#include <stdlib.h>
#include "list.h"

typedef struct lnode {
  void *data;
  struct lnode *next;
} ListNode;

void list_initialize(List *l)
{
  l->head = NULL;
  l->tail = NULL;
}


void 
list_append(List *l, void *data)
{
  ListNode *new_node = (ListNode *) malloc(sizeof(ListNode));

  new_node->data = data;
  new_node->next = NULL;

  if (l->head == NULL) 
    l->head = l->tail = new_node;
  else {
    l->tail->next = new_node;
    l->tail = new_node;
  }
}


void 
list_prepend(List *l, void *data)
{
  ListNode *new_node = (ListNode *) malloc(sizeof(ListNode));

  new_node->data = data;
  new_node->next = l->head;

  if (l->head == NULL) 
    l->head = l->tail = new_node;
  else 
    l->head = new_node;
}


int
list_is_empty(List *l)
{
  return (l->head == NULL);
}


void 
list_get_cursor(List *l, ListCursor *c)
{
  *c = l->head;
}


int 
cursor_at_end(ListCursor c)
{
  return (c == NULL);
}


void *
cursor_advance(ListCursor *c)
{
  *c = (*c)->next;
  if (*c)
    return (*c)->data;
  else
    return NULL;
}


void *
cursor_data(ListCursor c)
{
  if (c)
    return c->data;
  else 
    return NULL;
}


void 
list_destroy(List *l)
{
  ListNode *next, *ptr;

  ptr = l->head;
  while (ptr != NULL) {
    next = ptr->next;
    free(ptr);
    ptr = next;
  }

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


void 
list_do(List *l, void (*action)(void *, void *), 
	void *user_data)
{
  ListNode *ptr, *next;

  ptr = l->head; 
  while (ptr != NULL) {
    next = ptr->next;
    action(ptr->data, user_data);
    ptr = next;
  }
}