#ifndef LIST_H
#define LIST_H

template<typename T>
class List {
    T *head;
    unsigned int num;
public:
    explicit List();
    [[nodiscard]] T *get_head();
    void set_head(T *head);
    void insert_head(T *elem);
    void insert_tail(T *elem);
    void insert_before(T *elem, T *reference_point);
    void remove(T *elem);
    bool is_empty();
    [[nodiscard]] unsigned int get_num() const;
};

template<typename T>
List<T>::List() : head{nullptr}, num{0} {
}

template<typename T>
T *List<T>::get_head() {
    return head;
}

template<typename T>
void List<T>::set_head(T *head) {
    this->head = head;
}


template<typename T>
void List<T>::insert_head(T *elem) {
    if (!head)
        elem->next = elem->prev = elem;

    else {
        elem->next = head;
        elem->prev = head->prev;
        head->prev->next = elem;
        head->prev = elem;
    }

    this->head = elem;
    ++num;
}

template<typename T>
void List<T>::insert_tail(T *elem) {
    if (!head) {
        elem->next = elem->prev = elem;
        head = elem;
    }
    else {
        elem->next = head;
        elem->prev = head->prev;
        head->prev->next = elem;
        head->prev = elem;
    }
    ++num;
}

template<typename T>
void List<T>::insert_before(T *elem, T *reference_point) {
    elem->next = reference_point;
    elem->prev = reference_point->prev;
    reference_point->prev = elem;
    if (elem->prev == nullptr)
        this->head = elem;
    else
        elem->prev->next = elem;
    ++num;
}

template<typename T>
void List<T>::remove(T *elem) {
    if (elem->next)
        elem->next->prev = elem->prev;
    if (elem->prev)
        elem->prev->next = elem->next;
    if (this->head == elem)
        this->head = elem->next;
    --num;
}

template<typename T>
bool List<T>::is_empty() {
    return this->num == 0;
}

template<typename T>
unsigned int List<T>::get_num() const {
    return num;
}

#endif //LIST_H