#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)
{
    // this is the new top node
    StackNode *newTopNode = malloc(sizeof(StackNode));

    if (newTopNode == NULL)
    {
        return NULL;
    }

    newTopNode->data = data;
    newTopNode->next = stack;

    return newTopNode;
}

// 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)
    {
        return NULL;
    }
    StackNode *nextNode = stack->next;
    free(stack);
    return nextNode;
}

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

// Clears stack and releases all memory.
void clearStack(StackNode *stack)
{
    while (pop(stack))
        ;
}