#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 *tempNode, *newNode;

    newNode = malloc(sizeof(StackNode));
    newNode->value = 3;
    newNode->next = NULL;

    if (stack == NULL)
    {
        stack = newNode;
        return stack;
    }

    tempNode = stack;
    while (tempNode->next != NULL)
    {
        tempNode = tempNode->next;
    }
    tempNode->next = newNode;

    return stack;
}

// 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)
{
    StackNode *tempNode;

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

    tempNode = stack;
    while (tempNode->next->next != NULL)
    {
        tempNode = tempNode->next;
    }
    free(tempNode->next);
    tempNode->next = NULL;

    return stack;
}

// Returns the data of the top element.
void *top(StackNode *stack)
{
    StackNode *tempNode;

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

    tempNode = stack;
    while (tempNode->next != NULL)
    {
        tempNode = tempNode->next;
    }

    return &tempNode->value;
}

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

    if (stack == NULL)
    {
        return;
    }

    tempNode = stack;
    while (tempNode != NULL)
    {
        tempNode = pop(tempNode);
    }
}