#include <exec/lists.h>
#include <exec/nodes.h>

void *num_to_node(struct List *lst,ULONG num)
{
    struct Node *nd;

    for(nd = lst->lh_Head;
        nd != NULL && nd->ln_Succ != NULL && num > 0;
        nd = nd->ln_Succ, num--) ;

    if(nd == NULL || nd->ln_Succ == NULL) return NULL;
    else return nd;
}

ULONG node_to_num(struct List *lst,void *nd)
{
    struct Node *pos;
    ULONG num = 0;

    for(pos = lst->lh_Head;
        pos != NULL && pos->ln_Succ != NULL && pos != (struct Node *)nd;
        pos = pos->ln_Succ, num++) ;

    if(pos == NULL || pos->ln_Succ == NULL) return ~0;
    else return num;
}

void *head_node(struct List *lst)
{
    if(lst == NULL || lst->lh_Head == NULL || lst->lh_Head->ln_Succ == NULL)
        return NULL;

    return lst->lh_Head;
}

void *tail_node(struct List *lst)
{
    if(lst == NULL || lst->lh_TailPred == NULL || lst->lh_TailPred->ln_Pred == NULL)
        return NULL;

    return lst->lh_TailPred;
}

void *next_node(void *nd)
{
    if( nd == NULL || ((struct Node *)nd)->ln_Succ == NULL
        || ((struct Node *)nd)->ln_Succ->ln_Succ == NULL ) return NULL;

    return ((struct Node *)nd)->ln_Succ;
}

void *prev_node(void *nd)
{
    if( nd == NULL || ((struct Node *)nd)->ln_Pred == NULL
        || ((struct Node *)nd)->ln_Pred->ln_Pred == NULL ) return NULL;

    return ((struct Node *)nd)->ln_Pred;
}