#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. */

static StackNode *createNewElement()
{
    return malloc(sizeof(StackNode));
}

// Pushes data as pointer onto the stack.
StackNode *push(StackNode *stack, void *data)
{
    StackNode *node = createNewElement();
    if (node != NULL)
    {
        node->data = data;
        node->next = stack;
        return node;
    }
    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)
{
    if (stack != NULL)
    {
        StackNode *currentElement = stack;
        stack = stack->next;
        
        free(currentElement);
    }
    return stack;
}

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

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

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

        free(stack);

        stack = nextElement;
    }
}