#include "stack.h"
#include "calls.h"

#define QUANTITY_ADDRESSES 5

enum address_control { get_address, set_address };
void *heap_base;

void init_stack(stack *st)
{
    *st = 0;
}

static void *address_management(void *address, enum address_control state)
{
    enum { null = 0 };
    static void *available_addresses[QUANTITY_ADDRESSES];
    int i;
    if(state == set_address) {
        for(i = 0; i < QUANTITY_ADDRESSES; ++i) {
            if(!available_addresses[i]) {
                available_addresses[i] = address;
                return null;
            }
        }
        return null;
    }
    for(i = 0; i < QUANTITY_ADDRESSES; ++i) {
        if(available_addresses[i]) {
            address = available_addresses[i];
            available_addresses[i] = 0;
            return address;
        }
    }
    return null;
}


void push_stack(stack *st, long num)
{
    struct item *tmp;
    tmp = address_management(0, get_address);
    if(!tmp)
        tmp = sys_alloc(sizeof(struct item));
    if(!heap_base)
        heap_base = tmp;
    tmp->data = num;
    tmp->next = *st;
    *st = tmp;
}

long pop_stack(stack *st)
{
    long num = (*st)->data;
    address_management(*st, set_address);
    *st = (*st)->next;
    return num;
}

int is_empty_stack(const stack *st)
{
    return *st ? 0 : 1;
}

long top_stack(const stack *st)
{
    return (*st)->data;
}