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

#include "stack.h"

/* Stack implementation is a linked list with a header */
struct node
{
    elem data;
    ptr_to_node next;
};

int is_empty(stack s)
{
    return s->next == NULL;
}

stack create_stack()
{
    stack s;

    s = malloc(sizeof(struct node));
    if(s == NULL)
        printf("error");
    make_empty(s);
    return s;
}

void make_empty(stack s)
{
    if(s == NULL)
        printf("must create a stack first");
    else
        while(!is_empty(s))
            pop(s);
}

void push(elem x, stack s)
{
    ptr_to_node tmp;

    tmp = malloc(sizeof(struct node));
    if(tmp == NULL)
        printf("out of space");
    else {
        tmp->data = x;
        tmp->next = s->next;
        s->next = tmp;
    }
}

void pop(stack s)
{
    if(!is_empty(s)) {
        ptr_to_node tmp = s->next;
        s->next = s->next->next;
        free(tmp);
    } else
        printf("Empty stack");
}

elem top(stack s)
{
//    if(is_empty(s))
//        printf("empty stack");
//    else
//        return s->next->data;
//
//   return -1;
//
/* tune version */
    if(!is_empty(s))
        return s->next->data;

    printf("empty stack");
    return 0;
}

void print_stack(stack s)
{
    printf("--------\n");
    while(!is_empty(s)) {
        printf("   %d\n", s->next->data);
        s = s->next;
    }
    printf("--------\n");
}

void test()
{
    stack s;
    s = create_stack();
    push(1, s);
    push(2, s);
    print_stack(s);

    push(3, s);
    push(4, s);
    push(5, s);
    print_stack(s);
    printf("%d\n",top(s));

    pop(s);
    print_stack(s);

    pop(s);
    pop(s);
    pop(s);
    pop(s);
    pop(s);
    pop(s);

    print_stack(s);
}

int main()
{
    test();
    return 0;
}