#include <vector>
#include <string>
#include <initializer_list>
#include <memory>

class StrBlobPtr;

class StrBlob
{
public:
	friend class StrBlobPtr;
	typedef std::vector<std::string>::size_type size_type;

	StrBlob();
	StrBlob(std::initializer_list<std::string> il);
	size_type size() const { return data->size(); }
	bool empty() const { return data->empty(); }
	void push_back(const std::string &t) { data->push_back(t); }
	void pop_back();
	std::string& front();
	std::string& back();
	std::string& front() const;
	std::string& back()  const;

	StrBlobPtr begin() { return StrBlobPtr(*this); }
	StrBlobPtr end()
	{
		auto ret = StrBlobPtr(*this, data->size());
		return ret;
	}

private:
	std::shared_ptr<std::vector<std::string>> data;
	void check(size_type i, const std::string &msg) const;
};

class StrBlobPtr
{
public:
	typedef std::shared_ptr<std::vector<std::string>> sh_ptr;

	StrBlobPtr() : curr(0) {}
	StrBlobPtr(StrBlob &a, std::size_t sz = 0)
		: wptr(a.data), curr(sz) {}
	std::string& deref() const;
	StrBlobPtr& incr();
private:
	sh_ptr check(std::size_t, const std::string&) const;
	std::weak_ptr<std::vector<std::string>> wptr;
	std::size_t curr;
};

StrBlob::StrBlob()
	: data(std::make_shared<std::vector<std::string>>()) {}

StrBlob::StrBlob(std::initializer_list<std::string> il)
	: data(std::make_shared<std::vector<std::string>>(il)) {}

void StrBlob::check(size_type i, const std::string &msg) const
{
	if (i >= data->size())
		throw std::out_of_range(msg);
}

std::string& StrBlob::front()
{
	check(0, "front on empty StrBlob");
	return data->front();
}

std::string& StrBlob::back()
{
	check(0, "back on empty StrBlob");
	return data->back();
}

std::string& StrBlob::front() const
{
	check(0, "const back on empty StrBlob");
	return data->front();
}

std::string& StrBlob::back() const
{
	check(0, "const back on empty StrBlob");
	return data->back();
}

void StrBlob::pop_back()
{
	check(0, "pop_back on empty StrBlob");
	return data->pop_back();
}



StrBlobPtr::sh_ptr StrBlobPtr::check(std::size_t i, const std::string &msg) const
{
	auto ret = wptr.lock();
	if (!ret)
		throw std::runtime_error("Unbound StrBlobPtr");
	if (i >= ret->size())
		throw std::out_of_range(msg);
	return ret;
}

std::string& StrBlobPtr::deref() const
{
	auto p = check(curr, "dereference past end");
	return (*p)[curr];
}

StrBlobPtr& StrBlobPtr::incr()
{
	auto p = check(curr, "increment past end");
	++curr;
	return *this;
}