
 
            // Postfix increment
            RingBufferIterator operator++(int) {
                RingBufferIterator tmp = *this;
                this->operator++();
                return tmp;
            }
 
            RingBufferIterator operator--(int) {
                RingBufferIterator tmp = *this;
                this->operator--();
                return tmp;
            }
 
            // calculation operators
            // with itself
            difference_type operator-(const RingBufferIterator& pOther) const {
                std::ptrdiff_t thisDiff = mPtr - mParent->mCurrent;
                std::ptrdiff_t otherDiff = pOther.mPtr - mParent->mCurrent;
                std::ptrdiff_t fullDiff = mParent->mSizeEnd - mParent->mCapacityBegin;
                if (thisDiff < 0 || (mEnd && thisDiff == 0)) {
                    thisDiff += fullDiff;
                }
                if (otherDiff < 0 || (pOther.mEnd && thisDiff == 0)) {
                    otherDiff += fullDiff;
                }
                return thisDiff - otherDiff;
            }
 
            // with numbers
            RingBufferIterator& operator+=(const difference_type pNum) {
                assert(*this - mParent->begin() + pNum <= mParent->end() - mParent->begin() && "tried to move iterator after end!");
 
                mBegin = false;
                mPtr += pNum;
                if (mPtr >= mParent->mSizeEnd) {
                    mPtr = mPtr - mParent->mSizeEnd + mParent->mCapacityBegin;
                }
                if (mParent->mCurrent == mPtr) mEnd = true;
                return *this;
            }
 
            RingBufferIterator operator+(const difference_type pNum) const {
                RingBufferIterator it = *this;
                it += pNum;
                return it;
            }
 
            friend RingBufferIterator operator+(const difference_type pLhs, const RingBufferIterator& pRhs) {
                RingBufferIterator it = pRhs;
                it += pLhs;
                return it;
            }
 
            RingBufferIterator& operator-=(const difference_type pNum) {
                assert(*this - mParent->begin() - pNum >= 0 && "tried to move iterator before begin!");
 
                mEnd = false;
                mPtr -= pNum;
                if (mPtr < mParent->mCapacityBegin) {
                    mPtr = (T*) ((uintptr_t) mPtr + (uintptr_t) mParent->mSizeEnd - (uintptr_t) mParent->mCapacityBegin);
                }
                if (mParent->mCurrent == mPtr) mBegin = true;
                return *this;
            }
 
            RingBufferIterator operator-(const difference_type pNum) const {
                RingBufferIterator it = *this;
                it -= pNum;
                return it;
            }
 
            // for some reason the const function has to return a non-const reference...
            // The standard says so, so we have to conform it: `{  j[n]  } -> std::same_as<std::iter_reference_t<I>>;` with `const I j`.
            // https://en.cppreference.com/w/cpp/iterator/random_access_iterator
            reference operator[](const difference_type pNum) const {
                return *(mParent->begin() + pNum);
            }
 
            /*
         * Only use for debugging!
         */
            friend std::ostream& operator<<(std::ostream& pOs, const RingBufferIterator& pObj) {
                return pOs
                       << "mPtr: " << pObj.mPtr
                       << " mBegin: " << pObj.mBegin
                       << " mEnd: " << pObj.mEnd
                       << " mParent: " << pObj.mParent;
            }
 
        private:
            pointer mPtr = nullptr;
            bool mBegin = false;
            bool mEnd = false;
            const RingBuffer<T>* mParent = nullptr;
        };
 
 
        static_assert(std::random_access_iterator<RingBufferIterator>);
 
        // pointer pPtr, bool pBegin, bool pEnd, RingBuffer* pParent
        RingBufferIterator begin() { return RingBufferIterator(mCurrent, true, mSizeEnd == mCapacityBegin, this); }
        RingBufferIterator end() { return RingBufferIterator(mCurrent, mSizeEnd == mCapacityBegin, true, this); }
        const RingBufferIterator begin() const { return RingBufferIterator(mCurrent, true, mSizeEnd == mCapacityBegin, this); }
        const RingBufferIterator end() const { return RingBufferIterator(mCurrent, mSizeEnd == mCapacityBegin, true, this); }
        const RingBufferIterator cbegin() const { return RingBufferIterator(mCurrent, true, mSizeEnd == mCapacityBegin, this); }
        const RingBufferIterator cend() const { return RingBufferIterator(mCurrent, mSizeEnd == mCapacityBegin, true, this); }
        RingBufferIterator rbegin() { return std::make_reverse_iterator(end()); }
        RingBufferIterator rend() { return std::make_reverse_iterator(begin()); }
        const RingBufferIterator rbegin() const { return std::make_reverse_iterator(end()); }
        const RingBufferIterator rend() const { return std::make_reverse_iterator(begin()); }
        const RingBufferIterator crbegin() const { return std::make_reverse_iterator(end()); }
        const RingBufferIterator crend() const { return std::make_reverse_iterator(begin()); }
 
    private:
        T* mCurrent;
        T* mSizeEnd;
        T* mCapacityBegin;
        T* mCapacityEnd;
        Allocator mAlloc;
 
