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#pragma once
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <iterator>
template <typename T>
class RingBuffer {
public:
class Sentinel {};
class Iterator {
public:
friend class RingBuffer;
using difference_type = ptrdiff_t;
using value_type = T;
using pointer = T*;
using reference = T&;
using iterator_category = std::random_access_iterator_tag;
private:
RingBuffer* mContainer;
size_t mCurr;
bool mNeedsWrapAround;
bool mHasWrapped = false;
public:
// NOTE: default constructed Iterator is in an undefined state
T& operator*() const {
return mContainer->mRing[mCurr];
}
Iterator& operator++() {
assert(*this != Sentinel{});
++mCurr;
if (mNeedsWrapAround && mCurr == mContainer->mCapacity) {
mHasWrapped = true;
mCurr = 0;
}
return *this;
}
bool operator==(const Iterator& that) const {
assert(this->mContainer == that.mContainer);
return this->mCurr == that.mCurr;
}
bool operator==(const Sentinel&) const {
return mCurr == mContainer->mTailIdx && (!mNeedsWrapAround || mHasWrapped);
}
};
using value_type = T;
using reference = T&;
using const_reference = const T&;
using iterator = Iterator;
// using const_iterator = void; // TODO
using difference_type = ptrdiff_t;
using size_type = size_t;
private:
T* mRing = nullptr;
size_t mHeadIdx = 0;
size_t mTailIdx = 0;
size_t mCapacity = 0;
size_t mSize = 0;
public:
RingBuffer() noexcept = default;
~RingBuffer() noexcept {
delete mRing;
}
RingBuffer(const RingBuffer&) noexcept = delete;
RingBuffer& operator=(const RingBuffer&) noexcept = delete;
RingBuffer(RingBuffer&& that) noexcept
: mRing{ that.mRing }
, mHeadIdx{ that.mHeadIdx }
, mTailIdx{ that.mTailIdx }
, mCapacity{ that.mCapacity }
, mSize{ that.mSize } {
that.mRing = nullptr;
}
RingBuffer& operator=(RingBuffer&& that) noexcept {
if (this != &that) {
auto oldThisRing = this->mRing;
this->mRing = that.mRing;
that.mRing = nullptr;
delete oldThisRing;
this->mHeadIdx = that.mHeadIdx;
this->mTailIdx = that.mTailIdx;
this->mCapacity = that.mCapacity;
this->mSize = that.mSize;
}
return *this;
}
Iterator begin() {
Iterator it;
it.mContainer = this;
it.mCurr = mHeadIdx;
it.mNeedsWrapAround = mHeadIdx >= mTailIdx;
return it;
}
Sentinel end() {
return Sentinel{};
}
const T& operator[](size_t i) const {
size_t idx = mHeadIdx + i;
if (idx >= mCapacity) {
idx -= mCapacity;
}
return mRing[idx];
}
T& operator[](size_t i) { return const_cast<T&>(const_cast<const RingBuffer&>(*this)[i]); }
void push_back(T t) {
if (mTailIdx == mCapacity) {
// Ring buffer is filled to the right, warp around to the beginning
// mHeadIdx > 0 must be true, since we checked that as condition (1) above
mRing[0] = std::move(t);
mTailIdx = 1;
} else {
mRing[mTailIdx] = std::move(t);
mTailIdx += 1;
}
// Push mHeadIdx backwards if overwrote element in a filled buffer
bool bufferFilled = mSize == mCapacity;
if (bufferFilled && mTailIdx > mHeadIdx) {
mHeadIdx += 1;
if (mHeadIdx == mCapacity) {
mHeadIdx = 0;
}
}
if (!bufferFilled) {
++mSize;
}
}
[[nodiscard]] size_t capacity() const {
return mCapacity;
}
[[nodiscard]] size_t size() const {
return mSize;
}
[[nodiscard]] T* GetBuffer() const { return mRing; }
[[nodiscard]] size_t GetHeadIdx() const { return mHeadIdx; }
[[nodiscard]] size_t GetTailIdx() const { return mTailIdx; }
void resize(size_t newCapacity) {
auto size = this->size();
auto oldRing = mRing;
auto newRing = mRing = new T[newCapacity];
std::rotate_copy(oldRing, oldRing + mHeadIdx, oldRing + mCapacity, newRing);
delete oldRing;
mCapacity = newCapacity;
mHeadIdx = 0;
mTailIdx = size;
}
};
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