#include <stdio.h>
#include <stdlib.h>
#include <assert.h>

typedef struct node {
    int element;
    struct node* prev;
    struct node* next;
} *Nodeptr, Node;

typedef struct list {
    Nodeptr head, tail, current_node;
} *List;

List dll_create();
void dll_insertafter(List l, int element);
int dll_find_next(List l);
int dll_find_prev(List l);
void dll_insertbefore(List l, int element);
int dll_find(List l, int element);
void dll_find_first(List l);
void dll_find_last(List l);
int dll_retrieve(List l);
void dll_update(List l, int element);
void dll_clear(List l);

List dll_create() {
    List l = malloc(sizeof(struct list));
    l->head = NULL;
    l->tail = NULL;
    l->current_node = NULL;
    return l;
}

void dll_insertafter(List l, int element) {
    Nodeptr n = malloc(sizeof(Node));
    n->element = element;
    n->next = NULL;
    n->prev = NULL;
    if(l->head == NULL) {
        l->head = l->tail = n;
    } else {
        n->next = l->current_node->next;
        if(l->current_node == l->tail) {
            l->tail = n;
        } else {
            l->current_node->next->prev = n;
        }
        l->current_node->next = n;
        n->prev = l->current_node;
    }
    l->current_node = n;
}

int dll_find_next(List l) {
    if(l->current_node == l->tail) return 0;
    l->current_node = l->current_node->next;
    return 1;
}

int dll_find_prev(List l) {
    if(l->current_node == l->head) return 0;
    l->current_node = l->current_node->prev;
    return 1;
}

void dll_insertbefore(List l, int element) {
    if(l->head == NULL) {
        dll_insertafter(l,element);
    } else if(!dll_find_prev(l)) {
        Nodeptr n = malloc(sizeof(Node));
        n->element = element;
        n->next = l->head;
        n->prev = NULL;
        l->head->prev = n;
        l->head = n;
        l->current_node = n;
    } else {
        dll_insertafter(l,element);
    }
}

int dll_find(List l, int element) {
    dll_find_first(l);
    do {
        if(dll_retrieve(l) == element) return 1;
    } while(dll_find_next(l));
    return 0;
}

void dll_find_first(List l) {
    assert(l->head != NULL);
    l->current_node = l->head;
}

void dll_find_last(List l) {
    assert(l->tail != NULL);
    l->current_node = l->tail;
}

int dll_retrieve(List l) {
    assert(l->current_node != NULL);
    return l->current_node->element;
}

void dll_update(List l, int element) {
    assert(l->current_node != NULL);
    l->current_node->element = element;
}

void dll_clear(List l) {
    Nodeptr tmp, iter;
    iter = l->head;
    while(iter != NULL) {
        tmp = iter;
        iter = iter->next;
        free(tmp);
    }

    l->head = NULL;
    l->tail = NULL;
    l->current_node = NULL;
}

int main( int argc, char *argv[] ) {
	List l = dll_create();
    for(int i = 0; i < 10; i++) {
        dll_insertafter(l,i);
    }

    dll_find(l,5);

    do {
        printf("%d\n", dll_retrieve(l));
    } while(dll_find_next(l));

    dll_find_first(l);
    do {
        printf("%d\n", dll_retrieve(l));
    } while(dll_find_next(l));

    dll_clear(l);
	return 0;
}