#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)
{
    //pointer onto new struct
   StackNode* newNode = malloc(sizeof(StackNode));
   newNode->data = data;
    //*stack := first node of the stack; is now the second to first node
   newNode->nextNode = 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)
{
    //getting the second to first node
    StackNode* tmp = stack->nextNode;

    // data should be freed by the caller
    // free(stack->data);
    // stack->data = NULL;
    free(stack);
    stack = NULL;

    return tmp;
}

// Returns the data of the top element.
void* top(StackNode* stack)
{
    //No stack --> No data-pointer
    if (stack == NULL) return NULL;

    return stack->data;
}

// Clears stack and releases all memory.
void clearStack(StackNode* stack)
{
    if (stack == NULL) return;

    if (stack->nextNode != NULL) clearStack(stack->nextNode);

    // date should be freed by the caller.
    // free(stack->data);
    // stack->data = NULL;

    free(stack);
    // technically not needed (dangling pointer)
    stack = NULL;
}