#include <stdlib.h>
#include <stdbool.h>
#include <stdio.h>
#include <assert.h>
#include "stack.h"

static bool invrep(stack s){
    return s != NULL;
}

struct _s_stack{
    stack_elem elem;
    stack next;
};

stack stack_empty(){
    stack empty_stack = NULL;
    return empty_stack;
}

stack stack_push(stack s, stack_elem e){
    stack new_node = malloc(sizeof(stack));
    new_node->elem = e;
    new_node->next = s;

    assert(invrep(new_node));
    return new_node;
}

stack stack_pop(stack s){
    assert(invrep(s));

    stack s_without_head = s->next;
    free(s);

    return s_without_head;
}

unsigned int stack_size(stack s){
    unsigned int s_size = 0;
    while (s != NULL){
        s = s->next;
        s_size++;
    }
    return s_size;
}

stack_elem stack_top(stack s){
    assert(invrep(s));
    return s->elem;
}

bool stack_is_empty(stack s){
    return (s == NULL);
}


stack_elem *stack_to_array(stack s){
    printf("a");
    if (stack_is_empty(s)){
        return NULL;
    }
    printf("b");

    assert(invrep(s));

    stack aux = s;
    unsigned int len = stack_size(s);
    stack_elem *a = calloc(len, sizeof(stack_elem));
    unsigned int i = len;

    for(unsigned int i = len - 1u; i <= 0u ; i--){
        a[i] = aux->elem;
        aux = aux->next;
    }

    assert(invrep(s));
    return a;
}


stack destroy(stack s){
    assert(invrep(s));
    stack d;
    while (s->next != NULL){
        d = s->next;
        free(s);
    }
    free(d);
    return NULL;
}