#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 = malloc(sizeof(StackNode));
    newNode->data = data;
    newNode->next = stack;  // Set the new node's next pointer to the current top of the stack.
    return newNode;  // Return the new node as the top of the 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)
    {
        return NULL;  // Nothing to pop if stack is empty.
    }

    StackNode *tempNode = stack;
    stack = stack->next;  // Move the stack pointer to the next node.
    free(tempNode);  // Free the old top node.

    return stack;
}

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

    return stack->data;  // Return the value of the top node.
}

// Clears stack and releases all memory.
void clearStack(StackNode *stack)
{
    while (stack != NULL)
    {
        stack = pop(stack);  // Pop each element and free memory.
    }
}