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

#define T Stack_T

typedef struct elem {
    void *val;
	struct elem *next;
} elem_t;

struct T {
    int count;
	elem_t *head;
};

/* Initial stack */
T Stack_init (void) {
    T stack;
	stack = (T) malloc(sizeof(T));
	stack->count = 0;
	stack->head = NULL;
	return stack;
}

/* Check empty stack*/
int Stack_empty(T stack) {
    assert(stack);
	return stack->count == 0;
}

/* Return size of the stack */
int Stack_size(T stack) {
    assert(stack);
	return stack->count;
}

/* Push an element into the stack */
void Stack_push(T stack, void *val) {
    elem_t *t;

	assert(stack);
	t = (elem_t *) malloc(sizeof(elem_t));
	t->val = val;
    t->next = stack->head;
	stack->head = t;
	stack->count++;
}

/* Pop an element out of the stack */
void *Stack_pop(T stack) {
    void *val;
	elem_t *t;

	assert(stack);
	assert(stack->count > 0);
	t = stack->head;
	stack->head = t->next;
    stack->count--;
	val = t->val;
	free(t);
	return val;
}

/* Print all elements in the stack */
void Stack_print(Stack_T stack) {
    assert(stack);

    int i, size = Stack_size(stack);
	elem_t *current_elem = stack->head;
	printf("Stack [Top --- Bottom]: ");
	for(i = 0; i < size; ++i) {
	    printf("%p ", (int *)current_elem->val);
		current_elem = current_elem->next;
	}
	printf("\n");
}