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

// Pushes data as pointer onto the stack.
StackNode *push(StackNode *stack, void *data)
{
  if (!data)
  {
    return stack; //Nichts pushen
  }
  
      StackNode *t = (StackNode *)malloc(sizeof(StackNode));
      if(!t)
        {
        return NULL; //Speicherfehler
        }
      t->next = stack;
      t->data = data;
      return t; //Gibt den ersten StackNode des Stacks zurueck
      
    return NULL;
}

// Deletes the top element of the stack (latest added element) and releases its memory. (Pointer to data has to be
// freed by caller.)
StackNode *pop(StackNode *stack)
{
    if(stack == NULL)
      {
        return NULL;
      }
    return stack->next;
}

// Returns the data of the top element.
void *top(StackNode *stack)
{
    if(stack)
      {
      return stack->data;
      }
    return NULL;
}

// Clears stack and releases all memory.
void clearStack(StackNode *stack)
{
  while(stack)
  {
      StackNode *tmp = stack; //merkt sich den momentanen obersten Knoten
      stack = stack->next; //setzt den obersten Knoten auf den Zweiten im Stack
      free(tmp->data);
      free(tmp);
  }
}