#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 *top = malloc(sizeof(StackNode));
    top->next= stack;
    top->data= data;
    return top;
}

// 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;
    }
}