#include <memory>
#include <stdexcept>

namespace List
{

template<class T>
struct Node
{
	T value;
	std::unique_ptr<Node<T>> next;

	Node(T const & _value)
		: value(_value),
		next(nullptr)
	{}
};

template<class T>
class List
{
protected:
	std::unique_ptr<Node<T>> root;
	Node<T> * tailPtr;
	std::size_t size;

public:
	void Append(T const value)
	{
		++size;

		if(tailPtr == nullptr)
		{
			root = std::make_unique<Node<T>>(value);
			tailPtr = root.get();
			return;
		}

		tailPtr->next = std::make_unique<Node<T>>(value);
		tailPtr = tailPtr->next.get();
	}

	void Prepend(T const value)
	{
		++size;

		if(root == nullptr)
		{
			root = std::make_unique<Node<T>>(value);
			tailPtr = root.get();
			return;
		}

		auto newRoot = std::make_unique<Node<T>>(value);
		newRoot->next.swap(root);
		root.swap(newRoot);
	}

	void Insert(T const value, std::size_t const index)
	{
		if(index >= size)
		{
			throw std::out_of_range("Index is greater or equal to size.");
		}

		if(index == 0u)
		{
			Prepend(value);
			return;
		}

		if(index == size - 1u)
		{
			Append(value);
			return;
		}

		++size;

		Node<T> * prevPtr = root.get();
		Node<T> * curPtr = root->next.get();
		std::size_t currentIndex = 1u;
		while(currentIndex < index)
		{
			prevPtr = curPtr;
			curPtr = curPtr->next().get();
		}

		auto newNode = std::make_unique<Node<T>>(value);
		newNode->next.swap(prevPtr->next);
		prevPtr->next.swap(newNode);
	}

	void Delete(std::size_t const index)
	{
		if(index >= size)
		{
			throw std::out_of_range("Index is greater or equal to size.");
		}

		--size;

		if(index == 0u)
		{
			root.swap(root->next);
			return;
		}

		if(index == size - 1u)
		{
			Node<T> * curPtr = root.get();
			std::size_t currentIndex = 0u;
			while(currentIndex < index - 2u)
			{
				curPtr = curPtr->next().get();
			}

			curPtr->next.release();
			return;
		}

		Node<T> * prevPtr = root.get();
		Node<T> * curPtr = root->next.get();
		std::size_t currentIndex = 1u;
		while(currentIndex < index)
		{
			prevPtr = curPtr;
			curPtr = curPtr->next().get();
		}

		prevPtr->next.swap(curPtr->next);
	}

	T & Front()
	{
		if(size == 0u)
		{
			throw std::out_of_range("List is empty.");
		}

		return root->value;
	}

	T & Back()
	{
		if(size == 0u)
		{
			throw std::out_of_range("List is empty.");
		}

		return tailPtr->value;
	}

	T & operator[](std::size_t const index)
	{
		if(index >= size)
		{
			throw std::out_of_range("Index is greater or equal to size.");
		}

		Node<T> * currentNode = root.get();
		std:size_t currentIndex = 0u;
		while(currentIndex < index)
		{
			currentNode = currentNode->next.get();
		}

		return currentNode->value;
	}

	List()
		: root(nullptr),
		tailPtr(nullptr)
	{}
};
}