#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. */

// Pushes data as pointer onto the stack.
StackNode *push(StackNode *stack, void *data)
{
StackNode *newNode = (StackNode *)malloc(sizeof(StackNode));
if(newNode == NULL)
  return NULL;
newNode->data = data;
newNode->next = stack;
return newNode;
}

// 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)
{
StackNode *current = stack;

while (current != NULL)
  {
  StackNode *next = current->next;
  free(current);
  current = next;
  }
}