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

//TODO: grundlegende Stackfunktionen implementieren:
/*  * `push`: legt ein Element oben auf den Stack,
    * `pop`: entfernt das oberste Element,
    * `top`: liefert das oberste Element zurück,
    * `clearStack`: gibt den gesamten Speicher frei. */

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

// Pushes data as pointer onto the stack.
StackNode *push(StackNode *stack, void *data)
{
  StackNode *node = (StackNode *)malloc(sizeof(StackNode));
  if (node == NULL)
    return stack;  // kein Speicher -> Stack unverändert zurück

  node->data = data;
  node->next = stack;
  return node;
}

// 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;

  StackNode *next = stack->next;
  free(stack);
  return next;
}

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

  return stack->data;
}

// Clears stack and releases all memory.
void clearStack(StackNode *stack)
{
  while (stack != NULL)
  {
    StackNode *next = stack->next;
    free(stack);
    stack = next;
  }
}