#include <stdio.h>
#include <stdlib.h>
#include "sllist.h"

Sllist *new_sllist()
{
  Sllist *l;
  
  l = (Sllist *) malloc(sizeof(Sllist));
  l->head = NULL;
  l->tail = NULL;
  return l;
}

void free_sllist(Sllist *l)
{
  Sllist_Node *current_node, *next_node;
 
  for (current_node = l->head;
       current_node != NULL;
       current_node = next_node) {
    next_node = current_node->next;
    free(current_node);
  }
  free(l);
}

Sllist_Node *sll_prepend(Sllist *l, void *val)
{
  Sllist_Node *tmp;

  tmp = (Sllist_Node *) malloc(sizeof(Sllist_Node));
  tmp->val = val;
  tmp->next = l->head;

  // make the new element be the head of the list
  l->head = tmp;

  // if the list was empty, make the tail point to the new element
  if (l->tail == NULL)
    l->tail = tmp;
  return tmp;
}

Sllist_Node *sll_append(Sllist *l, void *val)
{
  Sllist_Node *tmp;

  tmp = (Sllist_Node *) malloc(sizeof(Sllist_Node));
  tmp->val = val;
  tmp->next = NULL;
  
  // make the previous tail point to this new element and then update 
  // the list's tail to point to the new element
  if (l->tail != NULL) 
    l->tail->next = tmp;
  l->tail = tmp;
  
  // if the list was empty, made the head point to the new element
  if (l->head == NULL)
    l->head = tmp;
  return tmp;
}


Sllist_Node *sll_insert_after(Sllist *l, Sllist_Node *node, void *val)
{
  Sllist_Node *tmp;

  tmp = (Sllist_Node *) malloc(sizeof(Sllist_Node));
  tmp->val = val;
  tmp->next = node->next;
  node->next = tmp;

  /* if node was the previous tail of the list, then the new element becomes
     the new tail of the list */
  if (l->tail == node)
    l->tail = tmp;
  return tmp;
}

Sllist_Node *sll_first(Sllist *l)
{
  return l->head;
}

Sllist_Node *sll_last(Sllist *l)
{
  return l->tail;
}

Sllist_Node *sll_next(Sllist_Node *n)
{
  return n->next;
}

void *sll_val(Sllist_Node *n) 
{
  return n->val;
}

int sll_empty(Sllist *l)
{
  return (l->head == NULL);
}