#include <cassert>
#include <iostream>
#include <sstream>

struct Node
{
    int value { };
    Node* next { };
};

class Circular_List
{
public:

    ~Circular_List()
    {
        while (tail != nullptr)
        {
            pop_front();
        }
    }

    void push_front(int value)
    {
        Node* head { new Node { value } };
        if (tail == nullptr)
        {
            head->next = head;
            tail = head;
        }
        else
        {
            head->next = tail->next;
            tail->next = head;
        }
    }

    int pop_front()
    {
        Node* head { tail->next };
        int value { head->value };

        if (head == tail)
        {
            tail = nullptr;
        }
        else
        {
            tail->next = head->next;
        }

        delete head;
        return value;
    }

    int front() const
    {
        return tail->next->value;
    }

    void rotate()
    {
        if (tail != nullptr)
        {
            tail = tail->next;
        }
    }

    void print(std::ostream& os) const
    {
        os << "[ ";
        if (tail != nullptr)
        {
            Node* head { tail->next };
            do
            {
                os << head->value << " ";
                head = head->next;
            }
            while (head != tail->next);
        }
        os << "]";
    }

private:

    Node* tail { nullptr };

};

void test_const(Circular_List const& list)
{
    assert( list.front() == 10 );
    
    std::ostringstream oss { };
    list.print(oss);
    assert( oss.str() == "[ 10 20 30 ]" );
}

int main()
{
    Circular_List list { };

    {
        std::ostringstream oss { };
        list.print(oss);
        assert( oss.str() == "[ ]" );
    }


    list.rotate();
    {
        std::ostringstream oss { };
        list.print(oss);
        assert( oss.str() == "[ ]" );
    }
    

    list.push_front(10);
    list.push_front(20);
    list.push_front(30);

    {
        std::ostringstream oss { };
        list.print(oss);
        assert( oss.str() == "[ 30 20 10 ]" );   
    }

    // test rotate
    {
        list.rotate();

        std::ostringstream oss { };
        list.print(oss);
        assert( oss.str() == "[ 20 10 30 ]" );
    }

    // test rotate together with pop_front() and push_front()
    {
        list.rotate();
        list.pop_front();
        list.rotate();
        list.push_front(10);

        std::ostringstream oss { };
        list.print(oss);
        assert( oss.str() == "[ 10 20 30 ]" );
    }

    // test that print() and front() also works with const lists
    test_const(list);
}