        T* pushOne();
        [[nodiscard]] T* advance(T* pElem) const;
        [[nodiscard]] T* retreat(T* pElem) const;
    };
} // namespace ArcdpsExtension
 
// test if the range is also valid
static_assert(std::ranges::random_access_range<ArcdpsExtension::RingBuffer<uint64_t>>);
static_assert(std::ranges::random_access_range<const ArcdpsExtension::RingBuffer<uint64_t>>);
 
template<typename T, typename Allocator>
void ArcdpsExtension::RingBuffer<T, Allocator>::PushBack(T&& pElement) {
    T* elem = pushOne();
    new (elem) T(pElement);
}
 
template<typename T, typename Allocator>
void ArcdpsExtension::RingBuffer<T, Allocator>::PushBack(const T& pElement) {
    T* elem = pushOne();
    new (elem) T(pElement);
}
 
template<typename T, typename Allocator>
T* ArcdpsExtension::RingBuffer<T, Allocator>::pushOne() {
    // If first element
    if (mSizeEnd == mCapacityBegin) {
        ++mSizeEnd;
        return mCapacityBegin;
    }
 
    if (mSizeEnd != mCapacityEnd) {
        T* current = mSizeEnd;
        ++mSizeEnd;
        return current;
    }
 
    // advance begin and end
    T* current = mCurrent;
    mCurrent = advance(mCurrent);
 
    current->~T();
    return current;
}
 
template<typename T, typename Allocator>
T* ArcdpsExtension::RingBuffer<T, Allocator>::advance(T* pElem) const {
    auto val = pElem + 1;
    if (val >= mSizeEnd) return mCapacityBegin;
    return val;
}
 
template<typename T, typename Allocator>
T* ArcdpsExtension::RingBuffer<T, Allocator>::retreat(T* pElem) const {
    auto val = pElem;
    if (val <= mCapacityBegin) val = mSizeEnd;
    --val;
    return val;
}
 
template<typename T, typename Allocator>
template<typename... Args>
void ArcdpsExtension::RingBuffer<T, Allocator>::EmplaceBack(const Args&... args) {
    T* elem = pushOne();
    new (elem) T(args...);
}
 
template<typename T, typename Allocator>
T& ArcdpsExtension::RingBuffer<T, Allocator>::Back() {
    return *retreat(mCurrent);
}
 
template<typename T, typename Allocator>
const T& ArcdpsExtension::RingBuffer<T, Allocator>::Back() const {
    return *retreat(mCurrent);
}
 
template<typename T, typename Allocator>
void ArcdpsExtension::RingBuffer<T, Allocator>::Clear() {
    for (auto it = begin(); it != end(); ++it) {
        (*it).~T();
    }
 
    mCurrent = mSizeEnd = mCapacityBegin;
}
 
template<typename T, typename Allocator>
size_t ArcdpsExtension::RingBuffer<T, Allocator>::Size() const {
    return mSizeEnd - mCapacityBegin;
}
 
template<typename T, typename Allocator>
void ArcdpsExtension::RingBuffer<T, Allocator>::Resize(size_t pNewCapacity) {
    // backup old data
    T* current = mCurrent;
    T* sizeEnd = mSizeEnd;
    T* capacityBegin = mCapacityBegin;
    T* capacityEnd = mCapacityEnd;
 
    // allocate new memory
    mCapacityBegin = mAlloc.allocate(pNewCapacity);
    // mCapacityBegin = static_cast<T*>(calloc(pInitialCapacity, sizeof(T)));
    mCapacityEnd = mCapacityBegin + pNewCapacity;
    mCurrent = mCapacityBegin;
    mSizeEnd = mCapacityBegin;
 
    // iterate over old elements and move them
    // Also deconstruct them
    // if there are old elements
    T* val = current;
    while (sizeEnd != capacityBegin) {
        PushBack(std::move(*val));
        val->~T();
 
        val = val + 1;
        if (val >= sizeEnd) val = capacityBegin;
        if (val == current) break;
    }
 
    // deallocate old ram
    mAlloc.deallocate(capacityBegin, capacityEnd - capacityBegin);
}
 
template<typename T, typename Allocator>
const T& ArcdpsExtension::RingBuffer<T, Allocator>::operator[](size_t pNum) const {
    const auto var = begin() + pNum;
    return *var;
}
 
template<typename T, typename Allocator>
T& ArcdpsExtension::RingBuffer<T, Allocator>::operator[](size_t pNum) {
    auto var = begin() + pNum;
    return *var;
}