/*
Stack implementation

file: stack.c++
author: Jakob Klepp
date: 2017-03-09
*/

#include <cstdlib>
#include "stack.h++"

struct t_layer {
  int value;
  struct t_layer* below;
};

Stack Stack_new() {
  Stack stack = 0;
  return stack;
}

void Stack_destroy(Stack* stack) {
  while (!Stack_isEmpty(stack)) {
    Stack_pop(stack);
  }
}

int Stack_peek(Stack* stack) {
  return (*stack)->value;
}

bool Stack_isEmpty(Stack* stack) {
  return 0 == (*stack);
}

int Stack_pop(Stack* stack) {
  int value = (*stack)->value;
  struct t_layer* below = (*stack)->below;
  delete *stack;
  (*stack) = below;
  return value;
}

void Stack_push(Stack* stack, int value) {
  struct t_layer* newTop = new struct t_layer;
  newTop->below = *stack;
  newTop->value = value;
  *stack = newTop;
}