#include <stdlib.h>
#include "stack.h"

typedef struct _Stack {
	void** elems;
	int size;
} Stack;

Stack* stack_init() {
	Stack* s = malloc(sizeof(Stack));
	s->size = 0;
	s->elems = NULL;
	return s;
}

void* stack_pop(Stack* stack) {
	if (stack_empty(stack))
		return NULL;
	stack->size -= 1;
	void* elem = stack->elems[stack->size];
	stack->elems[stack->size] = NULL;
	stack->elems = realloc(stack->elems, stack->size * sizeof(void*));

	return elem;
}

void stack_push(Stack* stack, void* elem) {
	if (stack == NULL)
		return;

	stack->size += 1;
	stack->elems = realloc(stack->elems, stack->size * sizeof(void*));
	stack->elems[stack->size - 1] = elem;
}

void* stack_peek(Stack* stack) {
	if (stack_empty(stack))
		return NULL;
	return stack->elems[stack->size - 1];
}

bool stack_empty(Stack* stack) {
	return (stack == NULL || stack->size == 0);
}

void** stack_clear(Stack** stack) {
	if (*stack == NULL)
		return NULL;
	void** elems = (*stack)->elems;
	free(*stack);
	*stack = NULL;
	return elems;
}