#include <stdio.h>
#include <malloc.h>
#include <limits.h>

struct Node {
    struct Node *next;
    struct Node *prev;
    void *dta;
};
typedef struct Node Node;

typedef struct {
    Node *head;
    unsigned length;
} List;

List *newList() {
    List *list = malloc(sizeof(List));
    return list;
}

Node *_newNode(Node *next, Node *prev, void *dta) {
    Node *newnode = malloc(sizeof(Node));
    newnode->next = next;
    newnode->prev = prev;
    newnode->dta = dta;
    return newnode;
}

Node *_traverseToLast(Node *node) {
    if (node->next != NULL) {
        return _traverseToLast(node->next);
    } else {
        return node;
    }
}

Node *_traverseToPos(Node *node, int pos) {
    if (pos > 0) {
        if (node->next != NULL) {
            return _traverseToPos(node->next, pos - 1);
        } else {
            return NULL;
        }
    } else {
        return node;
    }
}

void append(List *list, void *elem) {
    if (list->head == NULL) {
        // create head
        list->head = _newNode(NULL, NULL, elem);
    } else {
        // append element
        Node *last = _traverseToLast(list->head);
        last->next = _newNode(NULL, last, elem);
    }
}

int _length(Node *node) {
    if (node->next == NULL) {
        return 1;
    } else {
        return 1 + _length(node->next);
    }
}

int length(List *list) {
    if (list->head == NULL) {
        return 0;
    }
    return _length(list->head);
}

void insert(List *list, int position) {

}

void delete(List *list, int position) {
    Node *todel = _traverseToPos(list->head, position);

    if (todel->prev == NULL) {
        // we are the header
        list->head = todel->next;
        if (list->head != NULL) {
            list->head->prev = NULL;
        }
    } else if (todel->next == NULL) {
        // we are the last item
        todel->prev->next = NULL;
    } else {
        todel->prev->next = todel->next;
        todel->next->prev = todel->prev;
    }

    free(todel);
}

void deleteAll(List *list) {
    while (list->head != NULL) {
        delete(list, 0);
    }
}

void deleteList(List *list) {
    deleteAll(list);
    free(list);
}

List *merge(List *list1, List *list2) {
    return NULL;
}

void *first(List *list) {
    return list->head->dta;
}

void *last(List *list) {
    return _traverseToLast(list->head)->dta;
}

void print(List *list, char *typeFormatter) {
    Node *curr = list->head;
    while (curr != NULL) {
        printf(typeFormatter, curr->dta);
        printf("\n");

        curr = curr->next;
    }
}

int main() {
    printf("Hello, World!\n");
    List *mylist = newList();

    append(mylist, "test");
    append(mylist, "test2");
    append(mylist, "test3");
    print(mylist, "%s");
    printf("length is: %d\n", length(mylist));

    printf("\n");

    deleteAll(mylist);
    printf("length is: %d\n", length(mylist));
    print(mylist, "%s");

    deleteList(mylist);
    return 0;
}