#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) {
        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) {
        return NULL;
    }

    StackNode *topNode = stack;

    stack = stack->next;

    free(topNode);

    return stack;
}

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

    return stack->data;

}

// Clears stack and releases all memory.
StackNode *clearStack(StackNode *stack)
{
    StackNode *current = stack;
    StackNode *next_node;


    while(current){
        next_node = current->next;
        free(current);
        current = next_node;
    }

    return NULL;
}