#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;
	}
};