/* linkedlist.c */
#include <stdlib.h>
#include "linkedlist.h"

//static link head = NULL;
static List ListHead;

link make_node(unsigned char item)
{
    link p = malloc(sizeof *p);
    p->item = item;
    p->next = NULL;
    return p;
}
void free_node(link p)
{
    free(p);
}
link search(unsigned char key)
{
    link p;
    //for (p = head; p; p = p->next)
    for (p = ListHead.head; p; p = p->next)
        if (p->item == key)
            return p;
    return NULL;
}

void insert(link p)
{
    //p->next = head;
    p->next = ListHead.head;
    ListHead.head = p;
}

link delete(link p)
{
    link prev;
    if (p == ListHead.head) {
        ListHead.head = p->next;
        return p;
    }
    for (prev = ListHead.head; prev; prev = prev->next)
        if (prev->next == p) {
            prev->next = p->next;
            return p;
        }
    return NULL;
}

link deleteUniformed(link p)
{
    link prev;
    if (p == ListHead.head) {
        ListHead.head = p->next;
        return p;
    }
    for (prev = ListHead.head; prev; prev = prev->next)
        if (prev->next == p) {
            prev->next = p->next;
            return p;
        }
    return NULL;
}

void traverse(void (*visit)(link))
{
    link p;
    for (p = ListHead.head; p; p = p->next)
        visit(p);
}
void destroy(void)
{
    link q, p = ListHead.head;
    ListHead.head = NULL;
    while (p) {
        q = p;
        p = p->next;
        free(q);
    }
}
void push(link p)
{
    insert(p);
}

link pop(void)
{
    if (ListHead.head == NULL)
        return NULL;
    else
        return delete(ListHead.head);
}